MANIPULATION OF LIGHT ENVIRONMENT TO CONTROL …prr.hec.gov.pk › jspui › bitstream › 123456789 › 838 › 1 › 1888S.pdf · MANIPULATION OF LIGHT ENVIRONMENT TO CONTROL FLOWER

MANIPULATION OF LIGHT ENVIRONMENT TO

CONTROL FLOWER DEVELOPMENT AND

PLANT HEIGHT OF ANNUAL ORNAMENTALS

JALAL-UD-DIN BALOCH

A dissertation submitted in partial fulfillment

of the requirements for the degree of Doctor of Philosophy in Horticulture

DEPARTMENT OF HORTICULTURE FACULTY OF AGRICULTURE

GOMAL UNIVERSITY DERA ISMAIL KHAN

2009

To The Controller of Examinations Gomal University Dera Ismail Khan

Subject: Submission of Ph.D. Dissertation We, the Supervisory Committee, certify that contents and form of dissertation

submitted by Mr. Jalal-ud-Din Baloch have been found satisfactory and

recommend for submission and evaluation.

____________________________________ SUPERVISOR PROF. DR. MUHAMMAD QASIM KHAN FACULTY OF AGRICULTURE GOMAL UNIVERSITY DERA ISMAIL KHAN ____________________________________ CO-SUPERVISOR DR. MUHAMMAD ZUBAIR ASSISTANT PROFESSOR BAHAUDIN ZAKARIA UNIVERSITY MULATN ____________________________________ CHAIRMAN DR. MUHAMMAD SALEEM JILANI DEPARTMENT OF HORTICULTURE FACULTY OF AGRICULTURE GOMAL UNIVERSITY DERA ISMAIL KHAN ____________________________________ DEAN PROF. DR. MUHAMMAD QASIM KHAN BOARD OF STUDIES FACULTY OF AGRICULTURE GOMAL UNIVERSITY DERA ISMAIL KHAN

DEDICATION

To my late father

Sardar Salahuddin Khan Baloch

ACKNOWLEDGEMENTS

The author is highly indebted to the following people for their academic help, guidance, critical analysis and suggestions on thesis, application and validation of models during the course of this study:

Professor Dr. Muhammad Qasim Khan, Dean, Faculty of Agriculture, Gomal

University, Dera Ismail Khan.

Dr. Muhammad Zubair, Assistant Professor, University College of Agriculture,

Bahauddin Zakariya University, Multan.

Dr. Muhammad Munir, former Assistant Professor, Department of Horticulture,

Faculty of Agriculture, Gomal University, Dera Ismail Khan.

Dr. Mohammad Safdar Baloch, Agronomist, Agricultural Research Institute,

Dera Ismail Khan.

Dr. Habib-ur-Rehman, Assistant Professor, Department of Horticulture, Faculty

of Agriculture, Gomal University, Dera Ismail Khan.

Dr. Muhammad Jamil Khan, Associate Professor, Department of Soil Science,

Faculty of Agriculture, Gomal University, Dera Ismail Khan.

(Jalal-ud-Din Baloch)

CONTENTS

TITLE Page No

ACKNOWLEDGEMENTS i CONTENTS ii LIST OF TABLES v LIST OF FIGURES vi ABBREVIATIONS xv ABSTRACT xvi CHAPTER 1 INTRODUCTION1.1 Importance of ornamental plants 1 1.2 Plant growth and development 2 1.3 Plants and their environment 31.4 Plants-light interaction 3 1.4.1 Solar-spectrum 4 1.4.2 Visible light 4 1.5 Discovery of photoperiodism 5 1.5.1 Photoperiodic response 6 1.5.2 Role of photoperiodism 7 1.6 Objectives of present study 8 CHAPTER 2 REVIEW OF LITERATURE 2.1 Light integrals / Light intensity / Irradiance 9 2.2 Photoperiod 39 2.3 Photoperiod-sensitivity 63 2.4 Plant height control 76 CHAPTER 3 MATERIALS AND METHODS3.1 Experimental location 111 3.2 Plant material and growing media 111 3.3 Plant nutrition and irrigation 112 3.4 Photoperiod controlled compartments 112 3.5 Light measurements device 113 3.6 Temperature measurements device 113 3.7 Plant growth substances 114 3.8 Data collection 114 3.8.1 Time to flowering 114 3.8.2 Plant height 114 3.9 Statistical procedures applied 115 3.10 Ambient environmental data 3.10.1 Day length (hours per day) 115 3.10.2 Solar radiation / photosynthetic active radiation 116 3.10.3 Monthly temperature (C) 117

CHAPTER 4 RESULTS AND DISCUSSION4.1 Effects of different sowing dates (ambient day length) on time to flowering

of important ornamental annuals 4.1.1 Introduction 120 4.1.2 Materials and Methods 121 4.1.3 Results 124 4.1.4 Discussion 128 4.2 Effects of different photoperiods on time to flowering of important

ornamental annuals 4.2.1 Introduction 138 4.2.2 Materials and Methods 139 4.2.3 Results 4.2.3.1 Facultative long day plants 141 4.2.3.2 Obligate long day plants 143 4.2.3.3 Facultative short day plants 144 4.2.4 Discussion 146 4.3 Effects of different light intensities on time to flowering of important

ornamental annuals 4.3.1 Introduction 173 4.3.2 Materials and Methods 175 4.3.3 Results 176 4.3.4 Discussion 179 4.4 Effects of different shade levels (light integrals) on time to flowering of

important ornamental annuals 4.4.1 Introduction 190 4.4.2 Materials and Methods 191 4.4.3 Results 193 4.4.4 Discussion 195

4.5 An appraisal of the use of reciprocal transfer experiments: Assessing the stages of photoperiod sensitivity in Pansy, Snapdragon, Petunia and Cosmos

4.5.1 Introduction 206 4.5.1.1 Analytical approach presented by Ellis et al. (1992) 207 4.5.1.2 Analytical approach presented by Adams et al. (2003) 210 4.5.2 Materials and Methods 213 4.5.3 Results 4.5.3.1 Pansy cv. Baby Bingo (LDP) 215 4.5.3.2 Snapdragon cv. Coronette (LDP) 215 4.5.3.3 Petunia cv. Dreams (LDP) 216 4.5.3.4 Cosmos cv. Sonata Pink (SDP) 216 4.5.4 Discussion 217 4.6 A comparative study on plant growth regulators and non-inductive

plant environment to control plant height of important ornamental annuals 4.6.1 Introduction 223 4.6.2 Materials and Methods 225 4.6.2.1 Effect of plant growth regulators on plant height 225 4.6.2.2 Effect of non-inductive environment on plant height 226 4.6.3 Results 227 4.6.3.1 Effect of plant growth regulators on plant height 227 4.6.3.2 Effect of non-inductive environment on plant height 229 4.6.4 Discussion 231 CHAPTER 5 SUMMARY 249 CHAPTER 6 CONCLUSION 253 LITERATURE CITED 255

LIST OF TABLES

Table No.

TITLE Page No.

4.1.1 Environmental detail of experiment 4.1 (2004-2005). 123 4.1.2 Environmental detail of experiment 4.1 (2005-2006). 124 4.2.1 Environmental detail of experiment 4.2 (March 1, 2005). 141 4.2.2 Environmental detail of experiment 4.2 (March 1, 2006). 141 4.3.1 Environmental detail of experiment 4.3 (October 1, 2005-2006). 176 4.3.2 Environmental detail of experiment 4.3 (October 1, 2005-2006). 176 4.4.1 Environmental detail of experiment 4.4 (Year 2006). 193 4.4.2 Environmental detail of experiment 4.4 (Year 2007). 193 4.5.1 Environmental detail of experiment 4.5 (June 15, 2006). 215 4.5.2 Environmental detail of experiment 4.5 (June 15, 2007). 215 4.5.3 Effect of long days and short days on flowering time of Pansy

cv. Baby Bingo, Snapdragon cv. Coronette, Petunia cv. Dreams and Cosmos cv. Sonata Pink. Standard errors of means are shown in parenthesis.

217 4.5.4 The durations of the phases of photoperiod sensitivity of three

LD annual ornamentals, Pansy cv. Baby Bingo, Snapdragon cv. Coronette, Petunia cv. Dreams and one SD annual ornamental Cosmos cv. Sonata Pink. Values in parenthesis are the standard errors of the estimates of the parameters of the model fitted using the FITNONLINEAR directive of GenStat-8.

217 4.6.1 Environmental detail of experiment 4.6 (March 1, 2006). 227 4.6.2 Environmental detail of experiment 4.6 (March 1, 2007). 227

LIST OF FIGURES

Figure

No. TITLE

Page No.

3.1 Day length (h.d-1) recorded from dawn to sunset at weather station.

115

3.2 Average photosynthetic active radiation (PAR, MJ.m-2.d-1) recorded using solarimeters at weather station during the experimental year 2004-2007.

116 3.3 Monthly maximum, minimum and average temperature (C)

recorded using a hygrothermograph at weather station during the experimental year 2004-2005.

117 3.4 Monthly maximum, minimum and average temperature (C)

recorded using a hygrothermograph at weather station during the experimental year 2006-2007.

118 3.5 A cumulative graph showing an average monthly temperature

(C) during the experimental year 2004-2007.

119 4.1.1(A,B) Effect of different sowing dates (day length) on the flowering

time of (A) Zinnia cv. Lilliput and (B) Sunflower cv. Elf. Each point represents the mean of 6 replicates. Vertical bars on data points (where larger than the points) represent the standard error within replicates whereas vertical bar (SED) showing standard error of difference among means.


time of (A) French Marigold cv. Orange Gate and (B) African Marigold cv. Crush. Each point represents the mean of 6 replicates. Vertical bars on data points (where larger than the points) represent the standard error within replicates whereas vertical bar (SED) showing standard error of difference among means.


time of (A) Cockscomb cv. Bombay and (B) Cosmos cv. Sonata Pink. Each point represents the mean of 6 replicates. Vertical bars on data points (where larger than the points) represent the standard error within replicates whereas vertical bar (SED) showing standard error of difference among means.


time of (A) Moss Rose cv. Sundance and (B) Pansy cv. Baby Bingo. Each point represents the mean of 6 replicates. Vertical bars on data points (where larger than the points) represent the standard error within replicates whereas vertical bar (SED) showing standard error of difference among means.

133

4.1.5(A,B) Effect of different sowing dates (day length) on the flowering time of (A) Snapdragon cv. Coronette and (B) Petunia cv. Dreams. Each point represents the mean of 6 replicates. Vertical bars on data points (where larger than the points) represent the standard error within replicates whereas vertical bar (SED) showing standard error of difference among means.


time of (A) Pot Marigold cv. Resina and (B) Annual Phlox cv. Astoria Magenta. Each point represents the mean of 6 replicates. Vertical bars on data points (where larger than the points) represent the standard error within replicates whereas vertical bar (SED) showing standard error of difference among means.


time of (A) Cornflower cv. Florence Blue and (B) Oriental Poppy cv. Burning Heart. Each point represents the mean of 6 replicates. Vertical bars on data points (where larger than the points) represent the standard error within replicates whereas vertical bar (SED) showing standard error of difference among means.

136 4.1.8(A,B) Effect of different sowing dates (daylength) on the flowering

time of (A) Flax cv. Scarlet Flax and (B) Nemesia cv. Safari. Each point represents the mean of 6 replicates. Vertical bars on data points (where larger than the points) represent the standard error within replicates whereas vertical bar (SED) showing standard error of difference among means.

137 4.2.1(A,B) Effect of different photoperiods on the flowering time of (A)

Moss Rose cv. Sundance and (B) Pansy cv. Baby Bingo. Each point represents the mean of 6 replicates. Vertical bars on data points (where larger than the points) represent the standard error within replicates whereas vertical bar (SED) showing standard error of difference among means.


Snapdragon cv. Coronette and (B) Petunia cv. Dreams. Each point represents the mean of 6 replicates. Vertical bars on data points (where larger than the points) represent the standard error within replicates whereas vertical bar (SED) showing standard error of difference among means.


Annual Verbena cv. Obsession and (B) Pot Marigold cv. Resina. Each point represents the mean of 6 replicates. Vertical bars on data points (where larger than the points) represent the standard error within replicates whereas vertical bar (SED) showing standard error of difference among means.


Annual Phlox cv. Astoria Magenta and (B) Cornflower cv. Florence Blue. Each point represents the mean of 6 replicates. Vertical bars on data points (where larger than the points) represent the standard error within replicates whereas vertical bar (SED) showing standard error of difference among means.

152

4.2.5(A,B) Effect of different photoperiods on the flowering time of (A) Oriental Poppy cv. Burning Heart and (B) Flax cv. Scarlet Flax. Each point represents the mean of 6 replicates. Vertical bars on data points (where larger than the points) represent the standard error within replicates whereas vertical bar (SED) showing standard error of difference among means.


Zinnia cv. Lilliput and (B) Sunflower cv. Elf. Each point represents the mean of 6 replicates. Vertical bars on data points (where larger than the points) represent the standard error within replicates whereas vertical bar (SED) showing standard error of difference among means.


French Marigold cv. Orange Gate and (B) African Marigold cv. Crush. Each point represents the mean of 6 replicates. Vertical bars on data points (where larger than the points) represent the standard error within replicates whereas vertical bar (SED) showing standard error of difference among means.


Cockscomb cv. Bombay and (B) Cosmos cv. Sonata Pink. Each point represents the mean of 6 replicates. Vertical bars on data points (where larger than the points) represent the standard error within replicates whereas vertical bar (SED) showing standard error of difference among means.

156 4.2.9(A,B) Effect of different photoperiods on the rate of progress to

flowering (1/f) of (A) Moss Rose cv. Sundance and (B) Pansy cv. Baby Bingo. Each point represents the mean of 6 replicates. Vertical bars on data points (where larger than the points) represent the standard error within replicates.


flowering (1/f) of (A) Snapdragon cv. Coronette and (B) Petunia cv. Dreams. Each point represents the mean of 6 replicates. Vertical bars on data points (where larger than the points) represent the standard error within replicates.


flowering (1/f) of (A) Annual Verbena cv. Obsession and (B) Pot Marigold cv. Resina. Each point represents the mean of 6 replicates. Vertical bars on data points (where larger than the points) represent the standard error within replicates.


flowering (1/f) of (A) Annual Phlox cv. Astoria Magenta and (B) Cornflower cv. Florence Blue. Each point represents the mean of 6 replicates. Vertical bars on data points (where larger than the points) represent the standard error within replicates.


flowering (1/f) of (A) Oriental Poppy cv. Burning Heart and (B) Flax cv. Scarlet Flax. Each point represents the mean of 6 replicates. Vertical bars on data points (where larger than the points) represent the standard error within replicates.

161

4.2.14(A,B) Effect of different photoperiods on the rate of progress to flowering (1/f) of (A) Zinnia cv. Lilliput and (B) Sunflower cv. Elf. Each point represents the mean of 6 replicates. Vertical bars on data points (where larger than the points) represent the standard error within replicates.


flowering (1/f) of (A) French Marigold cv. Orange Gate and (B) African Marigold cv. Crush. Each point represents the mean of 6 replicates. Vertical bars on data points (where larger than the points) represent the standard error within replicates.


flowering (1/f) of (A) Cockscomb cv. Bombay and (B) Cosmos cv. Sonata Pink. Each point represents the mean of 6 replicates. Vertical bars on data points (where larger than the points) represent the standard error within replicates.

164 4.2.17(A,B) The relationship between the actual rate of progress to flowering

against those fitted by the flowering model (1 / f = a + bP) for (A) Moss Rose cv. Sundance and (B) Pansy cv. Baby Bingo grown under 8 (□), 11 (◊), 14 (○) and 17 (Δ) h.d-1 photoperiod. The sold line is the line of identity.


against those fitted by the flowering model (1 / f = a + bP) for (A) Snapdragon cv. Coronette and (B) Petunia cv. Dreams grown under 8 (□), 11 (◊), 14 (○) and 17 (Δ) h.d-1 photoperiod. The sold line is the line of identity.


against those fitted by the flowering model (1 / f = a + bP) for (A) Annual Verbena cv. Obsession and (B) Pot Marigold cv. Resina grown under 8 (□), 11 (◊), 14 (○) and 17 (Δ) h.d-1 photoperiod respectively. The sold line is the line of identity.


against those fitted by the flowering model (1 / f = a + bP) for (A) Annual Phlox cv. Astoria Magenta and (B) Cornflower cv. Florence Blue grown under 8 (□), 11 (◊), 14 (○) and 17 (Δ) h.d-1 photoperiod. The sold line is the line of identity.


against those fitted by the flowering model (1 / f = a + bP) for (A) Oriental Poppy cv. Burning Heart and (B) Flax cv. Scarlet Flax grown under 8 (□), 12 (◊), 14 (○) and 17 (Δ) h.d-1 photoperiod. The sold line is the line of identity.


against those fitted by the flowering model (1 / f = a + bP) for (A) Zinnia cv. Lilliput and (B) Sunflower cv. Elf grown under 8 (□), 11 (◊), 14 (○) and 17 (Δ) h.d-1 photoperiod. The sold line is the line of identity.


against those fitted by the flowering model (1 / f = a + bP) for (A) French Marigold cv. Orange Gate and (B) African Marigold cv. Crush grown under 8 (□), 11 (◊), 14 (○) and 17 (Δ) h.d-1 photoperiod. The sold line is the line of identity.

171

4.2.24(A,B) The relationship between the actual rate of progress to flowering against those fitted by the flowering model (1 / f = a + bP) for (A) Cockscomb cv. Bombay and (B) Cosmos cv. Sonata Pink grown under 8 (□), 11 (◊), 14 (○) and 17 (Δ) h.d-1 photoperiod. The sold line is the line of identity.

172 4.3.1(A,B) Effect of different light intensities on the flowering time of (A)

Moss Rose cv. Sundance and (B) Pansy cv. Baby Bingo. Each point represents the mean of 6 replicates. Vertical bars on data points (where larger than the points) represent the standard error within replicates whereas vertical bar (SED) showing standard error of difference among means.








Oriental Poppy cv. Burning Heart and (B) Flax cv. Scarlet Flax. Each point represents the mean of 6 replicates. Vertical bars on data points (where larger than the points) represent the standard error within replicates whereas vertical bar (SED) showing standard error of difference among means.





188

4.3.8(A,B) Effect of different light intensities on the flowering time of (A) Cockscomb cv. Bombay and (B) Cosmos cv. Sonata Pink. Each point represents the mean of 6 replicates. Vertical bars on data points (where larger than the points) represent the standard error within replicates whereas vertical bar (SED) showing standard error of difference among means.

189 4.4.1(A,B) Effect of different shade levels on the flowering time of (A) Moss

Rose cv. Sundance and (B) Pansy cv. Baby Bingo. Each point represents the mean of 6 replicates. Vertical bars on data points (where larger than the points) represent the standard error within replicates whereas vertical bar (SED) showing standard error of difference among means.

198 4.4.2(A,B) Effect of different shade levels on the flowering time of (A)












204

4.4.8(A,B) Effect of different shade levels on the flowering time of (A) Cockscomb cv. Bombay and (B) Cosmos cv. Sonata Pink. Each point represents the mean of 6 replicates. Vertical bars on data points (where larger than the points) represent the standard error within replicates whereas vertical bar (SED) showing standard error of difference among means.

205 4.5.1 Schematic representation (not to scale) of the response of time

from seedling emergence to first flowering (f) for a LDP transferred from LD to SD (────) and from SD to LD (--------) at various times from sowing if the period from sowing to first flowering comprises a photoperiod-sensitive phase (durations IL and IS in long- and short-days, respectively) sandwiched between two photoperiod-insensitive phases, namely a pre-inductive phase (duration a1) and a post-inductive phase (duration a3).

208 4.5.2(A,B) Schematic representation (not to scale) of the model for a LDP

transferred from LD to SD (────) and from SD to LD (--------) at regular intervals from seedling emergence to first flowering. The response of the plants being described by five developmental phases, a photoperiod-insensitive juvenile phase (a1), photoperiod-sensitive flower induction (PIL) and flower development (PdL) phases in LD, a photoperiod-sensitive phase for flowering in SD (PIS) and a photoperiod-insensitive flower development (a3) phase (from Adams et al., 2003).

212 4.5.3(A,B) Effect of transferring plants from LD (17h.d-1) to SD (8h.d-1) (○)

and from SD to LD () at regular intervals from seedling emergence, starting on 15th June 2006 of (A) Pansy cv. Baby Bingo and (B) Snapdragon cv. Coronette. The vertical bars (where larger than the points) represent the standard error within replicates. The solid lines show the fitted relationships (Table 4.5.4 for parameters estimates) for plants transferred from LD to SD and from SD to LD respectively.

221 4.5.4(A,B) Effect of transferring plants from LD (17h.d-1) to SD (8h.d-1) (○)

and from SD to LD () at regular intervals from seedling emergence, starting on 15th June 2006 of (A) Petunia cv. Dreams and (B) Cosmos cv. Sonata Pink. The vertical bars (where larger than the points) represent the standard error within replicates. The solid lines show the fitted relationships (Table 4.5.4 for parameters estimates) for plants transferred from LD to SD and from SD to LD respectively.

222 4.6.1(A,B) Effect of different plant growth regulators on plant height of (A)


235

4.6.2(A,B) Effect of different plant growth regulators on plant height of (A) Annual Verbena cv. Obsession and (B) Pot Marigold cv. Resina. Each point represents the mean of 6 replicates. Vertical bars on data points (where larger than the points) represent the standard error within replicates whereas vertical bar (SED) showing standard error of difference among means.










Cockscomb cv. Bombay and (B) Cosmos cv. Sonata Pink. Each point represents the mean of 6 replicates. Vertical bars on data points (where larger than the points) represent the standard error within replicates whereas vertical bar (SED) showing standard error of difference among means.

241 4.6.8(A,B) Effect of different duration of non-inductive environment

(shortday) on plant height of (A) Snapdragon cv. Coronette and (B) Petunia cv. Dreams. Each point represents the mean of 6 replicates. Vertical bars on data points (where larger than the points) represent the standard error within replicates whereas vertical bar (SED) showing standard error of difference among means.


(shortday) on plant height of (A) Annual Verbena cv. Obsession and (B) Pot Marigold cv. Resina. Each point represents the mean of 6 replicates. Vertical bars on data points (where larger than the points) represent the standard error within replicates whereas vertical bar (SED) showing standard error of difference among means.

243

4.6.10(A,B) Effect of different duration of non-inductive environment (shortday) on plant height of (A) Annual Phlox cv. Astoria Magenta and (B) Cornflower cv. Florence Blue. Each point represents the mean of 6 replicates. Vertical bars on data points (where larger than the points) represent the standard error within replicates whereas vertical bar (SED) showing standard error of difference among means.


(shortday) on plant height of (A) Oriental Poppy cv. Burning Heart and (B) Flax cv. Scarlet Flax. Each point represents the mean of 6 replicates. Vertical bars on data points (where larger than the points) represent the standard error within replicates whereas vertical bar (SED) showing standard error of difference among means.


(longday) on plant height of (A) Zinnia cv. Lilliput and (B) Sunflower cv. Elf. Each point represents the mean of 6 replicates. Vertical bars on data points (where larger than the points) represent the standard error within replicates whereas vertical bar (SED) showing standard error of difference among means.


(longday) on plant height of (A) French Marigold cv. Orange Gate and (B) African Marigold cv. Crush. Each point represents the mean of 6 replicates. Vertical bars on data points (where larger than the points) represent the standard error within replicates whereas vertical bar (SED) showing standard error of difference among means.


(longday) on plant height of (A) Cockscomb cv. Bombay and (B) Cosmos cv. Sonata Pink. Each point represents the mean of 6 replicates. Vertical bars on data points (where larger than the points) represent the standard error within replicates whereas vertical bar (SED) showing standard error of difference among means.

248

ABBREVIATIONS

LD

SD

LDP

SDP

DNP

cv

cvs

P

PAR

PPFD

h

h.d-1

f

1/f

a1

PIL

PdL

PIS

PdS

a3

r2

d.f.

PGRs

ppm

mL/ml

a.i.

mg

nm

Long days

Short days

Long day plant(s)

Short day plant(s)

Day neutral plant(s)

Cultivar

Cultivars

Mean photoperiod (h.d-1)

Photosynthetic active radiation (MJ.m-2.d-1; total solar radiation)

Photosynthetic photon flux density (µmol m-2 s-1 or mol m-2 d-1)

Hours

Hour per day

Days to first flowering

Rate of progress to flowering

Photoperiod-insensitive juvenile phase (d)

Photoperiod-sensitive flower induction phase in long days (d)

Photoperiod-sensitive flower developmental phase in long days (d)

Photoperiod-sensitive inductive phase in short days (d)

Photoperiod-sensitive flower development phase in short days (d)

Photoperiod-insensitive flower developmental phase in LD and SD (d)

Regression coefficient

Degree of freedom

Plant growth regulators

Part per million (mg/L)

Millilitre

Active ingredient

Milligram

Nanometre

Manipulation of Light Environment to Control Flower Development and

Plant Height of Annual Ornamentals

Jalal-ud-Din Baloch, Muhammad Qasim Khan and Muhammad Zubair

ABSTRACT

The effects of light environment on flowering and plant height control in annual

ornamentals such as Seeds of Moss Rose (Portulaca grandiflora L.) cv. Sundance,

Pansy (Viola tricolour hortensis L.) cv. Baby Bingo, Snapdragon (Antirhinum

majus L.) cv. Coronette, Petunia (Petunia hybrida Juss.) cv. Dreams, Annual

Verbena (Verbena hybrida L.), Pot Marigold (Calendula officinalis L.) cv.

Resina, Annual Phlox (Phlox drummondii L.) cv. Astoria Magenta, Cornflower

(Centaurea cyanus L.) cv. Florence Blue, Oriental Poppy (Papaver orientale L.)

cv. Burning Heart, Flax (Linum usitatissimum L.) cv. Scarlet Flax, Zinnia (Zinnia

elegans L.) cv. Lilliput, Sunflower (Helianthus annuus L.) cv. Elf, French

Marigold (Tagetes Patula L.) cv. Orange Gate, African Marigold (Tagetes erecta

L.) cv. Crush, Cockscomb (Celosia cristata L.) cv. Bombay, Cosmos (Cosmos

bipinnatus Cav.) cv. Sonata Pink were investigated at the Agricultural Research

Institute, Dera Ismail Khan, N.W.F.P. Pakistan during 2004 and 2007.

Present research findings expand the duration of growing period for both LDPs and

SDPs in their own responsive environment, which can also be extended by raising

these cultivars at later dates. Flowering time can be extended by controlling the

photoperiod environment. LDPs grown under SD environment took long time to

flower. Therefore, non-inductive environment (SD) lengthened the juvenile phase.

Similarly, SDPs grown under LD environment took more time to flower as non-

inductive environment (LD) stretched the duration of juvenile phase. By

combining the findings of experiments one and two plant scheduling technique for

year-round production can be efficiently used in ornamental annuals.

Year-round production of ornamental annuals can be obtained by incorporating

light integral with the day length. LDPs grown under low light intensity (42 and 45

µmol.m-2.s-1) or received low light integrals (40% shade) enhanced flowering

induction time. Similarly, flowering time can also be extended if SDPs grown

under high light intensity (92 and 119 µmol.m-2.s-1) or received high light integrals

(0 and 20% shade).

The duration of photoperiod-sensitive phases of the Pansy (LDP), Snapdragon

(LDP), Petunia (LDP) and Cosmos (SDP) varied with genotype. Pansy, Petunia

and Cosmos had 15-16 days whereas Snapdragon had 30 days long juvenile phase.

However, photoperiod-sensitive phase under inductive environment and

photoperiod-insensitive phase under inductive and non-inductive environments are

lengthened than the juvenile phase.

Use of plant growth regulators [A-Rest (30 ppm.L-1), Bonzi (30 ppm.L-1) and

Cycocel (1000 ppm.L-1)] significantly reduced plant height as compared to control

plants. On the other hand, plants placed for a short duration (2 weeks) under non-

inductive environment also reduced plant height. However, if taller plants are

required then this duration can also be extended up to 8 weeks to obtain maximum

plant height. This technique can be incorporated with the appropriate photoperiod

to obtain early, mid and late flowering along with an appropriate plant height in

accordance with the consumers’ choice.

CHAPTER 1

INTRODUCTION

1.1 Importance of ornamental plants

Ornamental plants including annuals have a wide spectrum of uses in

environmental management; the most obvious are direct effect on the ecological

position of human being. The use of ornamental horticulture is the functional and

aesthetic integration of people, building and site, using plant and space as its main

tool. The necessity of it in landscape architecture is for positive control of the fast

changing landscape for the future (Simpson and Ogorzaly, 2001). There are few

cities in Pakistan where ornamental plants are used functionally for environmental

improvement including Islamabad, Karachi, Lahore, Faisalabad, Peshawar and

Quetta. However, small gardens and parks also beautify the environment in small

towns.

Ornamental plants can also be used as cover mat on eroded areas (such as bedding

plants), they help in eliminating dust, and they reduce glare, air and noise pollution

and heat build up (Harrison, 1990; Hirschhorn and Oldenburg, 1991). They

provide good location for adventure parks, children playing ground, rest area and

other social events. Ornamental plants also serve as complementor, attractors,

emphasizers, diverters, indicators, and provide aesthetic function by creating

attractiveness for human activities.

The habit of using ornamental plants functionally for environmental improvement

is yet to be employed meaningfully in developing countries including Pakistan.

Most growers in Pakistan believe in cultivating the agronomic and vegetable crops

rather than to cultivate ornamental plants on extensive area. It is well obvious that

the growers of ornamental plants including annuals in USA, UK, Holland, France

and Germany are earning more than the agronomic crops which gives us a clear

beneficial vision of this industry (Anonymous, 1985; Anonymous, 2007b).

Pakistan is also exporting ornamentals to France, South Korea and Gulf countries

and earning foreign exchange (per se). Limited contemporary knowledge of

marketing and plant environment are main reasons due to which our growers are

behind their targets.

Annual ornamental plants provide a display for a limited period therefore there is

relatively short market season and inconsistency in the supply of these crops to the

market owing to various environmental factors (Pearson et al., 1994). If the crops

mature early or late, it will be wasted. Therefore, there is an intense need to

understand how plant environment (photo-thermal) affects the duration (flowering)

of annuals and how this can be modified to regulate the supply of these flowering

crops to the market (Pearson et al., 1994) which would be most beneficial for the

growers involved in this business. In the present study an attempt is made to show

that annual ornamentals can be grown at different dates and their time to flowering

can also be controlled by manipulating environmental factors such as light

duration, light intensity and light integrals. Consumers’ choice of plant height is

also varied with different regions therefore an attempt has been made to compare

chemical height control method with that of environmental control one. However,

present research experiments explore more scientific information about plant and

their environment, which could be applied to get maximum benefits by the

ornamental industry.

1.2 Plant growth and development

The flowering plants (angiosperms) go through a phase of vegetative growth

(juvenile phase) producing stem and leaves and a flowering phase (reproductive

phase) where they produce the organs for sexual reproduction (floral parts). In

‘annuals’, such as moss rose, pansy, snapdragon, petunia, calendula, phlox,

cornflower, poppy, flax, nemesia, zinnia, sunflower, marigolds, cockscomb and

cosmos the vegetative phase begins with germination of the seed. Flowering

follows and ends with the senescence and death of the plant. In ‘biennials’, such as

radish, carrot, turnip the vegetative phase takes up the first year; flowering

followed by and the death occurs in second year. In ‘perennials’, like trees and

shrubs flowering typically occurs year after year when conditions are appropriate

(Opik and Rolfe, 2005).

Vegetative growth of the shoot occurs at the apical meristem. The secondary

meristems or lateral buds are formed in the axils of the leaves and form branches.

After the completion of vegetative phase plants perceive the stimulus with the help

of environmental signals (photoperiod and/or temperature) or plant hormone

(gibberellin) and enter into the reproductive phase (Srivastava, 2002; Opik and

Rolfe, 2005).

1.3 Plants and their environment

Plants interact with their environment in numerous and diverse ways. Sometimes

these ways are not immediately apparent to the casual observer; yet, deeper study

of these interactions opens an impressive view of how the members of the plant

kingdom cope with constraints of the environment. Plant growth is greatly affected

by the environment. If any environmental factor is less than ideal, it limits plant's

growth. In other cases, environmental stress weakens a plant and makes it more

susceptible to disease or insect attack (Thomas and Vince-Prue, 1997; Opik and

Rolfe, 2005; Erwin, 2006).

Environmental factors that affect plant growth include light,

temperature, water, humidity, and nutrition. It is important to

understand how these factors affect plant growth and

development. With a basic understanding of these factors, the

growers may be able to manipulate plant environment to meet

their needs, whether for increased leaf, flower, or fruit production.

By recognizing the roles of these factors, the growers can easily

diagnose plant problems caused by environmental stress (Leclerc

and Jacobs, 2000; Opik and Rolfe, 2005; Erwin, 2006).

1.4 Plant-light interaction

A complete description of the light incident on a plant requires the characterisation

of its intensity (photon or energy irradiance), duration (photoperiod), quality

(spectral composition), and direction (relative location of source, and degree of

scattering). Light is both a source of energy and a source of information for green

plants. It is a source of energy for photosynthesis, and a source of information for

photoperiodism (night/day length), phototropism (light direction), and

photomorphogenesis (light quantity and quality). Plants both affect and are

sensitive to light quality and quantity. In other words plants both generate and

perceive light signals. Several photoreceptors are involved in the perception of

these signals, which are used by plants to gather positional and size information

about other neighbouring plants. The sensitivity of plants to light provides them

with the sense of vision (Thomas and Vince-Prue, 1997; Opik and Rolfe, 2005;

Erwin, 2006).

Other environmental signals, not related to neighbours, are dark/light

transitions such as those occurring at the soil surface, and those related to

day/night length. Photoreceptors are also involved in the perception of these

signals. Responses of plants to light quality and quantity can be studied at different

scales. Whole plants respond to shading and/or neighbours with increased stem

elongation rates, increased area of individual leaves, altered shape of leaf blades,

more horizontal leaf blades, and more vertical stems, branches or tillers, increased

apical dominance, changes in chemical composition such as mineral nutrients,

anthocyanins, chlorophylls and other metabolites (Wilkinson, 2000).

In a canopy, either closed or sparse, plants adjust their growth and development in

response to their sensing of neighbouring vegetation. The responses to alterations

in light quality produced by neighbours can occur even before any shading takes

places. The ‘shade-avoidance’ response decreases the size variability between

individuals in a canopy and causes a more even sharing of resources between

individuals i.e. photomorphogenic responses can increase the uniformity of plants

growing within a canopy. Another response to light quality is the timing of seed

germination (Ballare´, 1999; Opik and Rolfe, 2005).

1.4.1 Solar-spectrum

Sunlight (direct beam) has a more or less continuous spectrum in the visible,

infrared and ultraviolet-A range. In this range the spectrum is similar to the

emission spectrum of a black body at 5800 K, except for a few valleys caused by

absorption bands of water, oxygen and carbon dioxide. The peak of the sunlight

spectrum shifts towards red (longer wavelength) when the sun is at a low elevation

angle (near the horizon). The transition from darkness under the soil to exposure to

white light after emergence initiates de-etiolation: hypocotyl growth slows down or

stops, cotyledons expand and unfold, and the apical hook opens gene expression

(Opik and Rolfe, 2005).

1.4.2 Visible light

When light impinges on a leaf, some of it is reflected, some is transmitted and the

rest is absorbed. Light of different wavelength is affected differently. Reflected and

transmitted light is scattered (as opposed to mirror reflection). Absorptance in the

‘Photosynthetically Active Range’ (PAR, 400-700 nm) is very high in young fully

expanded leaves (80% to 95% of the incident light). Far-red light is not absorbed

by leaves, approximately half of it is reflected and the rest is transmitted (and

scattered). As not only leaves and cotyledons, but also growing internodes and

hypocotiles can sense the light environment. The quality of light incident on both

horizontal and vertical surfaces is significant for plants (Thomas and Vince-Prue,

1997; Opik and Rolfe, 2005).

1.5. Discovery of photoperiodism

Photoperiodism is the initiation of flowering based on the relative amounts of

darkness and light in a 24-hour period (Thomas and Vince-Prue, 1997; Erwin,

2006). Scientists first linked the onset of flowering to day length in the 1920s while

experimenting with soybeans and tobacco. During one experiment, plots of

soybeans were planted at two-week intervals throughout the spring and early

summer. Surprisingly, all of the plants flowered at approximately the same time,

no matter what their age. Based on this result, scientists postulated that an

environmental factor was triggering the flowering. Further experiments on tobacco

also supported this explanation. Most tobacco plants flower during the summer.

However, around 1920, a mutant appeared in a field of tobacco. The plant had

unusually large leaves and grew to an enormous height without ever flowering.

This new variety was named ‘Maryland Mammoth’. The researchers took cuttings

of this new variety and grew them in a greenhouse, where they would be protected

from frost. These cuttings flowered in December even though at that time they

were only half as tall as the field-grown specimen. Plants grown from this mutant's

seed also flowered in the winter (Garner and Allard, 1920).

Previously published work revealed that the flowering was related to day length, or

the number of hours of light the plants received. Scientists termed this

phenomenon photoperiodism and categorized plants as longday (LD), shortday

(SD), or day-neutral (DN). The perception of day length by the plant involves the

photomorphogenetic light sensor, phytochrome (Thomas and Vince-Prue, 1997).

Although it is the duration of the dark period in each diurnal cycle, which is of

paramount importance, it is conventional to describe photoperiodic responses in

terms of day length. Three main categories of response are recognised: photoperiod

insensitive or day neutral plants (DNPs), and then the two types of photoperiod

sensitive plants, short day plants (SDPs) which require long nights and long day

plants (LDPs) which require long days (short nights). In addition, within both

SDPs and LDPs there are species with obligate or absolute or qualitative responses

to photoperiod (flowering does not occur without the extension (in LDPs) or

reduction (in SDPs) of the duration of photoperiod) and others with quantitative or

facultative responses (flowering occurs without photoperiod but extension (in

LDPs) or reduction (in SDPs) of the duration of photoperiod hasten flowering).

Therefore, the ecological essence of photoperiodic responses is in the timing of

biological events (circadian rhythm) (Thomas and Vince-Prue, 1997; Taiz and

Zeiger, 2002).

Eventually, scientists discovered that it was actually the hours of uninterrupted

darkness that triggered flowering, rather than the hours of light. Experiments

showed that even brief flashes of light during the dark period of the cycle could

interfere with flower development - a discovery that we use to our advantage when

growing some plants, such as poinsettias, petunia, chrysanthemum, antirrhinum

etc. Despite this new understanding of photoperiodism, the terms long- and short-

day, which refer to hours of light rather than darkness, are still commonly used.

1.5.1 Photoperiodic response

Plants are able to measure, and respond to, the relative lengths of day and night. So

they must have some capacity to "count" the number of hours. Scientists have

determined that a plant's leaves are responsible for doing the counting. Leaves

contain a light-sensitive protein pigment called phytochrome. This pigment occurs

in two stable forms, one sensitive to visible red light called P660, (also called Pr),

one sensitive to far-red light - P730 (also called Pfr) on the edge of the visible

spectrum. Pr has an absorption peak at 660nm (red light) and Pfr has an absorption

peak at 730nm (far red light). Red light is not only absorbed by Pr, red light also

converts Pr to Pfr. The same is true for far red light and Pfr. Far red light converts

Pfr to Pr. The pigment that causes biological responses in plants is Pfr. A pigment

molecule can convert from one form to the other, depending on the type of light it

receives. In total darkness, however, the far-red sensitive form slowly reverts to the

other form. The length of total darkness, then, determines the ratio of the two

forms ((Thomas and Vince-Prue, 1997; Leclerc and Jacobs, 2000; Taiz and Zeiger,

2002).

Because of the mixture of red and far red light in sunlight, plants end their day with

about 60 percent Pfr and 40 percent Pr. During the night some of the Pfr slowly

converts to Pr and some of the Pfr just breaks down. Both these processes result in

a declining percentage of Pfr during the night. A high level of Pfr promotes

blooming in the long day (short night) plants. These must end their night with a

relatively high level in order to bloom. A high level of Pfr inhibits blooming in the

short day (long night) plants. These must end their night with a relatively low level

in order to bloom (Taiz and Zeiger, 2002).

This is how plants "count" the number of hours of darkness. And it is because of

phytochrome's ability to convert from one form to another that the plant is able to

detect when any type of light breaks the dark period. Only when a plant's darkness

requirement is met, the leaves release certain plant growth regulators / substances.

The substances travel from the leaves through the stem to the apical buds,

stimulating some of those buds to switch from leaf to flower production (Thomas

and Vince-Prue, 1997; Taiz and Zeiger, 2002).

1.5.2 Role of photoperiodism

It is noticeable that flowers are the reproductive structures responsible for

producing seeds and photoperiod regulates the time of flowering in a particular

plant. Here the question arises that why the timing of flowering might be important

to a plant? The few possibilities are:

Timing must be such that other plants of the same species are flowering at

the same time, encouraging cross-pollination for seed setting.

The plant should flower when its pollinators are active for fertilization.

The plant should flower early enough in the season for seeds to ripen and

disperse before the cold weather sets in.

Therefore photoperiodism is a way that plants can "tell time," and ensure that

flowering occurs on schedule. Scientists believe that this timing is in response to

photoperiod rather than being based on weather conditions or other environmental

factors. So what about those plants that don't employ photoperiodism to determine

when to flower? Another factor that influences the onset of flowering is

vernalization (temperature). The promotion of flowering by a cold treatment given

to the imbibed seed or young plant is the simplest definition of vernalization

(Thomas and Vince-Prue, 1984; Thomas and Vince-Prue, 1997; Taiz and Zeiger,

2002). However, not all plants can be vernalized as seed. In some species, young

plants attain a certain size before becoming sensitive to chilling (low temperature).

For example, Hyoscyamus niger becomes sensitive to low temperatures 10 days

after germination (Sarkar, 1958).

1.6 Objectives of present study

Followings are some salient objectives of the present studies:

To determine an applied possibility of plant scheduling in various annuals

under natural day length.

To observe flowering response of ornamental annuals under different

photoperiods environment.

To study the flowering response of ornamental annuals under different light

intensities.

To examine the flowering response of ornamental annuals under different

shade levels (light integrals).

To assess different phases of photoperiod-sensitivity of pansy, snapdragon,

petunia and cosmos using reciprocal transfers from inductive to non-

inductive environment and vice versa.

To control plant height of various ornamental annuals by manipulating

plant growth substances and light environment.

CHAPTER 2

REVIEW OF LITERATURE

2.1 Light integrals / Light intensity / Irradiance

Sandhu and Hodges (1971) studied the effects of temperature, photoperiod, and

light intensity on flowering and seed set several diverse strains of Cicer arietinum

L. Plants were grown in 15, 22.5, and 30°C conditions at about 16 and 28 kilolux.

Generally, plants in the high light intensity, 16-hour photoperiod, and at 22.5°C,

produced more flowers and seed than did other treatment combinations. Some

strains produced flowers and set seed under short photoperiods and may have

potential in breeding chickpea cultivars with wider environmental adaptability.

Hurd (1973) planted young tomato plants (cv. Minibelle) in plant growth cabinets

in 575 kJ m-2 (400–700 nm) daily radiation. Plants grown in an 8 h day were then

compared with those in which 10% of the radiation was taken from the main 8 h

light period and supplied over the next 8 h period. After 41 days from sowing the

16 h day plants had almost twice the dry weight of those in short days and a 55%

greater leaf area. Net assimilation rate, relative growth rate and relative leaf area

growth rates were all greater in long days, although the differences in growth

diminished with time. The long-day treatment also increased the proportion of dry

weight in the leaves, a function, which is usually relatively stable in different

environments. The beneficial effect of the long days may arise from a reduction in

night respiration, or an increase in rate of photosynthesis through the observed

increase in chlorophyll content. The 8 h light periods resulted in flower initiation

one or two nodes lower than the 16 h period so that the cultivar is a quantitative

short-day plant.

Sedgley and Buttrose (1978) studied the effects of light and temperature on

flowering and pollen tube growth in watermelon [Citrullus lanatus (Thunb.)

Matsum. and Nakai, cv. Early Yates] plants grown in controlled environment

cabinets. All female flowers were pollinated in one group of plants; none was

pollinated in the other group. Temperature increase from 25°C to 35°C with

daylength of 14 h and light intensity of 32 klx caused increase in flower number per

plant, proportion of male flowers, ovary length and diameter, ovule number per

ovary, rate of pollen tube growth and percentage of penetrated ovules at 24 hand 48

h after pollination. Very few flowers were produced at 40 °C, but there was a high

proportion of male flowers. Increase in daylength from 14 h to 24 h at 25°C with

light intensity of 32 klx also increased number of flowers per plant, ovary length

and diameter and number of ovules per ovary but sex expression and rate of pollen

tube growth were unaffected. Reduction in daylength from 14 h to 8 hat 25°C and

light intensity of 32 klx and reduction in light intensity from 32 klx to 8 klx at 25°C

and 14 h daylength both produced an increase in the percentage of immature

ovules. The presence of fruit on the vine resulted in fewer flowers per plant and in

reduced ovary length and diameter under all conditions tested.

Cockshull (1979) observed that short-day plant Chrysanthemum morifolium cv.

Polaris initiated flower buds in all irradiances of continuous light from 7.5 to 120

W m–2. As the irradiance increased, the transition to reproductive development

began earlier and the number of leaves initiated before the flower bud was reduced.

The autumn-flowering cultivars Polaris and Bright Golden Anne, and the summer-

flowering Golden Stardust were also grown in continuous light at different

temperatures; all initiated flower buds at temperatures from 10 to 28°C but only the

buds of Golden Stardust developed to anthesis and then only at 10 and 16°C.

Flower initiation began earliest at 16–22°C, and the number of leaves formed

before the flower bud was increased at 28°C. Golden Stardust was exceptional in

that the number of leaves formed was also increased at 10°C. Axillary meristems

adjacent to the terminal meristem initiated flower buds rapidly at 10°C but not at

28°C in all three cultivars. These results are discussed in relation to the

autonomous induction of flower initiation and the effects of the natural

environment on flowering of chrysanthemum.

De Jong (1981) reported that Chrysanthemum morifolium seedlings and cuttings

from those seedlings were grown to flowering at 17°C, short days (8 h) and two

levels of irradiance (10 and 30 W m–2). The cuttings flowered more readily than

the seedlings at both irradiances; especially at 10 W m-2 many seedlings remained

vegetative. The delay in flowering of the seedlings was accompanied by a higher

number of leaves produced before flowering. The number of leaves produced by

the seedling in excess of the number of leaves produced by the cutting from that

seedling varied considerably between genotypes. The correlations between

seedlings and the corresponding cuttings for days to flowering and number of

leaves were low but generally significant. It is concluded that cuttings are preferred

over seedlings in breeding programmes that aim at developing chrysanthemums for

low light winter production.

Havelange and Bernier (1983) reported that, in the apex of plants exposed to a

single short day at high irradiance, some changes occur that are normally observed

during the transition to flowering (full evocation), e.g., elevated soluble sugar and

starch levels, increased numbers of mitochondria and changed nucleolus structure.

These changes are of similar magnitude and follow the same sequence as the

corresponding changes during full evocation. Other changes, normally associated

with full evocation, e.g., increased mitotic activity, are not caused by one short day

at high irradiance. This treatment thus produces only what we call "partial

evocation".

Tuyl and Kwakkenbos (1986) started a breeding program to obtain lily genotypes

that can be forced without applying additional light. Growth room experiments

showed considerable differences among eight lily cultivars in their response to

light. For the selection of lilies with a low light requirement both seedling and

induced mutation populations were tested under winter light conditions in the

greenhouse. Analysis of an incomplete diallel cross between nine cultivars showed

significant differences in general combining ability (GCA) for flower bud abortion

(including bud blasting and bud abscission) and leaf scorch. 'Enchantment' had the

highest positive GCA for bud abortion, indicating a high sensitivity to low light

conditions, while 'Uncle Sam' had the lowest GCA. Sensitivity to leaf scorch is

significantly increased by using 'Pirate' and 'Scout' as parents. 'Connecticut King'

was found to be a probable source of cytoplasmic male sterility. Male sterility is

associated with better response to low light conditions. Out of 726 plants of

mutated populations of 'Enchantment' and 'Connecticut King' grown under winter

light conditions, 16 plants were selected. These selections were tested on a clonal

basis under controlled climate conditions. The mutants of 'Enchantment' appeared

to be significantly less sensitive for bud blasting (abortion in an early stage), not

for bud abscission (abortion in a later stage). For the mutants of 'Connecticut King'

just the reverse was found.

Hicklenton (1987) reported that low levels of photosynthetically active radiation

(PAR) in winter daylight at northern latitudes (45°N) present an obstacle to year-

round greenhouse production of Gypsophila paniculata cv. 'Bristol Fairy'.

Supplemental PPF (93 μmol s-1m-2 supplied from high pressure sodium lamps from

2000-0700 h each day) applied for 42 or 63 days to plants, enhanced flowering and

vegetative growth in crops grown between September and February (fall) and

January and June (spring). In a second experiment, plants were grown in growth

chambers at either 8.8 (HPAR) or 3.2 (LPAR) Mol.m-2 day (24 hour irradiance). At

14-day intervals plants were transferred from HPAR to LPAR chambers and vice

versa. Flower buds were formed first on plants which received between 500 and

550 Molm-2 during the first 76 days in treatments. Thereafter, buds were initiated

within 8 to 10 days irrespective of cumulative PAR. Yield of flowers and

vegetative plant parts increased with cumulative PAR up to about 745 Mol.m-2

received over a 115-day period. Higher irradiances during early development were

most effective in improving yield.

Langton (1987) reported that, when all of the potential flowers of a

chrysanthemum spray are initiated as a result of short-day treatment, a long-day

interruption can be introduced to improve winter quality. To aid the timing of this,

two methods, apical dissection and light-integral monitoring, were assessed as

possible alternatives to the generally used 'calendar' approach. The test procedures

involved the transfer at intervals of plants of three widely grown cultivars,

Snapper, Snowdon and Pink Gin, from short-day to non-inductive, long-day

conditions to give a measure of the basic petal progression of commitment to

flowering that had occurred up to the time of transfer. There was a time lag of

some days between the irreversible commitment of lateral buds to flower and the

visual detection, using a microscope, of morphological changes indicating that

initiation had occurred. The stage of development of the terminal flower bud had,

therefore, to be relied on as an indicator of lateral bud commitment. However, this

relationship was too variable to be of practical value. Uncontrollable variation in

light receipt was found to limit severely the precision with which the speed of bud

initiation of a given cultivar could be judged. To improve the timing of

interruptions, empirical relationships between the time to induce all buds and the

average daily light (PAR) integral (and average daily total solar radiation integral)

were determined for each of the three cultivars. These relationships were then

tested by transferring plants from short days to continuous long days on the

predicted day and up to six days before and after. Promising results were obtained

with flower induction completed by the predicted date in all cases.

Grarper and Healy (1990) irradiated Petunia × hybrida Villm. `Red Flash' plants

for either 10 or 20 mol day1 photosynthetic photon flux (PPF) in growth chambers

using one of the following treatments: 175 µmol m-2 s-1 for 16 h, 350 µmol m-2 s-1

for 8 or 16 h or 350 µmol m-2 s-1 for 8 h plus 8 h incandescent day extension (5

µmol m-2 s-1 PPF). These four treatments were designed to examine the effects of

increased peak and total daily integrated PPF as well as increased photosynthetic

(Pn) period and photoperiod resulting from supplemental irradiance treatment of

seedlings. Previous seedling petunia research indicated a greater response to

supplemental lighting during expansion of the second true leaf. Therefore,

seedlings were sampled for analysis at the two leaf stage and also later at the four

leaf stage to examine effects at a later stage of growth.

Armitage (1991) reported that field-grown cut-flower species were subjected to full

sun or 55% or 67% shade treatments for 2 to 3 years. Plants grown in shade had

longer flower stems than those grown in ambient irradiance; however, yield (flower

stems per plant) was species-dependent. Yield of Centaurea americana Nutt. `Jolly

Joker', an annual speices, and Eryngium planum L., a perennial, declined linearly

with each reduction in irradiance. However, yield of Echinops ritro L. `Taplow

Blue', a perennial species, was higher in 55% shade than in ambient irradiance.

Yield of transplants and tubers of Anemone coronaria L. `De Caen' were not

affected by planting material (transplants or tubers). Plants grown under 67% shade

had the longest stems starting 3 weeks after the beginning of harvest and the

difference persisted for an additional 4 weeks regardless of planting material. A

quadratic decline in yield in three of four cultivars of Zantedeschia Spreng

occurred as shade increased, but yield was similar for ambient and 55% shade.

Scape length and spathe width increased as shade increased, although some

cultivars were more responsive than others.

Gislerod et al. (1993) studied the yield and quality of five different greenhouse

rose cultivars (Kardinal, Frisco, Jaguar, Kiss and Madelon) grown under four

different levels of supplementary light (130, 190, 250 and 370 μmolm-2s-1

photosynthetic photon flux density, PPFD) from September until June in a

greenhouse with normal and high electrical conductivity (EC) in the growing

medium. The highest light level contributed to a photosynthetic active radiation

during winter which exceeded the natural radiation during summer. Generally the

yield increased as the PPFD level increased from 130 to 250 or 370 μmolm-2s-1,

and this was the case during the whole period. The response of PPFD varied

between the cultivars and as an average the yield increased 18, 41 and 53% at 190,

250 and 370 μmolm-2s-1 PPFD, respectively, compared to 130 μmolm-2s-1. Raising

the EC in the growing medium from 2-3 to 4-6 mS cm-1 increased the yield by 9%

as a mean. For two cultivars it was an increase of 26%, while for one it was a

decrease of 8%. The quality of the roses increased with increasing PPFD by a

higher proportion of class one shoots by longer stems particularly during mid-

winter, and by an enhancement of the keeping quality. The content of macro

nutrient elements in the leaves decreased with increasing PPFD, while no effect of

the EC was found except for cv. Jaguar where the content of N and K was lower at

high compared to normal EC.

Seddigh and Jolliff (1994) determined the effects of photosynthetic photon fluxes

(PPF) before and after photoperiodic floral induction (PF1) on meadowfoam

growth and flowering. ‘Mermaid’ growth and flowering responses to PPF of 150,

300, 450, 600, 750, and 900 µmol m–2 s–1 were investigated in a controlled

environment. Treatments were initiated either 24 d before or at PF1. Increasing

PPF, both before and at PF1, reduced days to first flower, flowering duration, total

flowers produced per plant, flowers with bad stamens, and plant height and dry

weight at maturity. More flowers were produced when PPF treatments were

initiated 24 d before PF1 compared with those initiated at PF1. Light intensities

<450 µmol m–2 s–1 after PF1 appeared to result in slow stem growth, increased

potential number of flowering stems and flowers, and an exponential delay in

flowering. Conversely, PPF >600 µmol m–2 s–1 after PF1 enhanced flowering and

maturity, and decreased plant size, flower number, and duration of flowering. After

PF1, 450 to 600 µmol m–2 s–1 PPF appeared optimum for a balance of flower

production and plant growth in controlled environments. Higher PPF before PFI,

however, may increase the potential number of flowering stems and flowers, but it

did not substitute for long daylength required for floral induction. Results suggest

that in western Oregon low light intensity during fall and winter months may

contribute to excessive vegetative growth of Mermaid meadowfoam at the expense

of seed production.

Basoccu and Nicola (1995) examined the effects of different levels of

supplementary light (natural PAR, id. plus 4 or 8 hours of supplementary light at

150 μmol m-2s-1) and of different N supply in the nursery nutrient solution

(4,8,15,30,60 mmol l-1) on tomato (Lycopersicon esculentum Mill.) seedling

growth and yield. The supplementary lighting started at sunset. Each plant received

200 ml of N solution in 4 times during nursery growth. The seeds were sown in

plastic pots on February 25 and the young plants were transferred in plastic house

at the density of 4,1 plants m-2 on April 5 1992. Fruit harvesting began on June 8

and ended on July 31. All the data recorded in nursery and the Growth Rate values

calculated were significant. They showed a different role played by N level supply

depending on daylight length. Increasing the supplementary lighting (from 0 to

8hrs/day) at the seedling stage the early production increased only. It showed the

maximum value at 15 mmol l-1 N level, the minimum at 4 and 60 mmol l-1. As

regards the early production no interaction between N supply and light was found.

De Smedt et al. (1996) reported that leaf number of Clivia miniata Regel increased

significantly with higher temperature (20°C compared with 16 and 7°C).

Supplementary lighting (to reach a photoperiod of 16 h) during winter time had no

effect on leaf number but promoted leaf elongation, resulting in poorer plant

quality. The first flower bud was initiated after 12-13 leaves were formed,

regardless of temperature or light treatment; subsequent flower buds were initiated

after each set of four to five leaves. Higher temperatures hastened flower bud

development. However, scape elongation was insufficient. Supplementary lighting

hastened the latter process.

Takeno et al. (1996) studied flowering and the male sterility induced by short days

(SD) in Salsola komarovii Iljin (Chenopodiaceae) anatomically and

physiologically. A light-microscopic observation found that the male-sterile

flowers had traces of stamens. The development of stamens ceased at the last stage

of meiosis of pollen mother cells, and then vacuolated and degenerated. Flowering

occurred earlier, and the number of flowers increased with increasing irradiance

levels. On the other hand, the irradiance affected male sterility only slightly, and

most of the flowers were male sterile even under high irradiance. The results

indicate that irradiance interacts with photoperiod in different ways in regulation of

flowering and male sterility within the same species.

Wang (1996) selected Lilium longiflorum Thunb. 'Nellie White' plants when their

first flower buds reached 2 or 5 cm in length and sprayed with 2 mL of PBA at 0 or

500 mg.L-1, and then placed under 1440 or 60μmol.m-2.s-1 photosynthetic photon

flux (PPF) during flowering. PBA resulted in delayed anthesis and increased dry

matter accumulation in flowers under the high PPF but had no effect under the low

PPF. PBA did not decrease the severity of flower bud abortion under the low PPF.

Application of PBA induced the formation of numerous bulbils in the leaf axils.

Regardless of PPF, PBA-treated plants had less dry weight in the main bulbs than

the control plants.

Myster (1999) investigated interactions between a 2 h temperature alteration at the

end of the night, day extension light quality, photoperiod, and irradiance level on

plant height in B. × hiemalis. The effects of differences (DIF) between day (DT)

and night temperature (NT) on stem elongation rate were also studied. Compared

with a temperature increase from 18 to 24°C (18->24°C), a temperature drop of 19

to 13°C (19->13°C) decreased plant height when combined with fluorescent lamps

as day extension light quality of high red (R)/far red (FR) ratio both at 95 and at

190 µmol-2 s-1 PPFD. In combination with incandescent lamps with a low R/FR

ratio, temperature drop reduced height only under 190 µmol-2 s-1 PPFD at 16 h

photoperiod. Averaged across day extension light quality, a temperature drop

compared with a temperature increase decreased height at high irradiance level but

not at low level. Under high irradiance, height increased at 18->24°C with

increasing photoperiod from 8 to 16 h while plants treated with a temperature drop

had about the same height under 12 and 16 h photoperiods. Height was greater

under incandescent lamps than under fluorescent lamps, except at 12 h photoperiod

and 18->24°C. Under low irradiation, height increased with increasing photoperiod

from 12 to 16 h under fluorescent lamps but not under incandescent lamps. Stem

elongation rate increased as DIF between DT and NT increased. Plants grown

under 0 and positive DIF had a greater elongation rate during night than during

day, while no significant difference was observed in plants grown under negative

DIF. No significant differences in leaf area, dry weight and number of flower and

flower buds were found between temperature drop and temperature increase

treatments.

Yeh and Atherton (1999) studied the effects of total irradiance on growth and

flowering in cineraria cv. Cindy Blue grown under warm (mean 21°C) glasshouse

conditions. Efficiency of light conversion for leaf and shoot dry weight increase

were reduced from 0.08 to 0.02 as the mean daily light integral increased from 0.9

to 4.4 MJ m-2 day-1 but no significant difference in leaf area were associated with

this. Specific leaf area decreased exponentially from 0.07 to 0.02 m2g1 over the

cumulative irradiance range 23 to 127 MJ m-2 after the start of treatments and

thereafter remained stable. A light integral of 19.2 MJ m-2 were required for

initiation of one leaf in plants grown under a daily integral of 4.4 MJ m-2 day-1, as

compared with only 5.1 MJ m-2 day-1 required per leaf in plants grown at less than

0.9 MJ m-2 day-1. Neither chronological duration of juvenile development nor leaf

number below the flower was affected by irradiance. However, as the rate of leaf

initiation increased with irradiance up to 2.4 MJ m-2day-1 so the rate of progress to

flower visibility increased linearly with irradiance over the same range. This rate

then remained constant from 2.4 to 4.4 MJ m-2 day-1. Length of the main flowering

shoot decreased and the number of flowering shoots increased as irradiance

increased from 0.9 to 2.4 MJ m-2 day-1 and then remained unchanged by further

increases in irradiance.

Autio (2000) investigated the effects of photoperiod, supplementary light intensity

and daily supplementary light integral on gerbera (Gerbera × cantabrigensis

Lynch cvs. Estelle and Ximena) flowering in poor natural light conditions. The

plants were subjected to different photoperiods (12, 18 and 24 h), light intensities

(75, 112.5, 150 and 300 μmol/m2s-1 PAR) and supplementary lighting periods (12,

18 and 24 h). In all experiments the 12-h photoperiod produced the highest number

of inflorescences if the same daily supplementary light integral was used. Doubling

the daily light integral by extending the photoperiod to 24 h did not increase the

flower yield except in the case of 'Estelle' in one experiment. On the other hand, an

increase in the daily light integral by increased supplementary light intensity

affected strongly the number of inflorescences in the 12-h photoperiod. As the

quantity of gerbera flower yield is strongly affected by supplementary lighting

regimes, grower must be aware of that different distributions of same light energy

over one day may lead to a change of about 45 % in number of inflorescences. If

only the number of inflorescences is considered, a combination of short

photoperiod and high light intensity can be recommended.

Shikanori and Hiroshi (2000) examined the effects of reduced irradiance on growth

and flowering of amaryllis (Hippeastrum × hybridum cv. Apple Blossom). Low

irradiance delayed flowering and reduced flowering rate, whereas the leaves were

long. Measurement of fresh and dry weight of the flowers and space, leaves, bulb

and roots and their distribution to each organ suggested that the dry matter

accumulation in the bulb is suppressed by low irradiance; subsequently it causes

the abortion of flower buds or inhibition of flower bud development inside the

bulb.

Yeh and Wang (2000) studied the effects of irradiance on growth and net

photosynthesis in Adiantum raddianum cv. Fritz Luth grown under warm (26 ±

3°C) greenhouse conditions. Efficiency of light conversion for frond dry weight

increase was reduced from 0.0067 to 0.0016 as the mean daily light integral

increased from 1.3 to 6.7 MJ m-2 d-1. The maximum frond area and frond dry

weight were measured in plants grown in daily light integrals of 2.6 and 3.3 MJ m-2

d-1. Specific leaf area decreased exponentially from 0.046 to 0.032 m-2 g-1 over the

daily light integral from 0.6 to 6.7 MJ m-2 d-1. Rate of frond appearance was

linearly increased with increasing mean daily light integral from 0.6 to 6.7 MJ m-2

d-1 and a light integral of 4.2 MJ m-2 was required for appearance of one frond.

Pinnule thickness increased, and chlorophyll content decreased, as irradiance

increased from 0.6 to 6.7 MJ m-2 d-1. Numbers of fronds bearing sori increased

linearly with increasing irradiance up to 3.3 MJ m-2 d-1, beyond which the number

decreased. The fronds grown under 0.6-3.3 MJ m-2d-1 conditions had a

photosynthetic advantage over those under 5.9 and 6.7 MJ m-2d-1 at photosynthetic

photon flux (PPF) levels less than 50 mmol m22s21. Light compensation points

were near 15 mmol m-2 s-1 for fronds grown under 5.9 and 6.7 MJ m-2d-1, as

compared with 5.9 mmolm-2 s-1 for fronds preconditioned to lower irradiance levels

from 0.6 to 3.3 MJ m-2 d-1. Significantly fewer wilted fronds and better interior

performance quality were recorded in plants grown under daily light integrals from

0.6 to 2.6 MJ m-2 d-1.

Do et al. (2001) conducted an experiment using open-pollinated Theobroma cacao

seedlings whose female progenitor was SCA 6. The seedlings were submitted to

four irradiance levels (10, 25, 50 and, 100% of photosynthetically active radiation,

PAR) obtained through artificial shading. At 115 d after planting, the orthotropic

axes were cut off at 50 cm height and nitrogen treatments were applied at the rates

of 0, 3.5, 7.0 and 14.mM. After axillary bud break, the growth of only one flush

per plant as maintained on the orthotropic axis. At the F2 stage, mature leaves of

pre-flush 1 (PF-1) were used to measure gas exchanges, nitrate reductase activity

(NR), N-NO3- and chlorophyll concentrations. In general, increases in net

photosynthetic rates (Pn) were found with increase in N doses from zero to 7.0.mM

at all irradiance levels. From this dosage, Pn decreased at the 10 and 25% PAR

levels. The plants to which no N was added after cut off showed significantly

higher Pn values at 10 and 25% PAR and lower leaf and air temperatures in

relation to 50 and, 100% levels. The opposite was under 14.mM N where the

highest Pn values were obtained at 100 and 50% PAR levels. The highest value of

internal CO2 concentration (Ci) was obtained at 0.mM N, independently of

irradiance level. Values of Ci and stomatal conductance (gs), at 50% PAR, were

higher than the other measured values in all nitrogen doses. Conditions of

maximum irradiance did not favour higher gs, contributing to the reduction of

transpiration rates (TR). However, seedlings at 0.mM of N showed higher TR than

the others. There were increments in NR activity with the increase in nitrogen,

except at 100% PAR. This increase in activity was observed only from 0 to 3.5

mM N. The increase in N doses proportionally increased the stem N-NO3-

concentrations, mainly at the 10% PAR level. On the other hand, N-NO3-

concentration of PF-1 and pre-flush 2 (PF-2) leaves were higher than the

concentration of the remaining leaves after cut off, at the different PAR levels and

N doses evaluated. Leaves of PF-1 and PF-2 were responsible for the higher dry

mass accumulation in relation to stems, with the increase of irradiance levels and N

doses, except at 10% PAR. At this irradiance level, the accumulation of leaf and

stem dry mass increased from zero to 7 mM, decreasing afterwards.

Holcombe et al. (2001) discussed how light intensity (irradiance) and supplemental

lighting can affect flowering of seed-propagated bedding plants. This article is the

second article to focus on the same topic and provides additional information on

how the need for supplemental lighting varies in different parts of the country. In

addition, how species differ in how much light they can use is presented. Lastly,

how high day temperatures can affect photosynthetic rate and plant quality is

discussed. Future articles will show new results on how daylength affects

flowering of many bedding plants. Increased lighting, or irradiance, can reduce the

length of the juvenile period with some species, thereby reducing the time to

flower. We do not really understand how this occurs. Is juvenile period length

reduced by supplemental lighting because there is more food, or photosynthates,

available for flower induction? Photosynthesis is the process where a plant utilizes

sunlight and carbon dioxide in the air to make sugars, or food. Does supplemental

lighting alter the hormonal balance in plants? Answers to these questions could

help us to decrease, or increase, juvenile period length through breeding efforts and

environmental treatments. Juvenile period length varies in bedding plants. The

juvenile period of bedding plants can be nearly nonexistent or be as long as months

with some of the perennial species we grow in the industry. Additional lighting is

most effective in reducing juvenile period length on those species that have a

longer juvenile period such as perennials, seed geraniums, and ‘Purple Wave’

petunias. The juvenile period of most common bedding plants (herbaceous annuals

in temperate climates) is between 1 and 2 weeks. We measure the ‘maturity’ of a

plant by counting the number of leaves below a flower. In many cases, bedding

plants are mature when we can see 3 unfolded leaves on a seedling (1-2 weeks

after germination). We mention this because the length of the juvenile period of a

crop gives us some indication of the maximum amount we could shorten

production time! For instance, if the juvenile period on a ‘White Storm’ petunia is

nearly nonexistent, then providing supplemental lighting will reduce crop time

minimally. In contrast, if the juvenile period of ‘Purple Wave’ petunias is 2 weeks,

then it may be possible to reduce crop time by a maximum of 2 weeks by

shortening the juvenile period using lighting.

Islam and Willumsen (2001) studied the effects of different light conditions on

rooting and on subsequent growth and yield of flowering stems in Gypsophila

paniculata ‘Perfecta’ grown in greenhouse. Cuttings rooted in long day (LD) at

high daily light integral (HLI-LD) rooted faster than the cuttings rooted in LD at

low daily light integral (LLI-LD). Cuttings rooted in short day (SD) at low daily

light integral (LLI-SD) rooted at a similar speed as those in LLI-LD. The fresh and

dry weight of the aboveground part of the cuttings did not increase during first two

weeks. After 4 weeks, when more than 90% of the cuttings in all treatments were

well rooted, the mean fresh and dry weight of rooted cuttings under HLI-condition

had increased by nearly 100% and 75% respectively compared to initial weight,

while cuttings from the two LLI-treatments showed only about 40 % and 25 %

increase of fresh and dry weight respectively. Nearly doubling the DLI during

rooting promoted the rate of development until the visible bud stage in LD, but this

effect diminished in the plants given a period of SD after transplanting. Giving a

SD-treatment after rooting prolonged the time to visible bud and the first open

flower by 12-14 days, but significantly increased the leaf numbers, and number of

flowering shoots in the plants compared to the plants grown under continuous HLI-

LD. Photoperiod during rooting period did not influence the time to flower, length

of the main stem, or yield of flowering shoots.

Donnelly and Fisher (2002a) quantified the effect of supplemental lighting on

cutting production for 10 herbaceous annual cultivars. Stock plants of four cultivars

(Heliotropium arborescens Àtlantis', Petunia `Supertunia Sun Snow', Scaevola

aemula `New Wonder', and Verbena `Tapien Soft Pink') received ambient light

[average 6.2 mol m-2 d-1 photosynthetic photon flux (PPF) during the photoperiod],

or ambient light plus either 1.6 or 2.8 mol m-2 d-1 PPF from high-pressure sodium

(HPS) lamps for 11 hours. In a second experiment, the same four species plus six

other cultivars were grown under ambient light (average 7.9 mol m-2 d-1 PPF) or

ambient plus 1.9 mol m-2 d-1 PPF from HPS. The effect of HPS on the production

of cuttings varied greatly between species. Growth of Heliotropium was not

significantly affected by light level in either experiment. In the first experiment, the

addition of 1.6 mol m-2 d-1 PPF from HPS increased the number of Petunia

`Supertunia Sun Snow', Scaevola, and Verbena cuttings by 14%, 51%, and 12%.

The addition of 2.8 mol m-2 d-1 PPF from HPS, increased cuttings harvested from

these three species by 23%, 73%, and 22% respectively. In the second experiment,

Petunia `Supertunia Sun Snow', Scaevola, Aloysia triphylla (lemon verbena), and

Osteospermum `Lemon Symphony' had a positive cutting production response to

HPS (17% to 45% increase), whereas cutting numbers of other species

(Argyranthemum `Summer Melody', Lantana `Patriot Firewagon', Impatiens New

Guinea hybrid `Pedro', Petunia `Supertunia Blue Wren', and Verbena) were not

significantly affected by HPS. In both experiments, cutting quality (length, stem

calliper, fresh mass, and dry mass) and subsequent rooting of cuttings were not

significantly affected by light level.

Davies et al. (2002) determined the responses of flower stem quality attributes to

light and temperature in Sandersonia aurantiaca. There were five constant

temperatures of 15, 18, 21, 24 or 27°C, and three photosynthetic photon fluxes

(PPFs) of 700, 460, or 210 μmol m−2 s−1 with respective daily photon receipts

(DPRs) of 30.2, 19.4 or 9.1 mol m−2 per day. At flower harvest, 12 vegetative and

floral characteristics were measured. The longest flower stems were produced at 21

and 24°C, and a rise in temperature from 24 to 27°C resulted in the shortest stems.

However, flower numbers on the main stem increased linearly with temperature to

27°C. Temperature strongly influenced time to flower harvest with the interval

between shoot emergence and flower harvest being 52 days at 15°C and 24.5 days

at 27°C. Irradiance generally had larger effects than temperature on many

parameters, with most of the responses to irradiance being additive with

temperature. The low and intermediate PPF treatments (210 and 460 μmol m−2 s−1)

increased stem length but reduced the ability of the cut stems to stand erect without

bending. Low PPF also resulted in reduced flower numbers per stem and increased

flower abortion, particularly at the lower temperatures. The results suggest that the

problem of excessively short stems in summer is due to high temperature (>27°C)

and high irradiance (>700 μmol m−2 s−1), while stem weakness in winter is due to

low irradiance (<460 μmol m−2 s−1). The combination of 24 °C temperature and a

PPF of 700 μmol m−2 s−1 was recommended for producing long flower stems of the

highest quality. This combination would balance rapid flowering time, adequately

long and strong stems, and high flower numbers. In general, high quality flower

stem production requires relatively high irradiances (>460 μmol m−2 s−1) and

temperatures of 21–27°C.

Aya et al. (2003) generated the transgenic Arabidopsis plants over expressing g-

ECS to evaluate the relationship of GSH with the light-intensity-dependent

promotion of flowering. Flowering in the wild-type and transgenic plants was

promoted in a light-intensity-dependent manner, but in weak-light conditions, the

transgenics showed delayed flowering compared to the wild-type. As the light

intensity increased, the difference in flowering time between the wild-type and

transgenic plants reduced and, in strong-light conditions, almost disappeared.

These indicate that GSH suppresses the light-intensity-dependent promotion of

flowering. The expression levels of the flowering-time genes FT and AGL20/SOC1

in transgenic plants were not reduced compared to those in wild-type in both

strong- and weak-light conditions. Thus, it is not by inhibiting the expression of

these genes that GSH suppresses the light-intensity-dependent promotion of

flowering. The wild-type and transgenic plants grown in strong light showed

reduced expression levels of these genes compared to those in weak light.

Flowering-promotional effects of light were also observed in the mutants defective

in GI acting upstream of these genes. These suggest that the light-intensity-

dependent promotion of flowering associated with GSH is independent of these

flowering-regulating genes.

Jadwiga (2003) reported that oriental lily 'Laura Lee' was forced during wintertime

with or without supplementary lighting. Three fertilization levels were applied: N1

control, water without fertilizers and N2 and N3 contained Peters (15:11:29) at two

doses 0.8 and 1.6 g dm-3, respectively. The fertilization started in the third week

after planting. Supplementary lighting accelerated flowering about 3 weeks,

irrespective of the fertilization levels. It also improved plant quality expressed as

higher stem weight, better sturdiness, higher leaf area and better leaf coloration.

Supplementary lighting completely prevented flower bud abortion of 'Laura Lee'.

Plants grown with supplementary lighting showed higher nutrient demands.

Increased fertilization at low light levels led to higher accumulation of nutrients in

growing media.

Henriod et al. (2003) studied the response of floral development in two cultivars of

Metrosideros excelsa (Myrtaceae) to irradiance applied during floral induction to

test the hypothesis that floral initiation and flowering would be linearly and

positively correlated with this environmental factor. Plants were grown for 20

weeks at 174, 567, 961 or 1,355 µmol m-2 s-1 under conditions known to be

inductive for flowering (10 h photoperiod at 17/14°C), before transfer to a

common forcing greenhouse (mean 188C, 16 h photoperiod). Floral development

was examined histologically in buds that were initially in three size ranges

(<1.6.mm, 1.6-2.0.mm and >2.0.mm diameter) collected 13, 20 and 23 weeks after

the start of the experiment. Floral primordia were first observed after 20 weeks in

the highest three irradiance treatments. After 23 weeks, buds that were originally

1.6-2.0.mm in diameter in plants treated at 567 µmol m-2 s-1 had the highest

proportion of floral primordia (50percent). The lowest proportion of floral

primordia (6 percent) occurred in the 174 µmol m-2 s-1 treatment, and only in the

buds that were initially the largest. Floral meristem size after 23 weeks showed a

unimodal (non-linear) response to irradiance, a pattern reflected in the number of

inflorescences that reached anthesis after 31 weeks, both peaking at close to 567

µmol m-2 s-1. Some buds that initially contained floral primordia underwent

reversion to vegetative growth, possibly as a result of unfavourably high

temperatures during the time when organogenesis would have occurred. Most

inflorescences occurred in buds that were initially in the intermediate and largest

bud size ranges. Carbohydrate concentrations showed a positive linear response to

irradiance, whereas chlorophyll showed a significant negative response. The

unimodal response of flowering to irradiance is in contrast to many other published

studies, and highlights the potentially damaging effects of high irradiance, and the

importance of making assessments of the effects of environmental factors over a

wide range of levels.

Langton et al. (2003) compared short-day (SD) and long-day (LD) photoperiodic

treatments at equal light integral, for their effects on the seedling growth of four

bedding plant species: geranium, impatiens, pansy and petunia. Total leaf area was

frequently increased by LD given either by day-extension lighting or night-break

lighting, but this response was inconsistent and varied greatly between species and

experiments. In contrast, leaf greenness measured using a SPAD-502 meter, a

measure of chlorophyll content per unit area of leaf, was consistently and

significantly increased in LD in all four species. However, night-break lighting

may have been somewhat less effective than day-extension lighting. Increasing the

day-extension lighting from 16 h to 24 h gave no further intensification of

greenness. Consistent with increases in leaf greenness, total dry weight was

generally increased in LD, and increases were of a similar magnitude to those

given by doubling the daily light integral. The promotional effect of LD on

chlorophyll content appears to have been largely ignored or overlooked in recent

years, but this may be because simple methods for measuring `greenness' have

only recently become widely available.

Warner and Erwin (2003) studied the effect of daily light integral (DLI) (400–

700 nm) and photoperiod on Hibiscus sp. growth and flowering. Hibiscus

coccineus (Medic.) Walt., Hibiscus cisplatinus St-Hil., Hibiscus moscheutos L.

‘Disco Belle Pink’, Hibiscus radiatus Cav., and Hibiscus trionum L. plants were

grown under a 9 h (0730–1630 h) or 16 h (0600–2200 h) photoperiod in a

greenhouse under ambient daylight plus supplemental high-pressure sodium

lighting at 20±1 °C. Within each photoperiod plants were grown under four levels

of supplemental irradiance to achieve four DLIs. Under the 9 h photoperiod, plants

received an additional 0, 2, 4, or 8 mol m−2 per day. Under the 16 h photoperiod,

plants received an additional 2, 4, 8, or 16 mol m−2 per day. Increasing DLI from

8.3 to 25.5 mol m−2 per day (ambient plus supplemental) decreased H. cisplatinus

leaf number below the first flower from 26 to 18 leaves, regardless of photoperiod.

DLI interacted with photoperiod to affect flowering of H. moscheutos and H.

trionum. H. moscheutos leaf number below the first flower was 15±2 leaves under

a 16 h photoperiod, regardless of DLI. Increasing DLI from 12.2 to 20.2 mol m−2

per day reduced H. moscheutos ‘Disco Belle Pink’ leaf number below the first

flower from 24 to 18 leaves, under a 9 h photoperiod only. Increasing DLI did not

affect H. trionum leaf number below the first flower bud initiated, but reduced leaf

number below the first flower to open on plants grown under a 9 h photoperiod. H.

radiatus flowered only under a 9 h photoperiod and leaf number below the first

flower was not affected by DLI. Increasing DLI from 6.7 to 8.9 mol m−2 per day

increased H. radiatus total flower bud number at first flower opening from 7±1 to

10±1 buds, but did not affect flower bud number of the other species. H. coccineus

did not flower during the experiment.

Wiśniewska and Treder (2003) reported that Rosa hybrida ‘Frisco’ and ‘Madelon’

plants were grown during winter in natural light (NL) and two supplementary

lighting time regimes: NL + 6 hours, NL+12 hours per day (PAR 90-110 μmol m-²

s‾¹, depending on the height of the plants). The additional lighting started from 15th

September and it was continued until 30th of March during 4 years of culture. The

roses were grown in the prepared soil in double row. Flowers were collected all

year around, and cut 80–90 cm above the soil level. The analyses of the

carbohydrates were performed on the first five leaflet leaves below the bud and

flower peduncle. The supplementary lighting had the significant effect on the

flowers number of both tested cultivars during the winter periods. The harvested

stems were longer and their number was higher in 12 hours additional light

compared with the natural and 6 hours light (‘Frisco’). The cv. ‘Madelon’ showed

lower demand to supplementary light; its productivity was the same for 6 or 12

hours of additional light. The total carbohydrates content in dry weight in the

leaves was smaller than in peduncles. The amount of glucose fructose and sucrose

in the leaves of ‘Madelon’ was significantly higher than in ‘Frisco’, whereas, they

were higher in peduncles of cv. ’Frisco’ in natural light than with the

supplementary one. The status of the tested fructose, sucrose, glucose and starch is

discussed.

Munir et al. (2004) studied shades of different light intensities (29%, 43%, 54%,

60% or 68%) along with control (no shade) to observe their effects on the

flowering time and plant quality. A hyperbolic relationship was observed between

different light intensities under shade, and time to flowering. The total number of

flower buds showed a curvilinear relationship with light intensities. Growth

parameters related to the plant characteristics such as plant height, leaf area and

plant fresh weight were improved under shading treatments at the expense of

flowering time and number of flower buds. However, both linear and polynomial

models applied assumed that cultivar Chimes White was equally sensitive to light

intensity throughout development.

Souza et al. (2004) assessed the effects of irradiance on non-structural

carbohydrate contents and composition, as well as on the hypoglycemiant activity

of Rhynchelytrum repens, a pantropical grass species popularly used for diabetes

treatment. Plants of R. repens growing under natural irradiance (NI) showed

increased content of total soluble carbohydrate (TSC), higher fluctuations in starch

content (SC) and higher number of tillers. The flowering process of these plants

was preceded by an increase in sucrose. However, their water content was low

when compared to that of plants cultivated under low irradiance (LI). The ratio

root/aerial organs and SC showed no significant differences in plants grown under

LI, although TSC increased and a lower number of tillers were observed during the

experimental period. In both conditions, sucrose was the ubiquitous sugar and

seemed to be involved in the flowering process. A reduction in the blood sugar

level was observed through the intra-peritoneal (IP) administration of the

precipitate of aqueous extracts obtained from plants growing in both conditions of

light; the supernatant fraction showed no hypoglycemic effect.

Wagstaffe and Battey (2004) evaluated growth patterns and cropping over the

season for the everbearing strawberry Éverest` at a range of temperatures (15-

27°C) in two light environments (ambient and 50% shade). The highest yield was

recorded for unshaded plants grown at 23°C, but the optimum temperature for

vegetative growth was 15°C. With increasing temperature fruit number increased,

but fruit weight decreased. Fruit weight was also significantly reduced by shade,

and although Éverest` showed a degree of shade tolerance in vegetative growth,

yield was consistently reduced by shade. Shade also reduced the number of crowns

developed by the plants over the course of the season, emphasising that crown

number was ultimately the limiting factor for yield potential. We conclude that, in

contrast to June-bearers which partition more assimilates to fruit at temperatures

around 15°C optimised cropping in the everbearer Éverest` is achieved at the

significantly higher temperature of 23°C. These findings have significance for

commercial production, in which protection tends to reduce light levels but

increase average temperature throughout the season.

Yeh and Hsu (2004) studied the effects of irradiance on growth and net

photosynthesis in four cultivars of Hedera helix L. grown in controlled

environments at a mean daily temperature of 24°C. Shoot dry weights of the

variegated cultivars Ingelise and Mini Adam were greatest at around 2.9 MJ m-2 d-

1. For the two green cultivars, with increasing daily light integral from 1.2 to 7.2

MJ m-2 d-1, shoot dry weight increased in ´Dark Pittsburg`, but decreased in

Évergreen`. Shoot or internode lengths, and leaf area decreased linearly while leaf

thickness increased as light integral increased from 1.7 to 7.2 MJ m-2 d-1 in

cultivars Ingelise, Dark Pittsburg and Evergreen. Leaf variegation increased in

Íngelise` under 4.3 or 7.2 MJ m-2 d-1, while leaf variegation in ´Mini Adam` was

affected little by irradiance. Plants of ´Dark Pittsburg` had both higher

lightsaturated net photosynthesis rate and light saturation point than other cultivars.

The variegated cultivars Ingelise and Mini Adam had higher light compensation

points than the green cultivars Dark Pittsburg and Evergreen.

Adams and Langton (2005) reported that long-day (LD) treatments frequently

promote an increase in dry weight in plants that otherwise grow in short days (SD).

Responses can be substantial. Increases for grass species have averaged around 52

percent;. However, LD treatments (day extension, night-break, etc) frequently vary

in their effectiveness. A direct promotional effect of LD treatment on leaf

expansion and total photosynthetic area provides one possible mechanism. Of 50

species surveyed, 41 (82 percent) gave larger or longer leaves in LD, six (12

percent) gave larger or longer leaves in SD, and three (6 percent) showed no leaf

extension response. Increase in leaf area is frequently accompanied by an increase

in specific leaf area (SLA) and, in such cases, it is clear that an increase in leaf area

occurs ahead of an increase in dry weight. Increased SLA is frequently associated

with reduced net assimilation rate (NAR), but this is generally more than

compensated for by greater leaf area. In other cases, increase in leaf area in LD

treatment is not accompanied by increased SLA. In such cases, dry weight gain

may itself be driving leaf area expansion, possibly mediated by an influence of LD

on assimilate partitioning. Increases in leaf size are associated with increases in

both cell size and cell number, and a photoperiodic growth stimulus has been

shown to be transmissible from mature leaves to developing leaves. Gibberellins

may be implicated, but responses to exogenous gibberellins and LD treatment are

rarely exactly the same. Parallels are noted between LD treated leaves and low-

irradiance, 'shade' leaves, suggesting that, in some cases, this may be because

plants respond to the average irradiance over the lit period. Chlorophyll per unit

leaf area is occasionally increased by LD treatment, which may increase

photosynthesis and constitute a second mechanism that increases dry weight.

Furthermore, lighting at a lower irradiance over a longer period may be more

efficient than a high irradiance SD treatment due to the hyperbolic relationship

between PAR and photosynthesis. Low intensity LD lighting can, at least in part,

offset respiration. The LD growth phenomenon has yet to be exploited in

commercial crop production, but the potential benefits are clear.

Fausey et al. (2005) evaluated the growth and development of Achillea ×

millefolium L. 'Red Velvet', Gaura lindheimeri Engelm. and Gray 'Siskiyou Pink'

and Lavandula angustifolia Mill. 'Hidcote Blue' under average daily light integrals

(DLIs) of 5 to 20 mol m-2 d-1. Plants were grown in a 22 ± 2°C glass greenhouse

with a 16-h photoperiod under four light environments: 50% shading of ambient

light plus PPF of 100 μmol.m-2 s-1 (L1); ambient light plus PPF of 20 μmol m-2 s-1

(L2); ambient light plus PPF of 100 μmol m-2 s-1 (L3); and ambient light plus PPF

of 150 μmol m-2 s-1 (L4). Between 5 to 20 mol m-2 d-1, DLI did not limit flowering

and had little effect on timing in these studies. Hence, the minimum DLI required

for flowering of Achillea, Gaura and Lavandula must be <5 mol m-2 d-1, the lowest

light level tested. However, all species exhibited prostrate growth with weakened

stems when grown at a DLI of about 10 mol m-2 d-1. Visual quality and shoot dry

mass of Achillea, Gaura and Lavandula linearly increased as DLI increased from 5

to 20 mol m-2 d-1 and there was no evidence that these responses to light were

beginning to decline. While 10 mol m-2 d-1 has been suggested as an adequate DLI,

these results suggest that 15 to 20 mol m-2 d-1 should be considered a minimum for

production of these herbaceous perennials when grown at about 22°C.

Faust et al. (2005) quantified the growth and flowering responses of bedding plants

to DLI. Eight bedding plant species, i.e. ageratum (Ageratum houstonianum cv.

Hawaii White), begonia (Begonia semperflorens-cultorum cv. Vodka Cocktail),

impatiens (Impatiens walleriana cv. Cajun Red), marigold (Tagetes erecta cv.

American Antigua Orange), petunia (Petunia hybrida cv. Apple Blossom), salvia

(Salvia coccinea cv. Lady in Red), vinca (Catharanthus roseus cv. Pacific Lilac)

and zinnia (Zinnia elegans cv. Dreamland Rose), were grown outdoors in direct

solar radiation or under one of three shade cloths (50, 70 or 90% photosynthetic

photon flux (PPF) reduction) that provided DLI treatments ranging from 5 to 43

mol m-2 day-1. The total plant dry mass increased for all species, except begonia

and impatiens, as DLI increased from 5 to 43 mol m-2 day-1. The total plant dry

mass of begonia and impatiens increased as the DLI increased from 5 to 19 mol m-

2 day-1. Impatiens, begonia, salvia, ageratum, petunia, vinca, zinnia and marigold

achieved 50% of their maximum flower dry mass at 7, 8, 12, 14, 19, 20, 22 and 23

mol m-2 day-1, respectively. The highest number of flowers for petunia, salvia,

vinca and zinnia was obtained at 43 mol m-2 day-1. The time to flowering decreased

for all species, except begonia and impatiens, as the DLI increased to 19 or 43 mol

m-2 day-1. There was no consistent plant height response to DLI across species,

although the shoot and flower dry mass per unit height increased for all species as

the DLI increased from 5 to 43 mol m-2 day-1. Guidelines for managing DLI for

bedding plant production in greenhouses are discussed.

Kubota et al. (2005) investigated the effects of light intensity and temperature on

growth, flowering, and single-leaf CO2 assimilation of Odontioda orchid. CO2

assimilation in final leaves of back and current shoots was depressed significantly

at a leaf temperature of about 30°C, in association with decreased stomatal

conductance, although the light saturation point differed somewhat between back

shoots and current shoots. A photosynthetic photon flux density (PPFD) of about

400 μmol m-2 s-1 was optimum for CO2 assimilation. Large quantities of sugar and

starch were reserved in pseudobulbs of back shoots under high light intensity, but

they contents decreased while the current shoot was developing new leaves. When

growth stopped, the amount of reserve assimilates increased again. Thus, there

appears to be a dynamic translocation of assimilates between the pseudobulbs of

back shoots and current shoots. All plants cultivated under a 28/18°C (day/night)

died within 2 months after the beginning of the experiment confirmed that this

species has low heat tolerance. Growth and flowering were stimulated at 23/13°C

and a PPFD ranging between 300 and 500 μmol m-2 s-1. These conditions seem to

approximate the optimum conditions for CO2 assimilation.

Mattson and Erwin (2005) studied forty one herbaceous species under short-days

(8 h photoperiod, ambient irradiance averaged 12–13.2 and 6.4–8.3 mol m−2 day−1

for Experiments I and II, respectively) with or without supplemental high-pressure

sodium lighting (+50, 100, or 150 μmol m−2 s−1); or under long-days delivered

using natural day lengths and irradiance with night interruption lighting (2200–

0200 h at 2 μmol m−2 s−1 from incandescent lamps) or under ambient daylight plus

supplemental irradiance during the day and as a day extension to 18 h (0800–

0200 h) with supplemental high pressure sodium lighting (+50, 100, or

150 μmol m−2 s−1) to identify the impact of photoperiod and irradiance on

flowering of each species. Days to first open flower, leaf number below first

flower, and mean dry weight gain per day (MDWG) were measured when the first

flower opened. Twenty-seven species were photoperiodic with examples of five

photoperiodic response groups represented: obligate short-day (2), facultative

short-day (5), obligate long-day (16), facultative long-day (4); 13 were day neutral

(no photoperiod response in flowering). One species, Salvia sclarea L., did not

flower. A facultative irradiance response was observed with 10 species; 28 species

were irradiance indifferent; 2 had delayed flowering as irradiance increased.

Photoperiod affected MDWG of 30 species. Increasing irradiance affected MDWG

with 14 species. Photoperiod interacted with irradiance to affect MDWG of 11

species. Cobaea scandens had the greatest MDWG (0.40 g day−1) while

Amaranthus hybridus had the least MDWG (0.01 g day−1) across photoperiod and

irradiance levels.

Tañase et al. (2005) placed potted Delphinium hybrid 'Bcllamosum' plants under a

photosynthetic photon flux density (PPFD) of 7, 70 and 300 μmol.m-2.s-1, their

flower life, which terminated when sepal abscission occurred, was 6.4, 9.4 and 9.4

days, respectively. The capacity for CO2 assimilation on day 0 was negative at 7

μmol.m-2.s-1. Four days after the onset of the light treatment, the concentrations of

sucrose, glucose, fructose, and mannitol in sepals and gynoecia were positively

correlated with light intensity. Flowers held at 7 μmol.m-2.s-1 had a higher ethylene

production on day 6, compared with flowers held at higher light intensity. The low

light intensity that resulted in increased ethylene production may be attributed to

the preceding reduction of CO2 assimilation and sugar content, which, in turn led

to the acceleration of sepal abscission.

Wang et al. (2005) studied the effects of low light intensity on sucrose synthase,

the key enzyme in sucrose metabolism in nectarine (Prunus persica L. var.

nectarina) grown in a greenhouse. Experiments were conducted under two light

regimes: a photosynthetic photon flux (PPF) of 588 ± 0.32 µmol m-2 s-1 (full sun)

and a PPF of 150 ± 1 µmol m m-2 s-1 (low light). Concentrations of sucrose were

lower under low light [1.47 ± 0.2 mg g-1 fresh weight (FW)] than in full sun (1.56

± 0.4 mg g-1 FW), whereas there was no effect on the concentrations of glucose

and fructose. The activity of sucrose synthase (SS) was also lower under shade

(0.15 ± 0.05 nmol min-1 g-1 FW) than in full sun (0.26 ± 0.05 nmol min-1 g-1 FW).

An 87 kDa polypeptide was detected by western blotting using antiserum specific

for SS, and was present at similar levels in low light and in full sun. Electron

microscopy and immunogold-labelling showed that SS was localised mainly in the

vacuole rather than in the cytoplasm of phloem parenchyma (PP) cells and in

nacreous cell walls (NCW). However, SS activity decreased in low light,

suggesting that low light reduced the specific activity but not the amount of SS in

nectarine leaves. As sucrose production in nectarine leaves is affected primarily by

the activity of SS, to improve the quality of greenhouse-grown nectarines,

additional light should be provided.

Warner and Erwin (2005) examined the impacts of temperature and irradiance on

herbaceous ornamental flowering and to select a model to study high temperature-

reduced flowering, Antirrhinum majus L. (Snapdragon) 'Rocket Rose', Calendula

officinalis L. (calendula) 'Calypso Orange', Impatiens wallerana Hook.f.

(Impatiens) 'Super Elfin White', Mimulus × hybridus Hort. ex Siebert & Voss

(Mimulus) 'Mystic Yellow', and Torenia fournieri Linden ex E. Fourn (Torenia)

'Clown Burgundy' were grown at constant 32±1°C or 20±1.5°C under a 16-hour

photoperiod with daily light integrals (DLI) of 10.5, 17.5, or 21.8 mol m-2 d-1.

Flower bud number per plant (all flower buds ≥1 mm in length when the first

flower opened) of all species was lower at 32 than 20°C. Reduction in flower bud

number per plant at 32 compared to 20°C varied from 30% (Impatiens) to 95%

(Torenia) under a DLI of 10.5 mol m-2 d-1. Flower diameter of all species except

Snapdragon was less at 32 than 20°C. Decreasing DLI from 21.8 to 10.5 mol m-2 d-

1 decreased flower diameter of all species except Snapdragon. Calendula,

Impatiens, and Torenia leaf number below the first flower was greater at 32 than

20°C, regardless of DLI. Increasing DLI from 10.5 to 17.5 mol m-2 d-1 increased

shoot dry mass gain rate of all species, regardless of temperature. Further

increasing DLI from 17.5 to 21.8 mol m-2 d-1 at 20°C increased shoot dry mass gain

rate of all species except Snapdragon and Mimulus, indicating that these species

may be light saturated below 21.8 mol m-2 d-1. Under DLIs of 17.5 and 21.8 mol m-

2 d-1 shoot dry mass gain rate was lower at 32 than 20°C for all species except

Torenia. Torenia shoot dry mass gain rate was 129 mg.d-1 at 20°C compared to 252

mg d-1 at 32°C under a DLI of 17.5 mol m-2 d-1. We suggest Torenia may be a good

model to study the basis for inhibition of flowering under high temperatures as

flowering, but not dry mass gain, was reduced at 32°C.

King (2006) reported that plant function, architecture and reproduction are affected

in major ways when plants are grown in protected cultivation or in artificial

lighting. Removal of UV-B by glass has significant effects and reduced visible

light transmission may limit photosynthesis and delay flowering. The converse,

enhanced flowering in higher light intensities is associated with growth but also

with a specific florigenic effect of increasing shoot apex sucrose content. One

outcome is that synchronized flower induction is possible by growing plants at a

limiting light intensity then shifting them to higher intensity. Controlled shading in

commercial production systems could achieve this result but using artificial

lighting to boost flowering would be inefficient. On the other hand, for long day

(LD) responsive species, flowering can also be induced by overnight exposures to

a low irradiance from incandescent lamps while short day (SD) responsive species

can be kept vegetative in such LD. While effective for flowering, such far-red

(FR)-rich light also increases stem/petiole elongation, probably because of

increases in the content of the gibberellin (GA) class of plant hormones. The

flowering and elongation of Arabidopsis thaliana in response to LD provides an

ideal system for the study of the action of FR light on GA synthesis and,

particularly, because extensive molecular and genetic information is available for

this species. Its petiole elongation almost doubles in FR-rich light compared to red

(R) whether given as a 10 min end-of-day (EOD) FR exposure or as a LD (16 h

light). That brief and prolonged low intensity FR exposures are effective shows

that photosynthesis is not limiting. More cogently, genetic evidence using a phyA

mutant along with studies of R/FR photoreversibility affirms a role for the “B”

class of phytochromes. Applied GA mimics the effect of a LD extended by FR

both by increasing petiole elongation and by causing flowering in SD.

Furthermore, after a LD the endogenous content of GAs in growing petioles can

increase 3-fold and, within 4 h of starting the LD, expression of an important

biosynthetic gene, a GA 20-oxidase, has increased 5- to 10-fold. Conversely, in a

20-oxidase gene-silencing line the flowering response to LD is reduced

considerably. Similar findings on GA biosynthesis have been obtained for the grass

Lolium temulentum where LD leads to increases in both 20-oxidase expression and

in leaf GA5 content. The timing of the GA5 increase at the shoot apex is delayed

relative to that in the leaf but this fits with the expected speed and distance of its

transport. Thus, GA5 may be a floral signal transmitted from the leaf to the apex.

Overall, these findings highlight important responses of both growth and flowering

to light intensity and spectral quality. While the findings on the regulation of GA

biosynthesis cannot be applied directly to commercial enterprises, the

understanding of GA metabolism provides a focus for future manipulation of plant

growth.

Waaseth et al. (2006) reported that the transition to flowering in the herbaceous

ornamental perennial Salvia × superba Stapf ‘Blaukönigin’ is promoted by

increasing the photosynthetic photon flux (PPF), in addition to a facultative

response to both vernalization and long photoperiods. Floral evocation occurred at

an earlier developmental stage in unvernalized S. superba in response to increasing

the PPF from 50 to 200 µmol m-2 s-1 irrespective of photoperiod, although the

response was more prominent in 20-hour days compared with short days of 10

hours. After a saturating vernalization treatment, the response to PPF was bypassed

when plants were grown in long photoperiods. The promotion of flowering by

increasing light quantity seems to be dependent on the ambient light level during

the actual evocation process irrespective of the light level received during previous

vegetative growth. Further investigations are needed to uncover the response

mechanism behind this PPF dependent flowering pathway.

Moharekar et al. (2007) reported that Arabidopsis thaliana L., ch1-1 (chlorophyll

b-less mutant), gi-1 (GI deficient mutant), cry2-1 (blue-light-photoreceptor CRY2

deficient mutant), and Columbia (Col; wild ecotype) were grown under broad

range of irradiances (I) from the beginning of germination and the effect of I on the

survival, development, and flowering was studied. Under low and moderate I

(<300 µmol m−2 s−1), flowering time and plant size at flowering showed great

variations among ch1-1, gi-1, cry2-1, and Col, whereas under higher I (>500 µmol

m−2 s−1), these characteristics were almost the same. Hence under high I,

development and flowering of ch1-1, gi-1, cry2-1, and Col converged to almost the

same state. Flowering time was negatively correlated with I, and under high I

acclimation in A. thaliana was associated with a decrease in chlorophyll (Chl)

content and increases in xanthophyll cycle pool and membrane-bound APX

activity (EC 1.11.1.11) suggesting that an increase in oxidative stress induces

earlier flowering. The plants of gi-1 and cry2-1 survived but Col and ch1-1 died

under 1 000 µmol m−2 s−1, showing that mutants deficient in GI or CRY2 are more

photo-stress-tolerant than Col and the Chl b-less mutant. Hence high I promotes in

plants of Arabidopsis raised from germination till flowering the development and

flowering time involving modulation of the photosynthetic apparatus, and this

promoting effect is independent of the functions of flower-inducing GI or CRY2

gene. This can be regarded as photo-acclimation of A. thaliana for survival and

reproduction under high I.

Walton et al. (2007) studied the reduced R/FR ratio- and low PAR-mediated

effects of shade on flowering in the ramets of Stellaria longipes Goldie s.l.

(Caryophyllaceae) ecotypes collected from alpine “sun” and lower elevation prairie

“shade” habitats. Both ecotypes were also tested for their flowering response

(defined as the number of open flowers per ramet) to daylength. The alpine

ecotype plants can best be classified as day-neutral, whereas prairie ecotype plants

require long-days (LD). Under a low PAR of 115μmol m-2·s-1 given under LD

conditions at a reduced (0.7) R/FR ratio, alpine ecotype plants flowered

significantly later relative to plants grown under the low PAR at a normal (1.22)

R/FR ratio. In contrast, plants of the prairie ecotype flowered earlier under the

reduced R/FR ratio combined with the same low PAR. Flower number per ramet

differed significantly between the two ecotypes, with alpine ecotype plants

developing fewer flowers under a low PAR (109μmol m-2·s-1 irradiance) relative to

a high PAR of 611μmol m-2·s-1 (both given at a normal R/FR ratio). The prairie

ecotype plants responded differently and had similar flower numbers under both

low and high PARs at the normal (1.22) R/FR ratio. However, growing the prairie

ecotype plants under a reduced R/FR ratio at a low PAR showed a significant

increase in number of flowers. In contrast, plants grown under high (2.7) and

normal (1.9) R/FR ratios combined with low PAR produced many more flowers

than the alpine ecotype. Thus, the two components of shade, reduced R/FR ratio

and low PAR can cause distinctly different flowering responses in sun and shade

plants of S. longipes.

Woźny and Jerzy (2007) established four narcissus cultivars under artificial light

using fluorescent lamps, which emitted white (307-770 nm), blue (393-580 nm),

red (540-760 nm), yellow (450-750 nm), or green (387-680 nm) light. The

photosynthetic photon flux density was 12.5μmol m-2 s-1, with a 6 h photoperiod.

Light colour (wavelength) had no significant effect on flowering date, or on the

number of flowers collected (P < 0.05). Narcissus bulbs exposed to blue light

(393-580 nm) formed shorter, more rigid shoots of lower weight with 13–40%

shorter leaves.

Adams et al. (2008) examined the responses of Petunia, Impatiens, and tomato to

LD lighting treatments and concludes that no single mechanism can explain the

growth promotion observed in each case. Petunia showed the most dramatic

response to photoperiod; up to a doubling in dry weight (DW) as a result of

increasing daylength from 8 h d-1 to 16 h d-1. This could be explained by an

increase in specific leaf area (SLA) comparable to that seen with shading. At low

photosynthetic photon flux densities (PPFD), the increased leaf area more than

compensated for any loss in photosynthetic capacity per unit leaf area. In Petunia,

the response may, in part, have also been due to changes in growth habit. Impatiens

and tomato showed less dramatic increases in DW as a result of LD lighting, but

no consistent effects on SLA or growth habit were observed. In tomato, increased

growth was accompanied by increased chlorophyll content, but this had no

significant effect on photosynthesis. In both species, increased growth may have

been due to a direct effect of LD lighting on photosynthesis. This is contrary to the

generally held view that light of approx. 3-4 μmol m-2 s-1 is unlikely to have any

significant impact on net photosynthesis. Nevertheless, we show that the

relationship between PPFD and net photosynthesis is non-linear at low light levels,

and therefore low intensity LD lighting can offset respiration very efficiently.

Furthermore, a small increase in photosynthesis will have a greater impact when

ambient light levels are low.

Cummings et al. (2008) reported that pea (Pisum sativum L.) plants were grown

under no shade, 50% neutral shadecloth, or 50% blue, or 50% red photoselective

shadecloths. Under the red and blue shadecloths, the blue fraction was altered, but

there was little alteration in other wavelengths relative to neutral shadecloth or to

sunlight. Relative to neutral shadecloth, shoot length was reduced significantly

under blue shadecloth, and increased significantly under red shadecloth. The effect

of the red and blue shadecloths appeared to be mediated by alterations in blue

irradiance perceived by the blue light cry1 photoreceptor, as, unlike wild-type

(WT) peas, cry1 mutant peas did not respond to the shadecloth treatments. Levels

of GA1 were reduced under blue shadecloth in WT pea plants compared with

neutral shadecloth, but not in cry1 mutant plants. This study demonstrates that

photoselective shadecloths can be used to manipulate plant height and flowering in

crops with a strong response to blue irradiance.

Lopez and Runkle (2008) quantified how the mean DLI influenced rooting and

subsequent growth and development of two popular vegetatively propagated

species, New Guinea impatiens (Impatiens hawkeri Bull.) and petunia (Petunia

∙hybrida Hort. Vilm.-Andr.). Three cultivars of each species were propagated

under a mean DLI ranging from 1.2 to 10.7 mol m–2 d–1. Cuttings were rooted in a

controlled greenhouse environment maintained at 24 to 25 ºC with overhead mist,

a vapor-pressure deficit of 0.3 kPa, and a 12h photoperiod. Rooting and growth

evaluations of cuttings were made after 8 to 16 d. In a separate experiment, rooted

cuttings under DLI treatments were then transplanted into 10 cm containers and

grown in a common greenhouse at 21±2 8C under a 16h photoperiod to identify

any residual effects on subsequent growth and development. In both species,

rooting, biomass accumulation, and quality of cuttings increased and subsequent

time to flower generally decreased as mean propagation DLI increased. For

example, root number of petunia ‘Tiny Tunia Violet Ice’ after 16 days of

propagation increased from 17 to 40 as the propagation DLI increased from 1.2 to

7.5 mol m–2 d–1. In addition, cutting shoot height decreased from 6.3 to 4.5 cm, and

root and shoot dry biomass of cuttings harvested after 16 days of propagation

increased by 737% and 106%, respectively. Subsequent time to flower for ‘Tiny

Tunia Violet Ice’ from the beginning of propagation decreased from 50 to 29 days

as propagation DLI increased from 1.4 to 10.7 mol m–2 d–1 regardless of the DLI

provided after propagation. In New Guinea impatiens ‘Harmony White’, root and

shoot dry weight of cuttings increased by 1038% and 82%, respectively, and

subsequent time to flower decreased from 85 to 70 days as the propagation DLI

increased from 1.2 to 10.7 mol m–2 d–1. These experiments quantify the role of the

photosynthetic DLI during propagation on the rooting and subsequent growth and

development of vegetatively propagated herbaceous ornamental cuttings.

Haliapas et al. (2008) reported that Petunia × hybrida was grown under high (H),

medium (M) and low (L) light intensity [photoperiod; 16 h d−1, photosynthetic

photon flux density (PPFD); 360, 120 and 40 μmol m−2 s−1, respectively] as well as

under end-of-day (EOD) red (R) and far-red (FR) light quality treatments

[photoperiod; 14.5 h d−1, PPFD; 30 μmol m−2 s−1 EOD; 15 min, Control (C) light;

without EOD light treatment]. Shoot growth, leaf anatomical and photosynthetic

responses as well as the responses of peroxidase (POD) isoforms and their specific

activities following transition to flowering (1-6 weeks) were evaluated. Flower bud

formation of Petunia × hybrida was achieved at the end of the 4th week for H light

treatment and on the end of the 6th week for FR light treatment. No flower bud

formation was noticed in the C and R light treatments. H and M light treatments

induced lower chlorophyll (Chla, Chlb, Chla+b) concentrations in comparison to L

light. On the other hand R and FR light chlorophyll content were similar to C light.

Photosynthetic parameters [CO2 assimilation rate (A), transpiration rate (E) and

stomatal conductance (gs) values] were higher in the H light treated plants in

comparison to M and L light treated plants. A, E and gs values of R and FR light

were similar to C light plants. Leaf anatomy revealed that total leaf thickness,

thickness of the contained tissues (epidermis, palisade and spongy parenchyma)

and relative volume percentages of the leaf histological components were

differently affected within the light intensity and the light quality treatments. POD

specific activities increased from the 1st to the 6th week during transition to

flowering. Native-PAGE analysis revealed the appearance of four anionic POD

(A1–A4) isoforms in all light treatments. On the basis of the leaf anatomical,

photosynthetic and plant morphological responses, the production of high quality

Petunia × hybrida plants with optimal flowering times could be achieved through

the control of both light intensity and light quality. The appearance of A1 and A2

anionic POD isoforms could be also used for successful scheduling under light

treatments.

Levi et al. (2008) examined the effect of shading ornamental pot plants with a

pearl-coloured polyethylene net that increased the percentage of scattered light

more than five-fold compared to a neutral black shade net, without changing the

light spectrum. The two plants chosen for this study were Myrtus communis and

Crowea 'Poorinda Extasy'. The increase in scattered light due to shading with the

pearl net had a dramatic effect on both plants: M. communis plants grew in a more

compact form, with a larger number of branches; while, in Crowea 'Poorinda

Extasy' plants, there was a significant increase in the number of flowers per plant.

Crowea 'Poorinda Extasy' plants flowered throughout the year and did not seem to

be dependent on a specific temperature or day-length. However, the number of

flowers per plant was highest under elevated temperatures (26°/18°C; day/night,

respectively) and under a short-day regime of 10 h. This report proposes an

alternative, environmentally friendly and non-labour intensive method for shaping

ornamental pot plants by manipulation of the light reaching the plants.

Oh et al. (2008) performed experiments to examine the effect of DLI using two

temperatures (16°C or 20°C) and three photoperiods (8, 12, or 16 h) delivering

DLI values of 4.9, 7.3, or 9.8 mol m-2 d-1, respectively, and the effect of night

interruption (NI) lighting from incandescent lamps (IL), on the flowering of

cyclamen ‘Metis Purple Flame’. Plants grown at 20°C reached the visible flower

bud (VB) stage earlier than plants grown at 16°C under all photoperiods. NI

hastened flower bud initiation by 22-29 d compared with an 8-h photoperiod at

both temperatures. Plants grown under the 8-h photoperiod with an NI treatment

(DLI = 4.9 mol m-2 d-1) flowered at a similar time as plants grown under the 12-h

photoperiod (DLI = 7.3 mol m-2 d-1). In addition, plants grown at 16°C with an NI

reached the VB stage in a similar time to plants grown at 20°C with an 8-h

photoperiod. Therefore, the effects of increasing the DLI, providing NI lighting, or

increasing the temperature can be compared, so that growers can determine which

strategies can reduce the greenhouse production time of cyclamen most cost-

effectively.

2.2 Photoperiod

Tsukamoto et al. (1968) investigated the flowering response of marigolds to the

photoperiod using one cultivar of African, four cultivars of French and one cultivar

of Signet marigolds. Marigold is a quantitative short day plant, but this

photoperiodic nature varies depending on the strain or cultivar. African marigold

(Tagetes erecta) shows the weakest, French (T. patula) the intermediate, and

Signet (T. tenuifolia) the strongest requirement for short photoperiod, although

there are some differences in the requirement among cultivars of the French

marigold. Marigold can initiate floral primordia under both short and long day

conditions, but the long day condition retards the development of flower buds. No

retardation was noted in flower initiation in African or French marigold regardless

of day-length, but there was a slight retardation of flower initiation in Signet

marigold in long photoperiod.

Tsukamoto et al. (1971) reported that French marigold, cultivar Butter Ball

produced no flowers under long day (continuous illumination or 18 hours)

conditions at 30°C, but did produce a high percentage of flowering under short day

(10h) conditions at the same temperature. However, there was a slight difference in

the flowering percentages between the long day and the short day lots at 20°C.

Combinations of day length and temperature caused no marked differences in

flowering of African marigold. Under conditions where the light intensity was

reduced to below about 50% of full sunlight, anthesis did not occur in the long day

(16h) lot, while normal flowers developed in the short day (10h) lot. Naturally, the

more the light was reduced the fewer flowers were produced. Gibberellic acid

slightly enhanced flowering of French marigold, while TIBA had no influence.

Gentner et al. (1975) reported that opium poppy, Papaver somniferum L., is a

long-day plant with a critical daylength for flowering of 14 to 16 hours. Flowering

is induced by two or more long photoperiods or by a single period of light longer

than 24 hours. Flowering stems always lengthen, but stems also sometimes

lengthen in the absence of flowering, e.g. with the application of gibberellic acid.

Flowering was not controlled by brief red, far-red irradiations or both. Thus, the

action of phytochrome was not shown, but its presence was not excluded. Light

seems to control poppy flowering through a so-called high-energy reaction.

Yanagisawa (1975) studied flax plants to natural long day (14hrs 20 min to 14hrs

40 min) after having received 2 (SCi), 3 (SC2) and 4 weeks (SCs) of the short day

(8hrs). The short day (S) and natural long day (C) plots were provided as controls.

When short day was followed by long day, the flax plants grew rapidly and their

stems, elongated more than those of the C plot on the later growth stage. The

dicotyledonal axilla of the plants transferred from S to C in the earlier growth stage

grew longer than those of the S plot. The longer period of the short day treatment,

the longer branches were produced. These results may be attributable to the effects

of short day. 2) The dry weight of the above-ground parts of the flax plant, when

transferred from S to C, reduced in comparison with that of the C plot. This seems

to ascribe to the effect of short day, because of the rapid elongation of the plants.

3) When the flax plants were transferred from S to C, the effect of short day was

recognized in the date of anthesis. Date of anthesis in the SC3 plot delayed only a

little compared.

Okusanya (1980) reported that continuous light or alternating light and dark appear

to be necessary for good germination of Celosia cristata L. As temperature

increased up to 31°C so did germination; thereafter, it decreased. There appears to

be a preference for high constant or high alternating temperatures in germination.

As light intensity decreased so did growth in terms of leaf area, dry weight and

relative growth rate. Proportionally more leaf is also made and leaf:area ratio

increased. However, root weight ratio decreased. Although both high light intensity

and high temperature are required for the good growth of Celosia, temperature

appeared to be more important than light. A reduction of less than one-third of full

light may not cause a significant reduction in growth. The results explain the

observed differences in the nature of C. cristata in the field as well as its

distributional limits.

Goyne and Hammer (1982) studied the effects of photoperiod and temperature on

the phenology of the open-pollinated sunflower cultivar, Sunfola 68-2, the hybrid,

Hysun 30, and its parents in five experiments using the CSIRO Canberra

phytotron. Photoperiod and temperature influenced the number of days to first

anthesis (FA) mainly during the emergence (E) to head-visible (HV) stage of

growth. Leaf counts and plant height measurements supported this finding. There

were major differences in the responses of the two cultivars to short photoperiods

and low temperatures. The differences were removed by increasing temperature to

a regimen of 27/22ºC (day/night) or by increasing the photoperiod to 14 h. At low

temperature, Sunfola 68-2 showed little response to photoperiods of between 10

and 14 h, whereas Hysun 30 showed a marked increase in duration of the E-HV

stage for photoperiods shorter than 14 h. At photoperiods of 10 and 12 h there was

a general decline in all measured attributes with increases in temperature, except

the number of leaves on Sunfola 68-2 which remained relatively constant. Hysun

30 was similar to its male parent ('R' line) in response to photoperiod and

temperature. The experiments suggest that the effects of radiation levels on

sunflower phenology and photoperiod × temperature interactions in the 14-18 h

photoperiod range require further investigation.

Goyne and Schneiter (1987) determined the influence of photoperiod on

phenological development in a diverse group of sunflower genotypes. An

understanding of this response would allow the development of a model to predict

sunflower anthesis. Sixteen sunflower genotypes, including hybrid and inbred

lines, were classified for photoperiod response in greenhouse plantings carried out

over a 2-yr period at Fargo, ND (latitude 4°54'N, elevation 183 m). Plantings were

made so that emergence occurred each time natural photoperiod changed by about

1 h. Although some genotypes displayed long-day, short-day, or insensitive

photoperiodic reactions for the period from emergence to floral bud development,

many of the genotypes appeared to be ambiphotoperiodic, with 11 through 13 h at

emergence being the photoperiods delaying time to flower bud development. This

delay could be of consequence to breeding programs in those latitudes where

planting dates may result in emergence and early growth of the sunflower

coinciding with these intermediate photoperiods.

Al-hemaid et al. (1990) reported that Petunia `Red Flash', Vinca `Little Blanch',

Pansy `Magestic Giant Purple', and Impatien `Super Elfin Red' plugs were held in

the greenhouse after they reached the saleable size in 200, 406, 512, and 800 for 1

to 3 weeks Pansy plugs were held in coolers at 40, 50, or 60 ºF under fluorescent

light for 16 hrs photoperiod for 1 to 3 weeks in 200, 406, 512, or 800 plug trays.

All plants ware transplanted weekly and were grown in the greenhouse until

flowering and data were collected. For plants bald in the greenhouse, plants were

affected by transplanting time. As the holding time increased the final height,

diameter, flower number, and fresh and dry weight of plants decreased. The

flowering time was delayed by increase the holding time, regardless of plant

variety, as cell size decreased, plant height, diameter, flower number, and fresh and

dry weight decreased. For plants held in the coolers, the flowering time was

delayed by the transplant time, regardless of cooler temperatures Plant quality was

not affected by the treatment. The height, diameter, flowers number, and fresh and

dry weight of plants showed a little effect by temperatures, cell size, and

transplanting time.

Healy and Graper (1990) established Petunia `Red Flash' seedlings were grown

under HPS (175 µmol m-2 s-1) photoperiod treatments of 10, 12, 14 or 16 hr at 20oC

soil temperature in a shaded glasshouse where the maximum peak PPF was reduced

to 150 µmol m-2 s-1. Seedling were transplanted after they had unfolded a specific

number of leaves and grown under natural days or placed under photoperiod

treatments which consisted of an 8 hr natural day with incandescent day extension

treatments of 1 to 6 hours. A 16 hr HPS treatment decreased the days to transplant

(DTT) by more than 4 days and reduced the days from transplant to flower (DTF)

by more than 5 days. The total reduction in days from sowing to flower (DSTF)

was at least 8 days. When compared to unlighted controls, the reduction in DSTF

was 26 days. The longer the seedlings remained under the HPS treatments, the

shorter the DTF and DSTF. Premature shifting of plants to natural days resulted in

up to a 9 day delay in DSTF. At photoperiods greater than 13 hr, the number of

nodes subtending the inflorescence becomes constant regardless of number of

leaves at transplant.

Shibata et al. (1992) investigated the effect of daylength (from 9 to 15 hours) and

cultivation temperature (from about 13 to 25 ºC) on flower bud differentiation of

three strains of Papaver somniferum L. cv. Ikkanshu, which have been cultivated

in Nayoro (Hokkaido), Tsukuba (Central Honshu) and Nagasaki (Kyushu) for the

last a few decades. 1. The experiment on the effect of daylength on flowering

revealed that the longer the photoperiod was, the earlier flowering occurred. 2.

Flower bud differentiation was observed at temperatures of 20 ºC or less but never

at 25 ºC and it was more quickly induced at lower temperatures. Furthermore, we

also found that the optimum temperature for flower bud development following

differentiation was 20 ºC. From these findings, we reached the conclusion that this

species has thermo-sensitivity. 3. Flower bud differentiation clearly occurred later

in the Nayoro strain than in the Nagasaki strain or the Tsukuba strain. This seems

to indicate that the Nayoro strain is a different ecological type from other strains. 4.

When we compared the size and dry weight of the capsules, which are known to be

closely related to opium yield, the capsules of the Nagasaki and Tsukuba strains

were considerably smaller and lighter than those of the Nayoro strain. This is

attributable to the fact that flower bud differentiation occurred at an early stage

before the achievement of sufficient vegetative growth in the Nagasaki and

Tsukuba strains.

Erwin and Schwarze (1993) placed Antirrhinum majus L. cv `Winchester'

seedlings (first true leaf stage) in controlled environment chambers at 20oC under 8,

10, 12 or 14 hr photoperiods for flower induction. Seedlings were grown at

irradiance levels of 240, 315, 380 or 460 µmol s-1 m-2 within each chamber. Plants

were removed after 7, 14 or 21 days and were placed in a glasshouse maintained at

20 ± 2oC under natural photoperiod and irradiance levels for flower development.

Data were collected on flower number and number of nodes below the first flower

when all flowers were visible on the inflorescence. Node number decreased from

67 to 43 nodes as photoperiod increased from 8 to 14 hrs. Increasing irradiance

hastened flowering on plants grown under 8-12 hr photoperiods only and had no

effect on flower number. Flower number increased from 23 to 30 as photoperiod

length increased from 8 to 14 hrs. Node number decreased from 57 to 44 nodes and

flower number increased from 22 to 31 flowers as the time of treatment increased

from 7 to 21 days under the 14 hr photoperiod. Time of treatment had no effect on

node number or flower number when plants were grown under 8 or 10 hr

photoperiods.

Kaczperski et al. (1994) reported that seeds of Petunia × hybrida Ùltra White'

were germinated in #406 plug trays at 2.5°C and at a light intensity of 100 µmol s-

1m-2 using a 24 or photoperiod. At germination, seedlings were grown under

natural light conditions for 8 hrs (SD) or for 8 hrs with the photoperiod extended to

16 hrs (LD) using incandescent bulbs. At approximately the 6th leaf stage,

seedlings were stored at 5°C in the dark or at 12 µmol s-1 m-2 and a 24 hr

photoperiod for 0 to 21 days. After storage, plants were potted n 10 cm pots and

grown to flowering in a greenhouse. Plants grown under SD to the 6th leaf stage

with no cold treatment were shorter, flowered later and had more lateral branching

than un-stored LD plants. Storage at 5°C decreased time to flower of SD plants and

increased branching of LD plants regardless of photoperiod during storage.

Porat et al. (1995) reported that Celosia plumosa is a quantitative short-day plant

in which a long photoperiod of 16 h markedly delayed flowering. Increasing the

temperature regime from 17/12°C to 27/22°C (day/night) enhanced plant growth

and flower stem and inflorescence length, and shortened the time to flower

appearance. Pinching the seedlings increased the number of flower stems per plant,

but under continuous short-day conditions their growth was retarded. Pinching the

seedlings and maintaining them first for 3 weeks under non-inductive long-days to

increase their vegetative growth, and then exposing them to inductive short days,

increased the number of marketable flowering stems of suitable length. This

suggested procedure of pinching followed by a long-day/short-day photoperiod

also resulted in desirable inflorescence length with inflorescences born on stems of

sufficient diameter and strength to significantly improve flower quality.

Acock et al. (1996) studied opium poppy in chambers under a 12, 13, 14, or 24-h

photoperiod and a 12-h thermo-period of 25/20ºC. Plants at 10 or 20 days after

emergence (DAE) were transferred to separate chambers and treated for 48h with

either (a) 10ºC and a 12-h photoperiod or (b) continuous light and a 12-h thermo-

period of 25/20ºC. The 48-h interruption of each photoperiod treatment with

continuous light decreased days to flower (DTF) for photoperiods <24h for both

seedling ages, the effect being more pronounced at 10 DAE and for the 12-h

photoperiod. The 48-h 10ºC interruption had no effect on DTF. The poppy flower

was an increasingly larger proportion of the shoot biomass (from 6 to 15%) as

photoperiod increased from 12 to 24h. DTF, plant height and shoot dry weight

showed the same pattern of response to photoperiod, having minimum values in

the 24-h photoperiod treatment and increasing in values with photoperiods 14h.

Critical photoperiod, P_c, was calculated as 14.8h, by plotting DTF against

photoperiod as two straight lines and determining their point of intersection. A

similar approach using the reciprocal of DTF gave a P_c of 16h. Shoot dry weights

from all treatments were found to be an exponential function of DTF. Results

indicate that plant biomass at flowering can be estimated simply by knowing how

photoperiod and temperature affect DTF. This result presupposes that the number

of photosynthetically active days between plant emergence and flowering is the

primary determinant of biomass. If environmental conditions irretrievably limit

photosynthetic activity during this period, biomass would be overestimated.

Karlsson (1996a) planted four pansy cultivars (Crystal Bowl Deep Blue', `Majestic

Giant Blue', `Maxim Deep Blue' and Ùniversal True Blue') for 4 weeks starting 24

days after seeding, at 8 or 16 hours photoperiod and 3, 7.5 or 12 mol d–1 m–2. The

temperature was 20 ± 1°C throughout the study. The plants were allowed to flower

following the 4 weeks photoperiod treatment at 16 hours of 6 mol d–1 m–2. The first

open flower was observed significantly earlier for plants of `Majestic Giant',

`Maxim' and Ùniversal' exposed to 16 hours at 12 mol d–1 m–2 than any of the

other day lengths and irradiance levels for 4 weeks. There was no difference in rate

of flowering for plants of `Crystal Bowl' grown at 16 hours and 7.5 or 12 mol d–1

m–2. At 3 mol d–1 m–2, plant development was slowest and an 8 or 16 hours day

length did not significantly affect rate of flowering for any of the four cultivars.

Plants of `Crystal Bowl' had on average the fastest flowering (74 ± 2.2 days from

seeding with 4 weeks at 16 hours of 12 mol d–1 m–2) and plants of `Majestic Giant'

the slowest flowering (83 ± 3.4 days from seeding to flower with 4 weeks at 16

hours of 12 mol d–1 m–2) of the four cultivars.

Karlsson (1996b) grown Petunia `Midnight Madness' plants for 4 weeks starting 3

weeks after seeding, at 8 or 16 hours photoperiod and 3, 7.5, or 12 mol·d–1·m–2.

The temperature was 20 ± 1°C throughout the study. The plants were allowed to

flower following the 4 weeks photoperiod treatment at 16 hours of 6 mol·d–1·m–2.

Petunias grown at long days flowered (first open flower) faster than those exposed

to 8 hours day length for 4 weeks. Plants grown at short days required 8 to 10 more

days for flowering compared to plants grown at the same irradiance delivered

during a 16-hour day. Flowering was first observed 61 ± 0.9 days from seeding for

the plants at long days and 12 mol·d–1·m–2. Plants grown at 8 hours and 3 mol·d–

1·m–2 required on average 84 ± 0.8 days from seeding to reach flowering. The

number of flowers and flower buds (10 ± 1.8 flower buds) was lower for plants

grown at 12 mol·d–1·m–2 independent of day length. There were no significant

differences in the number of flower buds (16 ± 2.6 flower buds) at termination of

the experiment for the plants grown at the two lower irradiance levels for either 8

or 16 hours day length.

Schroeder and Stimart (1996) studied the effects of gibberellic acid (GA3) and

photoperiod in combination to reduce generation time of Antirrhinum majus L.

Four commercial inbred lines of A. majus were started from seed and grown in a

glasshouse in winter 1993-94. GA3 was applied as a foliar spray every 2 weeks at

0, 144, 289, 577, or 1155 µM starting 5 weeks after seeds were sown.

Supplemental lighting (60 µmol m–2 s–1) from 0600 to 2000 HR and night

interruption from 2300 to 0300 HR was used throughout the experiment. Data were

collected weekly on plant height and leaf count from the start of GA3 treatments

through anthesis. Time to flowering was determined as days from seed sowing to

anthesis. GA3 treatment of A. majus under a long-day photoperiod increased time

to flowering, plant height and leaf count. It would appear that long-days may have

overridden the floral induction effects of GA3.

Adams et al. (1997) investigated the effects of temperature, photoperiod and light

integral on the time to first flowering of pansy (Viola × wittrockiana Gams). Plants

were grown at six temperatures (means between 14.8 and 26.1°C), combined with

four photoperiods (8, 11, 14 and 17 h). The rate of progress to flowering increased

linearly with temperature (up to an optimum of 21.7°C) and with increase in

photoperiod (r2=0.91, 19 d.f.), the latter indicating that pansies are quantitative

long day plants (LDPs). In a second experiment, plants were sown on five dates

between July and December 1992 and grown in glasshouse compartments under

natural day lengths at six temperatures (means between 9.4 and 26.3°C). The

optimum temperature for time to flowering decreased linearly (from 21.3°C) with

declining light integral from 3.4 MJ m-2 d-1 (total solar radiation). Data from both

experiments were used to construct a photo-thermal model of flowering in pansy.

This assumed that the rate of progress to flowering increased as an additive linear

function of light integral, temperature and photoperiod. Independent data from

plants sown on three dates, and grown at five temperatures (means between 9.8 and

23.6°C) were used to validate this model which gave a good fit to the data

(r2=0.88, 15 d.f.). Possible confounding of the effects of photoperiod and light

integral are discussed

Cultan et al. (1997) placed Lamium maculatum L. `White Nancy', Scaevola aemula

R. `New Blue Wonder', Verbena × hybrida Groenl. & Ruempl. `Tapian Blue', and

Calibracoa × hybrida `Cherry Pink' under different photoperiod treatments at

constant 15, 20, 25, or 30 ± 2°C air temperature. Photoperiod treatments were 9 hr,

ambient daylight ( 8 hr) plus night interruption lighting (2200–0200 hr, 2 µmol m–

2 s–1 from incandescent lamps), or ambient daylight plus continuous light (100

µmol m–2 s–1 light from high-pressure sodium lamps). Data on plant development

and rootability of cuttings from each environment was collected. Days to anthesis

was lowest when plants were grown under the continuous lighting treatment across

species. Verbena and Calibracoa stem elongation was greatest when grown under

30°C under continuous lighting. Species were classified as to photoperiodic flower

induction groups. Implications of these data with respect to propagating and

finishing these crops are discussed.

Erwin et al. (1997) treated Petunia × hybrida Vilm. cvs. `Purple Wave', `Celebrity

Burgundy', `Fantasy Pink Morn', and `Dreams Red' with temperature and

photoperiod treatments for different lengths of time at different stages of

development during the first 6 weeks after germination. Plants were grown with

ambient light ( 8–9 hr) at 16°C before and after treatments. Flowering was earliest

and leaf number below the first flower was lowest when plants were grown under

daylight plus 100 µmol m–2 s–1 continuous light (high-pressure sodium lamps).

Flowering did not occur when plants were grown under short-day treatment (8-hr

daylight). Plants grown with night interruption lighting from 2200–0200 HR (2

µmol m–2 s–1 from incandescent lamps) flowered earlier, and with a reduced leaf

number compared to plants grown with daylight + a 3-hr day extension from 1700–

2000 HR (100 µmol m–2 s–1 using high-pressure sodium lamps). Plant height and

internode elongation were greatest and least in night interruption and continuous

light treatments, respectively. `Fantasy Pink Morn' and `Purple Wave' were the

earliest and latest cultivars to flower, respectively. Flowering was hastened as

temperature increased from 12 to 20°C, but not as temperature was further

increased from 20 to 24°C. Branching increased as temperature decreased from 24

to 12°C.

Koreman et al. (1997) exposed stock plants to alternating photoperiods to

determine if this treatment would yield many cuttings with high rooting potential.

Coreopsis verticillata `Moonbeam' and Phlox paniculata Èva Cullum' stock plants

were given 4 weeks of 4-h night interruption (NI), while Sedum Àutumn Joy'

stock plants were grown under 14-h days. After 4 weeks plants were given 0, 2, or

4 weeks of 10-h days. Cuttings were harvested and propagated under mist and three

different photoperiods (10-h, 14-h, NI) for 4 weeks, after which rooting percentage

and the number and length of roots produced by each cutting were measured.

Wang et al. (1997) reported that Argeranthemum frutescens `Butterfly' and `Sugar

Baby', Brachycome hybrid Ùltra', Helichrysum bracteatum `Golden Beauty',

Scaevola aemula `New Wonder', Supertunia axillaris hybrids `Kilkenny Bells' and

`Pink Victory', Sutera cordata `Mauve Mist' and `Snowflake', and Verbena hybrid

`Blue' were grown in a glass greenhouse maintained at 20°C under seven different

photoperiods (10-, 12-, 13-, 14-, 16-, 24-hr, and 4-hr night interruption). Black

cloth was pulled at 1700 and opened at 0800 HR; incandescent lamps provided 2

µmol·m–2·s–1 to extend light hours to the designed photoperiods. Seedlings were

pinched 3 days after transplant. Responses to photoperiod were clearly species-

dependent. The tested species can be classified into three groups: 1) stem

elongation and flowering were promoted in the long-day treatment (A. frutescens

and S. axillaris hybrids), 2) only stem elongation was promoted in the long-day

treatment (S. aemula, H. bracteatum, and B. hybrid), and 3) neither flowering nor

stem elongation were affected by photoperiod (S. cordata and V. hybrid).

Wang et al. (1997a) determined when poppy plants first become sensitive to

photoperiod and how long photoperiod continues to influence the time to first

flower under consistent temperature conditions. Plants were grown in artificially-lit

growth chambers with either a 16-h photoperiod (highly flower inductive) or a 9-h

photoperiod (non-inductive). Plants were transferred at 1 to 3-d intervals from a

16- to a 9-h photoperiod and vice versa. All chambers were maintained at a 12-h

thermo-period of 25/20 °C. Poppy plants became sensitive to photoperiod 4 d after

emergence and required a minimum of four inductive cycles (short dark periods)

before the plant flowered. Additional inductive cycles, up to a maximum of nine,

hastened flowering. After 13 inductive cycles, flowering time was no longer

influenced by photoperiod. These results indicate that the interval between

emergence and first flower can be divided into four phases: (1) a photoperiod-

insensitive juvenile phase (JP); (2) a photoperiod-sensitive inductive phase (PSP);

(3) a photoperiod-sensitive post-inductive phase (PSPP); and (4) a photoperiod-

insensitive post-inductive phase (PIPP). The minimum durations of these phases

for Papaver somniferum ‘album DC’ under the conditions of our experiment were

determined as 4 d, 4 d, 9 d, and 14 d, respectively.

Cremer et al. (1998) investigated the effect of different environmental conditions

on flowering time and the number of leaves produced before the first flower is

formed in Antirrhinum majus L. The effect of light quality has been tested by

decreasing the red/far-red ratio, generally resulting in a reduced flowering time and

leaf number. Furthermore, it could be shown that photoperiod, temperature and

light intensity are inversely correlated with flowering time and leaf number.

However, lowering the temperature from 15 to 12°C resulted in a reduction of

flowering time. This observation shows that Antirrhinum can be vernalised. Using

defined combinations of the four environmental factors we have been able to

reduce flowering time to only 42 days or to delay flowering for at least 2 years.

The results obtained allow an optimisation of the screening conditions for

identifying flowering time mutants in Antirrhinum.

Williams and Starman (1998) determined photoperiodic responses for 24

vegetatively propagated specialty floral crops. Each plant species was grown at 8-,

10-, 12-, 14-, and 16-h photoperiods. Photoperiods were provided by 8 h of

sunlight, then pulling black cloth and providing daylength extension with

incandescent bulbs. Data collected included time to flower, flower number, and

vegetative characteristics. Evolvulus nuttallianus `Blue Daze', Heliotropium

arborescens `Fragrant Delight', and Orthosiphon stamineus `Lavender' were

facultative short-day plants with respect to flowering. Time to flower increased as

photoperiod increased. Duranta repens `Blue', Verbena hybrid `Tapien Lavender',

and Verbena peruviana `Trailing Katie' were facultative long day plants with

respect to flowering. Days to visible bud and first open flower decreased as

photoperiod increased. Argeranthemum frutescens `Sugar Baby', Scaevola aemula

`Fancy Fan Falls', and Portulaca hybrid Àpricot' had increased flower number as

photoperiod increased from 8- to 16-h, although time to first flower initiation was

not affected. Abutilon hybrid Àpricot', Duranta repens `Blue', Evolvulus

nuttallianus `Blue Daze', Lotus berthelotii `Parrot's Beak', Lysimachia nummularia

Àurea Creeping Golden', Rhodanthe anthemoides `Milkyway', and Scaevola

aemula `Fancy Fan Falls' had increased vegetative growth as photoperiod

increased. All other species studied were day-neutral with regard to flowering and

vegetative parameters.

Runkle et al. (1998) studied Phlox paniculata Lyon ex Pursh 'Eva Cullum' plants

under seven photoperiods following 0 or 15 weeks of 5°C to determine the effects

of photoperiod and cold treatment on flowering. Photoperiods were a 9-hour day

extended with incandescent lamps to 10, 12, 13, 14, 16, or 24 hours; an additional

treatment was a 9-hour day with a 4-hour night interruption (NI). Non-cooled

plants remained vegetative under photoperiods ≤13 hours; as the photoperiod

increased from 14 to 24 hours, flowering percentage increased from 20 to 89.

Flowering of non-cooled plants took 73 to 93 days. Flowering percentage was 19,

50, or 100 when cooled plants were held under photoperiods of 10, 12, or ≥13

hours or NI, respectively. Time to flower in cooled plants progressively decreased

from 114 to 64 days as the photoperiod increased from 10 to 24 hours.

Reproductive cooled plants had at least three times more flowers, were at least

50% taller, were more vigorous, and developed seven or eight more nodes than did

non-cooled plants. Photoperiod had no effect on height of flowering plants.

Wang et al. (1998) recognized four phases of development from emergence to

anthesis of the opium poppy (Papaver somniferum L.) based on transfer studies

using 9- and 16-hour photoperiods: a photoperiod-insensitive juvenile phase (JP), a

photoperiod-sensitive inductive phase (PSP), a photoperiod-sensitive post-

inductive phase (PSPP), and a photoperiod-insensitive post-inductive phase (PIPP).

The objective of this experiment was to determine how the durations of the

photoperiod-sensitivity phases changed when the plants were exposed to different

photoperiods. Plants were grown in lamp lit growth chambers with a 12-hour

thermo-period of 25°C day/20°C night. They were transferred from a non-

inductive 9-h to an inductive 12-, 14-, or 16-hour photoperiod or vice versa at 1- to

4-day intervals to determine the durations of the four phases. The average number

of days to flower by plants grown continuously in a 16-hour photoperiod was 32

days. Days to flower were delayed by 10day s in the 14-hour photoperiod and by

36 days in the 12-hour photoperiod. The durations of the four phases were not

equally affected by photoperiod. The first three phases were photoperiod-

dependent the photoperiod effect being nonlinear. The durations of JP, PSP, and

PSPP were 3, 5, and 17 days in the 16-hour: 4, 8, and 23 days in the 14-hour; and

7, 14, and 40 days in the 12-hour photoperiod, respectively. The final phase was

not sensitive to photoperiod (i.e., PIPP lasted 7 days regardless of photoperiod).

Based on these results, we conclude that the so-called juvenile phase cannot be

regarded as photoperiod-insensitive. To model the development of opium poppy

under field conditions, knowledge of daylength as early as seedling emergence

may he necessary. The number of inductive cycles needed for floral induction and

the rate of floral development largely depends on the photoperiod experienced.

Garner and Armitage (1999) reported that rooted terminal cuttings and dormant 1-

year-old transplants of Phlox paniculata L. Ìce Cap' and `Red Eyes' were cooled

for 0, 4, 8, 12 or 16 weeks and forced under long-day photoperiod provided by

incandescent lights as either a night-interruption (2200–0200 HR) or extended-day

(1700–2200 HR). The influence of cooling duration, long-day lighting regime, and

propagule type on forcing days to flower, flowering stem counts, and flowering

stem length was evaluated in a 3 × 2 × 5 factorial experiment. Cooling accelerated

flowering and increased stem yield and length. Days to flower for both cultivars

decreased and flowering stems and length increased linearly as cooling increased

from 0 to 16 weeks, regardless of lighting or propagule type, but cooling for 8

weeks or more was necessary to produce marketable cut flower stems. Extended-

day lighting produced longer stems than night interruption, and stem counts were

higher among plants grown from transplants, regardless of cooling duration,

lighting regime, or cultivar. Flowering stems from rooted cuttings were generally

longer than those from transplants. Cut flower stems of Ìce Cap' were longer than

those of `Red Eyes', but days to flower and yields for the two cultivars were

similar.

Phillips et al. (1999) conducted a preliminary studies on the influence of

photoperiod, temperature, and growth regulators for H. bracteatum Vent., (syn

Bracteantha bracteata) `Sunray' and `Matilda Yellow', H. apiculatum D.C, (syn

Chrysocephalum apiculatum) `Golden Buttons' and Brachycome iberidifolia

Benth. `Jumbo Mauve' and `Mauve Delight'. All taxa of Helichrysum were

quantitative LD plants, flowering slightly more rapidly under night-break (2200-

0200 HR) and extended day incandescent lighting, compared with 9-h short-day

treatment. No influence of photoperiod occurred with cultivars of Brachycome.

Constant temperature of 12, 20, or 28°C was provided and all taxa demonstrated a

linear decrease in flowering time as temperatures increased. The growth index

(average of height and two measurements of width) was also influenced by

temperature. Paclobutrazol and daminozide were applied at different

concentrations and frequencies. Paclobutrazol was more effective than daminozide

in both genera, and daminozide was ineffective in Brachycome.

Wang et al. (1999) determined flowering time, growth, and opium gum yield from

five seed sources (T, L, B1, B2, B3) of opium poppy (Papaver somniferum L.)

collected from different latitudes in three Southeast Asian countries. Plants were

grown in six growth chambers at a 11-, 12-, 13-, 14-, 15-, or 16-hour photoperiod

with a 12-hour, 25/20 °C thermo-period. Flower initiation was observed under a

dissecting microscope (40×) to determine if time to floral initiation was identical

for all accessions across a wide range of photoperiods. The main capsule was

lanced for opium gum at 10,13, and 16 days after flowering (DAF). Plants were

harvested at 21 DAF for plant height, leaf area, and organ dry-weight

determinations. In a 16-hour photoperiod, flower initiation was observed 10 days

after emergence (DAE) for B1 vs. 8 DAE for the other four accessions. Flowering

time was affected most by photoperiod in B1 and least in B2. Flowering times for

B3, L, and T were similar across the range of photoperiods. B2, B3, and L had the

highest gum yields per capsule; even though B1 had the greatest total plant

biomass, it produced the lowest gum yield. There was no difference among

accessions in the average ratio of gum: individual capsule volume. For the ratio of

gum: capsule dry weight, only the difference between T and B1 was significant.

Capsule size did affect these ratios slightly. T had a larger gum: volume ratio for

larger capsules, and B3 had a smaller gum: dry-weight ratio for heavier capsules.

Flowering time varied up to 40%, capsule dry weight up to 41%, and opium gum

yield up to 71% for the five accessions across all treatments. No relationship was

found between flowering time and the latitude where the seed sources were

collected. Time to flower initiation could not be used to predict time to anthesis

because floral development rates varied significantly among accessions and

photoperiods. Capsule volume and dry weight were useful in estimating gum yield.

Kanellos and Pearson (2000) investigated the factors affecting the emergence and

subsequent flowering and growth of the tuberous perennial Cosmos

atrosanguineus. First experiment showed the time of emergence of overwintered

plants raised from micro-propagated tubers was highly related to temperature, but

not photoperiod, such that at 11.5°C shoots emerged 17 days later than those at

27.2°C. Subsequent growth was also significantly affected by temperature. Plant

height doubled and flower area halved as temperature increased from 13°C to

26°C. However, the response of time to flowering from emergence to temperature

was small, increasing temperature from 13°C to 21.5°C only advanced flowering

by 9 days. In terms of the overall response to photoperiod, flowering was advanced

by long-days; plants at a daylength of 17 h per day flowered 33 days earlier than

those at 8 h per day. Photoperiod also dramatically affected plant morphology,

with long photoperiods (17 h per day) leading to a greater than 7-fold increase in

plant mass compared to short-days (8 h per day). The experiments described

suggest that out of season forcing of Cosmos is horticulturally attainable at a

relatively small cost.

Pallez et al. (2000) noted that days from sowing to anthesis were significantly

different among six sunflower (Helianthus annuus L.) cultivars and ranged from 52

days for `Big Smile' to 87 days for `Pacino'. Height ranged from 13.5 cm for `Big

Smile' to 37.3 cm for `Pacino'. Postproduction life ranged from 10 days for `Pacino'

and Èlf' to 15 days for `Big Smile'. Postproduction quality ratings (1 to 5, with 5

the best) ranged from 3.9 to 5 after 5 days and 1 to 4.2 after 10 days. Quality

ratings after 15 days were not significantly different among cultivars, because few

plants were marketable at 15 days. Increasing the number of plants per pot from

one to three or five reduced number of days to anthesis and postproduction life. Pot

sizes of 10-, 13-, or 15-cm diameter, had no influence on production or

postproduction characteristics. Promalin (62.5 to 500.0 mg L–1) was not

commercially useful in extending post production life. Two cultivars were found to

be most suitable for pot production, `Pacino' and `Teddy Bear', with one plant per

15-cm pot and sprayed with B-Nine at 8000 mg L–1.

Shimai (2001) studied flowering responses in Petunia × hybrida Vilm. 'Garden

Party White' and 'Snow Cloud White' under different photoperiods and irradiance

levels. In particular, leaf number below the first flower bud (LNBFB) on the main

stem, time to macroscopic flower bud visibility (MFBV), time to anthesis, time to

flower bud development, and the percentage of flower bud abortion were

examined. LNBFB increased significantly (P<0.001) only under a combination of

shortday (SD) and low irradiance, but each had little effect alone. Time to MFBV

and time to anthesis decreased, as photoperiod or irradiance increased. One of the

main factors on late anthesis under unfavourable light condition appears to be

flower bud abortion. In this study, photoperiod or irradiance had no effect on

LNBFB, but they influenced the time to anthesis either singly or together,

indicating that longday (LD) and/or high irradiance is necessary for minimizing a

production period of petunia plants.

Donnelly and Fisher (2002b) quantified the effect of supplemental lighting on

cutting production for herbaceous annual cultivars. Stock plants of four cultivars

(Heliotropium arborescens ‘Atlantis’, Petunia ‘Supertunia Sun Snow’, Scaevola

aemula ‘New Wonder’, and Verbena ‘Tapien Soft Pink’) received ambient light

(average 156 μmol m-2 s-1 PAR during the photoperiod), or ambient light plus

either 42 or 70 μmol m-2 s-1 from high-pressure sodium (HPS) lamps for 11 hours.

In a second experiment, the same four species plus six other cultivars were grown

under ambient light (199 μmol m-2 s-1) or ambient plus 48 μmol m-2 s-1 HPS. Effect

of HPS on cutting production varied greatly between species. Growth of

Heliotropium was not significantly affected by light level in either experiment.

Petunia ‘Supertunia Sun Snow’, Scaevola, and Verbena increased cutting numbers

by 14, 51, and 12% at 42 μmol m-2 s-1 HPS and by 23%, 73%, and 22% at 70 μmol

m-2 s-1 HPS in the first experiment. In the second experiment, Petunia ‘Supertunia

Sun Snow’, Scaevola aemula ‘New Wonder’, Aloysia triphylla (lemon verbena),

and Osteospermum ‘Lemon Symphony’ had a positive cutting production response

to HPS (17-45% increase), whereas cutting numbers of other species

(Argyranthemum ‘Summer Melody’, Impatiens New Guinea hybrid ‘Pedro’,

Lantana ‘Patriot Firewagon’, Petunia ‘Supertunia Blue Wren’, and Verbena) were

not significantly affected by HPS. In both experiments, cutting quality (length,

stem caliper, fresh mass and dry mass) was not significantly affected by light level.

Erwin and Warner (2002) outlined a series of experiments that identified the

photoperiodic group classifications and responses to supplemental irradiance of 28

spring annual species. No species studied were identified as obligate short-day

plants. Most species were either obligate or facultative long-day plants. Species in

which growers have traditionally had difficulty in producing marketable flowering

plants in spring tended to be obligate long-day plants. In contrast, a number of

species that tend to flower later in the season than desirable were identified as

facultative short-day plants. In addition, species varied in their flowering response

to supplemental lighting treatments. Leaf number below the first flower was

affected by the addition of supplemental lighting under inductive conditions with

approximately one half of the species studied.

Hepworth et al. (2002) reported that flowering in Arabidopsis is controlled by

endogenous and environmental signals relayed by distinct genetic pathways. The

MADS-box flowering-time gene SOC1 is regulated by several pathways and is

proposed to co-ordinate responses to environmental signals. SOC1 is directly

activated by CONSTANS (CO) in long photoperiods and is repressed by FLC, a

component of the vernalization (low-temperature) pathway. We show that in

transgenic plants overexpressing CO and FLC, these proteins regulate flowering

time antagonistically and FLC blocks transcriptional activation of SOC1 by CO. A

series of SOC1::GUS reporter genes identified a 351 bp promoter sequence that

mediates activation by CO and repression by FLC. A CArG box (MADS-domain

protein binding element) within this sequence was recognized specifically by FLC

in vitro and mediated repression by FLC in vivo, suggesting that FLC binds

directly to the SOC1 promoter. We propose that CO is recruited to a separate

promoter element by a DNA-binding factor and that activation by CO is impaired

when FLC is bound to an adjacent CarG motif.

Huq and Quail (2002) identified a new mutant Arabidopsis locus, srl2 (short under

red-light 2), which confers selective hypersensitivity to continuous red, but not far-

red, light. This hypersensitivity is eliminated in srl2phyB, but not srl2phyA, double

mutants, indicating that this locus functions selectively and negatively in phyB

signaling. The SRL2 gene encodes a bHLH factor, designated PIF4 (phytochrome-

interacting factor 4), which binds selectively to the biologically active Pfr form of

phyB, but has little affinity for phyA. Despite its hypersensitive morphological

phenotype, the srl2 mutant displays no perturbation of light-induced expression of

marker genes for chloroplast development. These data suggest that PIF4 may

function specifically in a branch of the phyB signaling network that regulates a

subset of genes involved in cell expansion. Consistent with this proposal, PIF4

localizes to the nucleus and can bind to a G-box DNA sequence motif found in

various light-regulated promoters.

Young et al. (2003) studied four plantings of Celosia argentea var. cristata L.,

Helianthus annuus L., Zinnia elegans Jacq. in 3-week intervals and starting at the

end of February, plantings of Gladiolus × hortulanus L. H. Bailey in 2-week

intervals to determine certain characteristics of these cut flowers. Days to flower

bud, flower formation and harvest were recorded on all crops for each scheduled

planting. Days to bud decreased for Gladiolus and Helianthus in warmer

temperatures and longer daylengths, while days from bud to harvest were less for

Celosia and Zinnia for later planting dates, warmer temperatures and longer

daylengths. Postharvest longevity differences between pollen-producing and pollen

less varieties of Helianthus were determined on stems stored in a simulated interior

environment. Non-pollen producing varieties were of acceptable quality an average

of 1 to 3 days longer than pollen-producing varieties. The number of days of

acceptable quality was determined by visual observation of the first signs of petal

wilt, drop, or curl. Zinnias were harvested by two different cut stem lengths, 31 cm

and 46 cm, to determine yield differences. Plants with stems cut at 46 cm yielded

an average of 30% fewer flowers than those cut at 31 cm. The first planting of

Helianthus and Gladiolus had the best quality and highest yield, while the second

planting of Zinnia and the forth of Celosia resulted in higher quality and greater

yields.

An et al. (2004) reported that flower development at the shoot apex is initiated in

response to environmental cues. Day length is one of the most important of these

and is perceived in the leaves. A systemic signal, called the floral stimulus or

florigen, is then transmitted from the leaves through the phloem and induces floral

development at the shoot apex. Genetic analysis in Arabidopsis identified a

pathway of genes required for the initiation of flowering in response to day length.

The nuclear zinc-finger protein CONSTANS (CO) plays a central role in this

pathway and in response to long days activates the transcription of FT, which

encodes a RAF-kinase-inhibitor-like protein. We show using grafting approaches

that CO acts non-cell autonomously to trigger flowering. Although CO is

expressed widely, its misexpression from phloem-specific promoters, but not from

meristem-specific promoters, is sufficient to induce early flowering and

complement the co mutation. The mechanism by which CO triggers flowering

from the phloem involves the cell-autonomous activation of FT expression.

Genetic approaches indicate that CO activates flowering through both FT-

dependent and FT-independent processes, whereas FT acts both in the phloem and

the meristem to trigger flowering. We propose that, partly through the activation of

FT, CO regulates the synthesis or transport of a systemic flowering signal, thereby

positioning this signal within the established hierarchy of regulatory proteins that

controls flowering.

Valverde et al. (2004) reported that flowering is induced when CO messenger

RNA expression coincides with the exposure of plants to light. However, how this

promotes CO activity is unknown. They showed that light stabilizes nuclear CO

protein in the evening, whereas in the morning or in darkness the protein is

degraded by the proteasome. Photoreceptors regulate CO stability and act

antagonistically to generate daily rhythms in CO abundance. This layer of

regulation refines the circadian rhythm in CO messenger RNA and is central to the

mechanism by which day length controls flowering

Yañez et al. (2004) evaluated the effect of photoperiod on flowering response and

growth of 18 ornamental sunflower cultivars. Plants were grown in a glasshouse

under 16 h long day (LD) or 11.5 h short day (SD) conditions. In 12 of the

cultivars tested (66.7%), visible flower bud stage was significantly earlier under

the SD than the LD. All of the cultivars flowered under both the SD and the LD

conditions. However, 16 cultivars (88.9%) had a quantitative SD response, that is,

their flowering was significantly delayed under LD. Delay of flowering under LD

was variable among the cultivars, and was 14 days or greater in 11 of them.

Photoperiod had no effect on flowering of 'Jamboree'. This cultivar behaved clearly

as a day-neutral (DN) plant. The cultivar Sailor Moon showed an LD response; its

flowering was earlier under LD. In 14 of the cultivars showing an SD response,

photoperiod also influenced plant height, resulting in taller plants under LD. In

most of the cultivars there was no effect of photoperiod on flower and stem

diameters.

Corbesier and Coupland (2005) discussed molecular genetic approaches on the

function of regulatory proteins that control flowering time in Arabidopsis thaliana.

These data are compared with the results of physiological analyses of the floral

transition, which were performed in a range of species and directed towards

identification of the transmitted floral singals.

Min (2005) reviewed several recently identified signaling components that have a

potential role to integrate red, far-red, and blue light signalings. This review also

highlights the recent discoveries on proteolytic degradation in the desensitization

of light signal transmission, and the tight connection of light signaling with

photoperiodic flowering and circadian rhythm. Studies on the controlling

mechanisms of de-etiolation, photoperiodic flowering, and circadian rhythm have

been the fascinating topics in Arabidopsis research. The knowledge obtained from

Arabidopsis can be readily applied to food crops and ornamental species, and can

be contributed to our general understanding of signal perception and transduction

in all organisms.

Mizoguchi et al. (2005) observed that, in Arabidopsis thaliana, a circadian clock-

controlled flowering pathway comprising the genes GIGANTEA (GI),

CONSTANS (CO), and FLOWERING LOCUS T (FT) promotes flowering

specifically under long days. Within this pathway, GI regulates circadian rhythms

and flowering and acts earlier in the hierarchy than CO and FT, suggesting that GI

might regulate flowering indirectly by affecting the control of circadian rhythms.

We studied the relationship between the roles of GI in flowering and the circadian

clock using late elongated hypocotyl circadian clock associated 1 double mutants,

which are impaired in circadian clock function, plants over-expressing GI

(35S:GI), and gi mutants. These experiments demonstrated that GI acts between

the circadian oscillator and CO to promote flowering by increasing CO and FT

mRNA abundance. In addition, circadian rhythms in expression of genes that do

not control flowering are altered in 35S:GI and gi mutant plants under continuous

light and continuous darkness, and the phase of expression of these genes is

changed under diurnal cycles. Therefore, GI plays a general role in controlling

circadian rhythms, and this is different from its effect on the amplitude of

expression of CO and FT. Functional GI:green fluorescent protein is localized to

the nucleus in transgenic Arabidopsis plants, supporting the idea that GI regulates

flowering in the nucleus. We propose that the effect of GI on flowering is not an

indirect effect of its role in circadian clock regulation, but rather that GI also acts

in the nucleus to more directly promote the expression of flowering-time genes.

Imaizumi and Kay (2006) reported that the timing of floral transition has a direct

impact on reproductive success. One of the most important environmental factors

that affect the transition is the change in day length (photoperiod). Classical

experiments imply that plants monitor photoperiods in the leaf, and transmit that

information coded within an elusive signal dubbed florigen to the apex to

reprogram development. Recent advances in Arabidopsis research indicate that the

core of the day-length measurement mechanism lies in the circadian regulation of

CONSTANS (CO) expression and the subsequent photoperiodic induction of the

expression of FLOWERING LOCUS T (FT) gene, which might encode a major

component of florigen. In this review, we introduce current perspectives on how,

when and where the floral signal is generated.

Kurt and Bozkurt (2006) determined the effect of temperature and photoperiod on

seedling emergence of flax under controlled environmental conditions was carried

out, using the two Linum usitatissimum genotypes Windemore and San-85 and 5

temperature (10, 15, 20, 25 and 30°C) and four photoperiod (complete dark, 16 h

dark: 8 h light, 12 h dark: 12 h light and 8 h dark: 16 h light) regimes, in all

combinations. Total percent seedling emergence and seedling emergence rate of

varieties were significantly affected by the variety, temperature and variety ×

temperature interactions. The overall percent of seedling emergence of Windemore

was 29% higher than San-85. The highest emergence of seedlings was obtained at

30°C for both varieties as 96.8% for Windemore and 76.9% for San-85 and further

increase in temperature resulted in a gradual increase in seedling emergence. Less

than 40 and 30% of seedlings emergence were obtained for Windemore and San-

85, respectively, at 10°C. Seedling emergence rate was fastest at 30 and slowest at

10°C. Relatively high percent seedling emergence was obtained in a 12 h dark: 12

h light photoperiod in comparison to seedlings emerged in the other photoperiod

condition. However the photoperiod did not significantly affected either percent

seedlings emergence or seedling emergence rate. Recovery experiment confirm

that exposure of seeds to various temperature had significant effect on viability of

flax seeds whereas photoperiod had little effect on viability of flax seeds.

Pemberton and Roberson (2006) characterized the photoperiodic response in

modern seed-grown trailing-type petunia using 51 cultivars of trailing petunias

(Petunia hybrida) in plug trays. When established about 4 weeks later, uniform

plants were selected and transplanted individually to 15-cm pots. Plants were

exposed to either natural days or a 4-hour night interruption using incandescent

light from 2200 to 0200 HR each day until flowering. A minimum night

temperature of 17°C was maintained. Days to first flower from sowing ranged from

72 to 117 days. Generally, the night interruption treatment hastened flowering.

However, the degree of hastening ranged from 4 and 5 days for `Ramblin'

Burgundy Chrome' and `Ramblin' Lilac Glo', respectively, to 27 and 32 days for

`Tidal Wave Cherry' and `Tidal Wave Hot Pink', respectively.

Thomas (2006) observed that light regulates flowering through the three main

variables of quality, quantity, and duration. Intensive molecular genetic and

genomic studies with the model plant Arabidopsis have given considerable insight

into the mechanisms involved, particularly with regard to quality and photoperiod.

For photoperiodism light, acting through phytochromes and cryptochromes, the

main photomorphogenetic photoreceptors, acts to entrain and interact with a

circadian rhythm of CONSTANS (CO) expression leading to transcription of the

mobile floral integrator, FLOWERING LOCUS T (FT). The action of

phytochromes and cryptochromes in photoperiodism is augmented by ZEITLUPE

(ZTL) and FLAVIN-BINDING, KELCH REPEAT, F-BOX (FKF1) acting as

accessory photoreceptors on entrainment and interaction, respectively. Light

quality acts independently of the circadian system through Phytochromes B, D, and

E to regulate FT. Light quantity effects, on the other hand, are still incompletely

understood but are likely to be linked either directly or indirectly to patterns of

assimilate partitioning and resource utilization within the plant

Vrsek et al. (2006) discussed the possibilities of growing New England aster, cv.

September Ruby, as a flowering pot plant in the late summer period, determined

the influence of day length and the cultivar response to a single application of

daminozide in 0.2% and 0.4% concentrations upon its growth and flowering during

a period of three years. The higher values of plant height were recorded with

natural day length compared to the short day conditions. Plant diameter increases

in the first two years in the natural day length conditions. Number of buds was

larger in plants grown under natural day length than in plants grown under short

day conditions. Application of daminozide resulted in an increased number of buds

and was also efficient in reducing the internode length.

Warner (2006) determined the length of the juvenile phase and the number of

photoinductive cycles necessary to induce flowering of Cosmos bipinnatus ‘Sonata

White’ and Tagetes tenuifolia ‘Tangerine Gem’, both previously identified as

short-day plants. All plants were grown at constant 20ºC. C. bipinnatus ‘Sonata

White’, and T. tenuifolia ‘Tangerine Gem’ were grown under a non-photoinductive

long-day environment [9-h photoperiod plus night-interruption (2 µmol m-2 s-1

provided by incandescent lamps from 2200-0200 HR)], before being transferred to

a photoinductive short-day environment (9-h photoperiod) 0, 5, 10, 15, 20, or 25 d

after the first true leaf pair unfolded. Plants were grown under short days for 5, 10,

15, 20, 25 or 30 d, and then moved back to long days. Control plant groups were

maintained under short days or long days for the duration of the experiment. As

few as five short days were sufficient to hasten flowering of both C. bipinnatus and

T. tenuifolia, even for seedlings with only one leaf pair unfolded. For both species,

increasing the number of short days increased flower bud number.

Zheng et al. (2006) identified the roles of two major phytochromes (phyA1 and

phyB1) in the photoperiodic control of flowering using transgenic plants under-

expressing PHYA1 (SUA2), over-expressing PHYB1 (SOB36), or cosuppressing

the PHYB1 gene (SCB35). When tungsten filament lamps were used to extend an

8 h main photoperiod, SCB35 and SOB36 flowered earlier and later, respectively,

than wild-type plants, while flowering was greatly delayed in SUA2. These results

are consistent with those obtained with other long-day plants in that phyB has a

negative role in the control of flowering, while phyA is required for sensing day-

length extensions. However, evidence was obtained for a positive role for PHYB1

in the control of flowering. Firstly, transgenic plants under-expressing both

PHYA1 and PHYB1 exhibited extreme insensitivity to day-length extensions.

Secondly, flowering in SCB35 was completely repressed under 8 h extensions with

far-red-deficient light from fluorescent lamps. This indicates that the dual

requirement for both far-red and red for maximum floral induction is mediated by

an interaction between phyA1 and phyB1. In addition, a diurnal periodicity to the

sensitivity of both negative and positive light signals was observed. This is

consistent with existing models in which photoperiodic time measurement is not

based on the actual measurement of the duration of either the light or dark period,

but rather the coincidence of endogenous rhythms of sensitivity - both positive and

negative – and the presence of light cues.

Goto and Muraoka (2008) investigated the effects of transplant age and long-day

treatment at seedlings stage on cut flower quality of C. cristata Kurume type cv.

Sakata-pride. Plug transplants raised under 15h (natural day length) or 24-h

photoperiods in a greenhouse were transplanted into wooden containers when two,

four or eight leaves had unfolded. Flower bud initiation had already occurred in

transplants with eight unfolded leaves grown in natural but not in 24-h day length.

Days to visible bud were prolonged by 24-h treatment. The cut flowers grown in

24h were longer than those grown in natural day length. The weight of cut flower

and inflorescence decreased as transplant age increased. The inflorescence form

changed from globular to flat as transplant age increased. The youngest transplants

had the highest cut flower quality. These results suggest that in order to produce

highly marketable quality cut flowers of C. cristata Kurume type, the plug

transplants must be planted before 4 leaves unfold, and that prolonging the

seedling stage may be difficult through long-day treatment.

Garner and Armitage (2008) used rooted cuttings of Phlox paniculata L. ‘Ice Cap’

(summer phlox), which were cooled for 0, 4, 8, 12, or 16 weeks. Plants were forced

in a glasshouse averaging 18°C nights under extended-day and night-interruption

lighting from incandescent lamps providing a minimum of 14 µmol s–1 m–2 at plant

level or continuous lighting from metal halide (HID) lamps providing a minimum

of 400 µmol s–1 m–2 at plant level. The influence of cooling duration on forcing

days to flower, flowering stem counts, and flowering stem length was evaluated.

Cooling plants promoted longer stems, higher flowering stem yields, and decreased

days to flower when forced under long days provided by incandescent lamps, but

when forced under HID lamps, days to flower for cooled plants were similar to

those of non-cooled plants regardless of cooling duration. Phlox forced in extended

daylighting flowered in fewer days, had longer stems, and produced more

flowering stems than those forced in night-interruption lighting. With continuous

HID lighting, stem lengths and stems harvested per plant increased in a linear

manner as cooling increased from zero to 16 weeks. Stem lengths ranged from 63.6

cm for non-cooled plants to 96.3 cm for those receiving 16 weeks cooling, and

flowering stem yields ranged from seven stems per plant for non-cooled plants to

13 for those cooled 16 weeks. Phlox forced under HID lights flowered in

substantially fewer days and had longer stems than those forced under incandescent

lamps.

2.3 Photoperiod-sensitivity

Kiniry et al. (1983) determined the time when maize is sensitive to photoperiod.

Two photoperiod sensitive cultivars of maize were grown in controlled

environment chambers at the Duke Univ. Phytotron in photoperiods of 10, 12.5,

15, and 17.5 h. A third cultivar was grown in 12.5 and 17.5 h photoperiods. Plants

were moved at different times between chambers having different photoperiods.

Time from seedling emergence to tassel emergence was recorded. The length of

this development interval was compared to the same interval for control plants that

remained in a constant photoperiod for the entire time. The timing of photoperiod

sensitivity was determined by knowing when the plants were moved and assessing

which photoperiod affected them. Plants were insensitive to photoperiod

immediately after seedling emergence. They remained insensitive until 4 to 8 days

prior to the date of tassel initiation in short photoperiods. The insensitive, juvenile

phase, therefore ended at least 4 days prior to tassel initiation in short photoperiods.

The sensitivity continued until tassel initiation or shortly thereafter. The

photoperiod affecting development in the field, considering the slow rate of change

of photoperiod, is the value at the time of tassel initiation.

Roberts et al. (1986) recorded the durations from emergence to the appearance of

first flower buds and to first open flowers in three genotypes of lentil (Lens

culinaris Medic.) when plants were transferred from short days (either 8 or 10 h) to

long days (16 h), or vice versa, after various times from emergence. These results

were compared with those of control treatments in which plants remained in either

short or long days throughout. Four developmental phases were identified: pre-

emergence, pre-inductive, inductive and post-inductive. The first two phases and

the last are insensitive to photoperiod, but are probably sensitive to temperature.

The duration of the inductive phase, which has to be completed before flowering

can occur at the end of the post-inductive phase, can be predicted by assuming that

its reciprocal is a linear function of both photoperiod and temperature. It follows

that the critical photoperiod decreases with increase in temperature and that the

duration of the inductive phase can be calculated from a summation of the amounts

by which successive daylengths exceed the critical photoperiod until a value (‘the

photoperiodic sum’) characteristic of the genotype is reached.

Roberts et al. (1988) sown barley plants at a mean diurnal temperature of 15°C and

reciprocally transferred between different photoperiods (from 16 h d–1 to 8, 10 or

13 h d–1 or vice versa at 4, 8, 16 or 32 d after germination). Ten contrasting

genotypes were examined, including seven spring-sown types-Mona, BGS T16-2,

Athenais, Emir, Funza, USDA-016525 and S-37, and three autumn-sown types-

Gerbel B, Arabi Abiad and Ager. In the latter two all treatments were repeated on

plants grown from seeds which had been vernalized at 2°C for 42 d. The results

suggest that, between the critical photoperiod (below which there is a delay in

flowering) and the ceiling photoperiod (below which there is no further delay),

there is a linear relation between photoperiod and the reciprocal of the time taken

to flower (awn emergence). In all genotypes the ceiling photoperiod was , 10 hdd–

1; the critical photoperiod was always > 13 hdd–1 often > 14 hdd–1, and sometimes

> 16 hdd–1. All genotypes were initially insensitive to long days. At 15°C this pre-

inductive phase typically lasted for 8–10 d after germination in spring-sown types

and in vernalized autumn-sown types, but continued for more than 32 d in non-

vernalized autumn-sown types. It was followed by an inductive phase, the duration

of which depended on photoperiod, being longer in shorter days. Finally, there was

a photoperiod-insensitive, post-inductive phase, which probably began about 2

weeks before awn emergence. The low-temperature seed-vernalization treatment

considerably hastened awn emergence in Arabi Abiad and in Ager; in Arabi Abiad

low-temperature vernalization could be partly replaced by treating young plants

with short days (8 or 10 h dd–1). Both low-temperature and short-day vernalization

advanced flowering by advancing ear initiation (reducing the duration of the pre-

inductive phase), whereas long days stimulated the rate of development following

ear initiation.

Wilkerson et al. (1989) determined when different soybean [Glycine max (L.)

Merr.) genotypes first become sensitive to photoperiod and how long photoperiod

continues to influence the appearance of the first flower under optimal temperature

conditions. Controlled-environment experiments were conducted in which plants

were switched at intervals between emergence and flowering from long-day (22 h)

to short-day (9 h) treatments and from short- to long-day treatments. AH

photoperiod chambers were maintained at 26 °C both day and night. Six cultivars

from six maturity groups were used: ‘Dawson’, ‘Williams’, ‘Ransom’, ‘Forrest’,

‘Davis’, and ‘Jupiter’. Two nearly isogenic breeding lines differing in response to

inductive conditions were also evaluated. All cultivars tested were sensitive to

photoperiod by the time the unifoliolate leaf was fully expanded. The experimental

line bred for a lengthened juvenile phase exhibited apparent insensitivity to

photoperiod for 11 d longer than any of the other genotypes. After flowering was

induced, further inductive nights hastened flowering. for all cultivars, photoperiod

during the last 6.3 to 8.7 d prior to expression of the first flower had no effect on

time to first flower. Thus, for modeling purposes, the interval between emergence

and first flower can be divided into four phases: (1) a purely vegetative phase

(absent in most of the cultivars tested); (2) a photoperiod-sensitive inductive phase;

(3) a photoperiod-sensitive post-inductive phase; and (4) a photoperiod-insensitive

post-inductive phase.

Collinson et al. (1992) estimated the durations of the photoperiod-sensitive and

photoperiod-insensitive phases of development to panicle emergence in four

contrasting indica cultivars of rice (Oryza sativa L.) in a reciprocal-transfer

experiment. Plants were grown in pots in glasshouses maintained at warmer

(32/26°C) or cooler (28/20°C) day/night temperatures, and the durations from

sowing to panicle emergence were determined for plants moved from relatively

short (11 h) to relatively long (13.5 h) days and vice versa at various times after

sowing. Panicle emergence was delayed by long days in all cultivars, but the

traditional cvs Carreon and Peta were much more sensitive to photoperiod than the

modern cvs IR8 and IR36 The durations of the photoperiod-insensitive pre-

inductive phase (equivalent to some definitions of the basic vegetative phase)

varied from 14.4 d in cv. Carreon at 32/26°C to 42.0 d in cv. IR8 at 28/20°C. In all

cultivars this initial phase was of a longer duration in the cool than in the warm

regime. The duration of the photoperiod-insensitive post-inductive phase was also

consistently greater, but usually only slight so, at cool than relatively warm

temperatures; it varied from 6.8 d in cv. IR8 at 32/26°C to 272 d in cv. Carreon at

28/20°C. As expected, the length of the intervening photoperiod-sensitive inductive

phase was greater in long days, but the effect of temperature on these durations was

not consistent; for example, these durations were longer in warm than in cool

temperatures in cv. 1R8 but, if anything, they were slightly longer in cool than in

warm temperatures in cv. IR36. This difference is compatible with previous

findings that cv. IR36 has a warmer optimum temperature for rate of progress

towards panicle emergence than cv. IR8. A subsequent reciprocal-transfer

experiment with cv. Peta provided estimates of the durations of the photoperiod-

insensitive and photoperiod-sensitive phases of pre-flowering development which

were compatible with our earlier estimates. Furthermore, panicle initiation was

found to occur after about 80% of the photoperiod-sensitive inductive phase had

elapsed. We conclude that although the duration of the photoperiod-insensitive pre-

inductive phase in rice is greater than in many other annual crops, genotypic

variation in this duration may well be less than was previously deduced. We also

conclude that, despite common assumptions to the contrary, photoperiod-sensitivity

during rice plant development does not end at panicle initiation.

Ellis et al. (1992) studied plants of the quantitative short-day crop soybean

[Glycine max (L) Merrill] cv Davis in a plastic house in a diurnally alternating

temperature regime (30/20°C) and transferred from a long- (16–18 h d–1) to a short-

day regime (12 h d–1) and vice versa at various times after sowing Photoperiod

influenced the period from sowing to flowering, for example, a delay of about 50 d

between the long- and short-day controls A model was developed so as to enable

the complete data set to be analysed simultaneously in order to estimate the

durations of the photopenod-insensitive pre-inductive phase (a1), the photoperiod-

sensitive inductive phase in the short- (Is) and long-day (IL) regimes, and the

photoperiod-insensitive post-inductive phase (a3) of plant development The model

was fitted using the FITNONLINEAR directive of GENSTAT V and it described

the observations well (adjusted R2 = 0–913), the fitted values were a1 = 17 7 d (se

0.57), Is – 6 5 d (s e 0.99), IL = 55 4 d (se 281), and u3 = 19 5 d (se 0.93) The

analytical procedure developed is applicable to reciprocal transfer experiments in

other flowering plant species. The estimate of a1 for cv. Davis is substantially

greater than a previously published estimate for this cultivar, and leads us to

question the widespread assumption that all soybean cultivars respond to

photoperiod soon after emergence.

Collinson et al. (1993) studied four cultivars of soyabean [Glycine max (L.) Merill]

of diverse origin in pots in a plastic-house maintained at day/night temperatures of

30/20°C. Plants were transferred at various times after sowing from short (11·5 h d-

1) to long (13·5 h d-1) days and vice versa. The times from sowing to first flowering

for control plants grown continuously in short days varied from 38 to 53 d, whereas

the flowering of plants grown continuously in long days was delayed by about 20 d

in each cultivar. The duration of the initial photoperiod-insensitive phase (often

called the juvenile phase) varied three-fold between cultivars, i.e. from 11 to 33 d.

As expected, the duration of the photoperiod-sensitive phase was greater in long

days, but there was comparatively little genetic variation in photoperiod-sensitivity

as defined in terms of days delay in time to flowering per hour increase in

photoperiod (9-11 d h-1). Similarly, there was little variation in the photoperiod-

insensitive post-inductive phase; it ranged from 15 to 20 d. In consequence, the

duration of the initial photoperiod-insensitive phase was a strong determinant of

time to first flowering in these cultivars. The importance of this so-called juvenile

trait is discussed in terms of preventing the premature flowering of USA-adapted

cultivars when grown in short tropical daylengths and thus improving the

adaptation of the crop to the lower latitudes.

Mozley and Thomas (1995) determined the flowering responses of Arabidopsis

thaliana (L.) Heynh. L and sberg erecta (Ler) and the long-hypocotyl mutants hy2,

hy3 and hy4 were determined with respect to age, daylength and light quality. Ler

was capable of distinguishing between short days (SD) and long days (LD) from

about 4 d after sowing at 20 °C, the time at which cotyledons were expanding and

greening. At this stage, the critical daylength was between 8 h and 10 h. At 7 d,

seedlings required five LD for induction and, as the seedlings aged, they became

more sensitive so that by day 20, one LD was fully inductive. The response to SD

in newly germinated seedlings was to delay flowering without altering leaf number,

but after about 10 d, delay of flowering by SD was accompanied by extra leaves. In

light quality experiments, blue light (B) was inductive for 5-d-old plants and in all

subsequent treatments, far-red (FR) caused induction in treatments at 12 d and 18 d

and low pressure sodium, equivalent to red, was not inductive at 5 d and 12 d, but

partially inductive at day 18. Hence, both a specific blue-light photoreceptor and

phytochrome A in High Irradiance Response mode promote floral induction. In

daylength transfer experiments all three hy mutants responded to LD by earlier

flowering. Both hy2 and hy3 produced substantially fewer leaves than Ler in SD

and hy3 flowered slightly earlier than Ler. The hy4 mutants flowered later than Ler

in SD and had a higher leaf number. A scheme is proposed in which photoperiodic

induction depends on the ability of the plant to sense photoperiod, the stage of

development and the photobiological input. We also propose that phytochrome A

and the blue photoreceptor promote flowering whereas phytochrome B promotes

vegetative development.

Wang et al. (1997b) divided the development up to flowering in opium poppy

(Papaver somniferumL.) into four phases from emergence to anthesis which mark

changes in its sensitivity to photoperiod: a photoperiod-insensitive juvenile phase

(JP), a photoperiod-sensitive inductive phase (PSP), a photoperiod-sensitive post-

inductive phase (PSPP) and a photoperiod-insensitive post-inductive phase (PIPP).

To predict flowering time under field conditions, it is essential to know how these

phases are affected by temperature. Plants were grown in artificially-lit growth

chambers and received three different temperature treatments: 15/10, 20/15 and

25/20°C in a 12 h thermoperiod. Plants were transferred within each temperature

regime from a non-inductive 9 h to an inductive 16 h photoperiod or vice versa at

1–4 d intervals to determine the durations of the four phases. Temperature did not

affect the duration of the first two phases (i.e. JP lasted 3–4 d and PSP required 4–5

d). The most significant effect of temperature was on the duration of PSPP which

was 28, 20 and 17 d at 15/10, 20/15 and 25/20°C, respectively. The temperature

effect on PIPP was small (maximum difference of 3 d between treatments) and the

data too variable to indicate a significant trend. Our results indicate that PSPP is

the only phase that clearly exhibits sensitivity to temperature.

Adams et al. (1999) reported that flowering in petunias is hastened by long days,

but little is known about when the plants are most sensitive to photoperiod, or how

light integral or temperature affect such phases of sensitivity. The effect of these

factors on time to flowering was investigated using reciprocal transfer experiments

between long (16 h d-1) and short days (8 h d-1). The effect of light integral on the

phases of photoperiod sensitivity was examined using two sowing dates and a

shading treatment (53% transmission). The effects of temperature were

investigated by conducting reciprocal transfer experiments in glasshouse

compartments at five temperature regimes (means of 13.7, 19.2, 22.3, 25.0 and

28.7°C). The length of the photoperiod-insensitive juvenile phase of development,

when flowering cannot be induced by any environmental stimulus, was sensitive to

light integral; low light integrals prolonged this phase, from 23 d at 2.6 MJ m-2 d-1

to 36 d at 1.6 MJ m-2 d-1 (total solar radiation). The length of this development

phase was shortest (12.5 d) at 21°C; it was longer under cooler (21 d at 13.5°C)

and warmer temperatures (17.6 d at 28.3°C). After this phase, time to flowering

was influenced greatly by photoperiod, with long days hastening flowering by

between 28 and 137 d, compared with short days. Plants also showed some

sensitivity to both temperature and light integral during this phase, but the duration

of the final phase of flower development, during which plants were photoperiod-

insensitive, was dependent primarily on the temperature at which the plants were

grown; at 14.5°C, 33.9 d were required to complete this phase compared with 11.4

d at 25.5°C. The experimental approach gave valuable information on the phases of

sensitivity to photothermal environment during the flowering process, and could

provide the basis of a more physiologically-based quantitative model of flowering

than has hitherto been attempted. The information is also useful in the scheduling

of lighting and temperature treatments to give optimal flowering times of high

quality plants

Bertero et al. (1999) examined the effects of photoperiod on phasic development,

leaf appearance and seed growth in two cultivars of quinoa (Chenopodium quinoa

Willd.), and of photoperiod × temperature interactions on seed growth in one

cultivar. The cultivars were Kanckolla (an early-flowering cultivar from the

Andean plateau in Southern Peru) and Blanca de Junín (an intermediate flowering

cultivar from the tropical valleys of central Peru). The main objectives were to

establish which developmental phases are sensitive to photoperiod and whether

conditions during a particular phase had delayed effects on subsequent

development. Plants were grown in naturally lit growth cabinets and photoperiods

were given as 10 h of natural daylight followed by extensions with low intensity

artificial light giving either a short (SD, 10.25 h) or long (LD, 14 or 16 h)

photoperiod. Treatments were constant (SD or LD) photoperiods or involved

transfers between photoperiods at different developmental stages. A quantitative

SD response was observed for time to anthesis and total number of leaves, and

more than 50% of leaf primordia were formed after floral initiation. With transfers

effected during the reproductive phase, the maximum number of leaf primordia,

total number of leaves and time to anthesis varied by up to 9%, 33% and 24%,

respectively, in relation to controls under constant SD; and by up to 8%, 39% and

12%, respectively, in relation to controls under constant LD. Photoperiods applied

after leaf primordia initiation had ceased affected duration of the reproductive

phase and total number of leaves through effects on the proportion of primordia

that remained unexpanded (range 7–33%). Plants grown in SD until anthesis

produced seed, measured 66 days after anthesis, four-fold larger in diameter than

seed on plants always grown in LD. Seed diameter was also reduced by 24% by

LD applied after anthesis, and by 14% by high temperature (28°C cf. 21°C), but

the combination of high temperature with LD gave the greatest inhibition of seed

growth (73%). Clearly, photoperiod had strong effects on all stages of plant

reproduction and often acted indirectly, as shown by delayed responses expressed

in later phases of development.

Adams et al. (2001) stated that a quantitative understanding of the phases of

sensitivity to photo-thermal environment is important if the accuracy of flowering

models is to be improved and if the timing of long and short day treatments in

protected cropping is to be optimized. A simple method of quantifying the duration

of the phases of sensitivity to photoperiod is through the use of reciprocal transfer

experiments where plants are transferred between long and short days at regular

intervals throughout development. The advantages and disadvantages of different

analytical approaches used to analyse such data sets are examined. Inconsistencies

between the approaches are highlighted, as are differences in the way authors have

interpreted data. The problem of confounding the effects of photoperiod and light

integral is considered, as is the need to separate the number of inductive cycles

needed for flower commitment from the length of the juvenile phase.

Kantolic and Slafer (2001) investigated the relationship between the duration of the

critical period and the number of seeds produced in soybean (Glycine max (L.)

Merrill). Response to photoperiod during post-flowering stages was evaluated in

indeterminate soybean cultivars from maturity groups (MG) IV and V. The study

was conducted under field conditions with two sowing dates (normal and late).

Plants were grown under natural photoperiod throughout the experiment or

exposed, from the R3 stage (beginning pod) onwards, to artificially extended

regimes of 2 h longer than natural daylength. Duration of the R3–R6 period

increased in response to the extension of photoperiod, and cultivars of MG V

exhibited a stronger sensitivity to photoperiod than those of MG IV. Exposure to

long photoperiods promoted node production, mainly in branches, and increased

node fertility. Within each sowing date, the increased duration of R3–R6 under

longer photoperiods was corresponded with increments in pod and seed number.

Seed number was related to the duration of R3–R6, particularly when the length of

the period was corrected for temperature differences between treatments. Seed

number was also related to the integral of solar radiation during R3–R6. The

possibility of using sensitivity to photoperiod after flowering as a criterion for

increasing yields through increasing seed number are discussed.

Adams et al. (2003) developed a model that can be used to determine the phases of

sensitivity to photoperiod for seedlings subjected to reciprocal transfers at regular

intervals between long (LD) and short day (SD) conditions. The novel feature of

this approach is that it enables the simultaneous analysis of the time to flower and

number of leaves below the inflorescence. A range of antirrhinum cultivars were

grown, all of which were shown to be quantitative long-day plants. Seedlings were

effectively insensitive to photoperiod when very young (juvenile). However, after

the end of the juvenile phase, SD delayed flowering and increased the number of

leaves below the inflorescence. Plants transferred from LD to SD showed a sudden

hastening of flowering and a decrease in leaf number once sufficient LD had been

received for flower commitment. Photoperiod had little effect on the rate of flower

development. The analysis clearly identified major cultivar differences in the

length of the juvenile phase and the photoperiod-sensitive inductive phase in both

LD and SD.

Yin et al. (2005) applied a generic model for flowering phenology as a function of

daily temperature and photoperiod to predict differences of flowering times among

96 individuals (including the two parents) of a recombinant inbred line population

in barley (Hordeum vulgare L.). Because of the large number of individuals to

study, there is a need for simple ways to derive model parameters for each

genotype. Therefore the number of genotype-specific parameters was reduced to

four, namely fo (the minimum number of days to flowering at the optimum

temperature and photoperiod), 1 and 2 (the development stages for the start and

the end of the photoperiod-sensitive phase, respectively), and (the photoperiod

sensitivity). Values of these parameters were estimated using a newly described

methodological framework based on data from a photoperiod-controlled

experiment where plants were mutually transferred between long-day and short-day

environments at regular intervals. This modelling approach was tested in eight

independent field environments of different sowing dates in two growing seasons.

The four-parameter model predicted 37–67% of observed phenotypic variation in

an environment, 76% of variation in across-environment mean days to flowering

among the genotypes, and 96% of variation in across-genotype mean among the

eight environments. When all the observations of the 96 genotypes across the eight

environments were pooled, the model explained 81% of the total variation.

Sensitivity analysis showed that all four model parameters were important for

predicting differences in flowering time among the genotypes; but their relative

importance differed and the ranking was in the order of fo, , 1, and 2. This study

highlighted the potential of using ecophysiological models to assist the genetic

analysis of quantitative crop traits whose phenotype is often environment-

dependent.

Adams (2006) reviewed approaches taken to modelling time to flowering and

assesses some of the underlying assumptions that are often made. A popular

approach is to describe the effects of temperature, photoperiod and light integral as

linearly related to the rate of progress to flowering (the reciprocal of the number of

days to flower). This approach can easily incorporate both sub- and supra-optimal

temperatures and critical and ceiling photoperiods and can be modified to include

interactions where appropriate. Other workers have concentrated on modelling

temperature × photoperiod interactions using a range of mathematical functions.

Temperature averaging is discussed as this is becoming an increasingly important

part of energy saving strategies in greenhouse production. Depending on the way

in which temperatures are averaged and models are fitted, plants are often assumed

to respond to either the average or instantaneous temperature. Neither assumption

would appear to be entirely correct when plants are exposed to both sub- and

supra-optimal regimes. Furthermore, most models ignore the different phases of

flowering. Plants have distinct developmental phases and hence show changes in

their sensitivity to environmental stimuli. Many plants are photoperiodic but yet

are insensitive to daylength when juvenile and during the latter stages of flower

development.

Alcalde and Larrain (2006) evaluated a reciprocal transfers experiment (at 18.5°C

mean temperature) between long and short days and vice versa (20 and 11.5 h d−1)

with nine genotypes of pea with different allele combinations of the four major

flowering genes Lf, E, Sn and Hr, which covered the whole range of maturity

classes. Results showed that pre-flowering development in pea has three successive

phases regarding photoperiod sensitivity: a pre-sensitive (a1), a photoperiod-

sensitive (I) and a post-sensitive phase (a3). Flowering genes had their greatest

effects on the duration of the sensitive phase I. In the absence of allele Sn there was

no photoperiod-sensitive phase. Allele E, under the appropriate background for

expression, delayed and reduced the duration of the photoperiod-sensitive phase,

while allele Hr delayed the onset of the photoperiod-sensitive phase and increased

its length, especially under short days. Gene Lf with four alleles had a modifying

effect on the length of the sensitive phase. Floral initiation occurred either before

or during the photoperiod-sensitive phase, therefore in all photoperiod-sensitive

genotypes the rate of development during the early stages of flower development

was influenced by daylength. Lf and Sn were the main flowering genes influencing

time of floral initiation.

Kantolic and Slafer (2007) found that long photoperiods from flowering to

maturity delay reproductive development in soybean (Glycine max) and increase

the number of seeds per unit land area. This study was aimed to evaluate whether

sensitivity to photoperiod after flowering (a) is quantitatively related to the length

of exposure to long days and (b) persists throughout the whole pod-setting period.

It was also evaluated whether seed number was related to changes in the duration

of post-flowering phenophases. Two field experiments were conducted with an

indeterminate cultivar of soybean of maturity group V. In expt 1, photoperiods 2 h

longer than natural daylength were applied during different numbers of days from

the beginning pod stage (R3) onwards, while in expt 2 these photoperiod

extensions were imposed during 9 consecutive days starting at different times

between R3 and R6 (full seed) stages. There was a quantitative response of

development to the number of cycles with a long photoperiod. The exposure to

long photoperiods from R3 to R5 (beginning of seed growth) increased the duration

of R3–R6 regardless of the timing of exposure. The stages of development

comprised in the R3–R6 phase were delayed by current as well as by previous

exposure to long days. A positive relationship was found between seed number and

the duration of R3–R6, irrespective of the timing and length of exposure to the long

photoperiod. Sensitivity to photoperiod remained high during the reproductive

period and was highly and positively coupled with the processes of generation of

yield.

Hemming et al. (2008) examined interactions between flowering time genes in a

doubled haploid barley (Hordeum vulgare) population segregating for H. vulgare

VERNALIZATION1 (HvVRN1), HvVRN2, and PHOTOPERIOD1 (PPD-H1). A

deletion allele of HvVRN2 was associated with rapid inflorescence initiation and

early flowering, but only in lines with an active allele of PPD-H1. In these lines,

the floral promoter FLOWERING LOCUS T (HvFT1) was expressed at high levels

without vernalization, and this preceded induction of HvVRN1. Lines with the

deletion allele of HvVRN2 and the inactive ppd-H1 allele did not undergo rapid

inflorescence initiation and were late flowering. These data suggest that HvVRN2

counteracts PPD-H1 to prevent flowering prior to vernalization. An allele of

HvVRN1 that is expressed at high basal levels (HvVRN1-1) was associated with

rapid inflorescence initiation regardless of HvVRN2 or PPD-H1 genotype. HvFT1

was expressed without vernalization in lines with the HvVRN1-1 allele and HvFT1

transcript levels were highest in lines with the active PPD-H1 allele; this correlated

with rapid apex development postinflorescence initiation. Thus, expression of

HvVRN1 promotes inflorescence initiation and up-regulates HvFT1. Analysis of

HvVRN1 expression in different genetic backgrounds postvernalization showed

that HvVRN2, HvFT1, and PPD-H1 are unlikely to play a role in low-temperature

induction of HvVRN1. In a vernalization responsive barley, HvFT1 is not induced

by low temperatures alone, but can be induced by long days following prolonged

low-temperature treatment. We conclude that low-temperature and daylength

flowering-response pathways are integrated to control expression of HvFT1 in

barley, and that this might occur through regulation of HvVRN2 activity.

Karsai et al. (2008) compared the effects of synchronous photo (16 h daylength)

and thermo (2 °C daily fluctuation) cycles on flowering time with constant light

and temperature treatments using two barley mapping populations derived from the

facultative cultivar ‘Dicktoo’. The ‘Dicktoo’×‘Morex’ (spring) population (DM)

segregates for functional differences in alleles of candidate genes for VRN-H1,

VRN-H3, PPD-H1, and PPD-H2. The first two loci are associated with the

vernalization response and the latter two with photoperiod sensitivity. The

‘Dicktoo’x‘Kompolti korai’ (winter) population (DK) has a known functional

polymorphism only at VRN-H2, a locus associated with vernalization sensitivity.

Flowering time in both populations was accelerated when there was no fluctuating

factor in the environment and was delayed to the greatest extent with the

application of synchronous photo and thermo cycles. Alleles at VRN-H1, VRN-H2,

PPD-H1, and PPD-H2—and their interactions—were found to be significant

determinants of the increase/decrease in days to flower. Under synchronous photo

and thermo cycles, plants with the Dicktoo (recessive) VRN-H1 allele flowered

significantly later than those with the Kompolti korai (recessive) or Morex

(dominant) VRN-H1 alleles. The Dicktoo VRN-H1 allele, together with the late-

flowering allele at PPD-H1 and PPD-H2, led to the greatest delay. The application

of synchronous photo and thermo cycles changed the epistatic interaction between

VRN-H2 and VRN-H1: plants with Dicktoo type VRN-H1 flowered late, regardless

of the allele phase at VRN-H2. Our results are novel in demonstrating the large

effects of minor variations in environmental signals on flowering time: for

example, a 2 °C thermo cycle caused a delay in flowering time of 70 d as compared

to a constant temperature.

Yin (2008) observed the responsiveness of plant ontogeny to temperature, which

may change with plant age. These changes may best be identified by experiments

in which individual plants are transferred in a time series from low temperature

(LT) to high temperature (HT), and vice versa. Any change in the value of the

slope for a plot of the duration taken to complete a developmental phase against

time of transfer (either LT to HT or HT to LT) will indicate a change in the

temperature responsiveness of development, and the time at which this change

occurs. The analysis of this type of reciprocal-transfer experiment is usually

performed by regression for each of the visually identified linear sub-phases,

separately for the data for LT-to-HT and for HT-to-LT transfers. Here, a

mathematical approach is presented using a single curve-fitting procedure.

Methods: Both LT-to-HT and HT-to-LT transfers are combined in a single curve-

fitting procedure. This new, combined approach is illustrated using a published

data set for three rice (Oryza sativa) cultivars, where the pre-flowering duration is

divided into three sub-phases, and temperature responsiveness is generally stronger

during the second than the first and third sub-phases. This new model approach

provides an objective method, relative to the separate analyses, for assigning data

points to a particular sub-phase. Plausible parameter values can be obtained from

capturing the whole data of both sets of transfers, which otherwise could not be

obtained from the separate-analysis method. Furthermore, the length of sub-phases

identified from the LT-to-HT transfers is consistent, in terms of its response to

temperature, with that identified from the HT-to-LT transfers. Re-analysis of the

published rice data using the new approach reveals that in addition to temperature

sensitivity, the optimum temperature of pre-flowering development may vary with

plant age. The new approach gives rise to a generalized model for the analysis of

reciprocal transfer experiments to quantify age-dependent changes of response of

plants (and potentially insects) to any environmental variables that have a

significant impact on their development.

2.4 Plant height control

Talon and Zeevaart (1990) induced stem growth and flowering in the long-day

plant Silene armeria L. by exposure to a minimum of 3 to 6 long days (LD). Stem

growth continues in subsequent short days (SD), albeit at a reduced rate. The

growth retardant tetcyclacis inhibited stem elongation induced by LD, but had no

effect on flowering. This indicates that photoperiodic control of stem growth in

Silene is mediated by gibberellins (GA). The objective of this study was to analyze

the effects of photoperiod on the levels and distribution of endogenous GAs in

Silene and to determine the nature of the photoperiodic after-effect on stem growth

in this plant. The GAs identified in extracts from Silene by full-scan combined gas

chromatography-mass spectrometry (GC-MS), GA12, GA53, GA44, GA17, GA19,

GA20, GA1, GA29, and GA8, are members of the early 13-hydroxylation pathway.

All of these GAs were present in plants under SD as well as under LD conditions.

The GA53 level was highest in plants in SD, and decreased in plants transferred to

LD conditions. By contrast, GA19, GA20, and GA1 initially increased in plants

transferred to LD, and then declined. Likewise, when Silene plants were returned

from LD to SD, there was an increase in GA53, and a decrease in GA19, GA20, and

GA1 which ultimately reached levels similar to those found in plants kept in SD.

Thus, measurements of GA levels in whole shoots of Silene as well as in individual

parts of the plant suggest that the photoperiod modulates GA metabolism mainly

through the rate of conversion of GA53. As a result of LD induction, GA1

accumulates at its highest level in shoot tips which, in turn, results in stem

elongation. In addition, LD also appear to increase the sensitivity of the tissue to

GA, and this effect is presumably responsible for the photoperiodic after-effect on

stem elongation in Silene.

McDaniel (1990) compared suppression of scape elongation by paclobutrazol and

ancymidol of potted `Paul Richter' tulips (Tulipa gesneriana, L.) under greenhouse

and low light postharvest environments. Soil drench applications of paclobutrazol

at 0.25 or 0.50 mg/15-cm pot were as effective as ancymidol at 0.50 or 0.75 mg/pot

in limiting scape lengths at colored bud stage and at senescence. Paclobutrazol pre-

plant bulb soaks at 2.5 or 5.0 mg·liter-1 prevented excessive scape elongation

during low light exposure, whereas ancymidol bulb soaks were ineffective. Neither

plant growth regulator reduced flower size or affected petal color. Paclobutrazol

applied as a soil drench or as a bulb soak increased days required up colored bud

stage up to 4 days, whereas neither chemical affected post-greenhouse, life of

tulips.

Holcomb and Rose (1990) reported that bedding plants are usually grown in flats,

but if they are not moved to market on schedule, the stems elongate and the plants

become unsalable. To reduce the problem of elongation, a new growth retardant

(uniconizole) was applied to bedding plants. The bedding plants used were wax

begonia, geranium, impatiens, marigold, pansy, petunia, snapdragon, vinca and

viola. Uniconizole was applied as a foliar spray at rates ranged from 0.25 to 100

mg L-1 (active ingredient). Two classes of sensitivity to uniconizole were

established based on the growth response of the bedding plants. Class 1 was very

sensitive to uniconizole. The growth of impatiens, vinca, viola and wax begonia

was retarded adequately using uniconizole as a spray at rates of 1 to 5 mg L-1. Wax

begonia was the most sensitive to uniconizole; it required only 0.5 mg L-1 to

achieve adequate height reduction. Class 2 was less sensitive than class 1, and

required 10 to 20 mg L-1 rates for adequate height reduction. Plants in this class

were geranium, marigold, pansy, petunia, and snapdragon. Of the species tested,

snapdragon required the highest rate of uniconizole requiring at least 20 mg L-1 for

adequate height reduction.

Wang et al. (1990a) sprayed 'Connecticut King' lilies with Sumagic at 15 or 30

ppm when plants were 10 to 14 cm tall. GA4+7 was sprayed one week later at 250

or 500 ppm. The final height of the plants receiving 15 or 30 ppm Sumagic was 69

and 40 per cent, respectively, of the control plants. Sumagic at 30 ppm also

reduced leaf area and dry weight. Stem dry weight was reduced at both

concentrations of Sumagic spray. Sumagic also delayed flowering by 2 to 10 days,

shortened the duration of the flowering period of the plants by 3 to 5 days, and

reduced the length of pedicel and inflorescence. Interestingly, GA4+7 treatments

completely reversed the retarding effect of Sumagic on plant height and

inflorescence length. GA4+7 at 500 ppm alone or with Sumagic at 15 ppm reduced

days to flower. Pedicel length was longer in all the GA4+7 treatments than the

control plants. Sumagic treated plants sprayed with GA4+7 had same flower period

as the control plants.

Wang et al. (1990b) treated salvia, impatiens and petunia with Sumagic as both

spray and drench at 0.02 to 0.4 mg ai. per pot. Sumagic treatments resulted in more

compact plants in all three species compared with control. Sumagic drench was

more effective than spray in impatiens, but was similar to spray in petunia and

salvia. Sumagic generally reduced leaf area and leaf dry weight but it increased the

specific leaf weight in salvia. At high rates, Sumagic increased chlorophyll content

in all three species on a leaf area basis. On a dry weight basis, however, Sumagic

only increased the chlorophyll content in impatiens.

Latimer (1991) applied various spray rates of paclobutrazol, 5000 ppm

daminozide, 200 ppm ancymidol, or drought imposition (visible wilt symptoms for

up to 2 hours daily) to three bedding plant species to determine effects on growth

in the greenhouse and the subsequent growth and performance of treated plants in

the landscape. Seedlings of Zinnia efegans Jacq. `Peter Pan Scarlet' responded to all

growth retardants (paclobutrazol at 40 and 90 ppm) and the drought treatment in

the greenhouse. However, zinnias treated with paclobutrazol or ancymidol still

exhibited reductions in plant height 5 and 7 weeks after transplanting to the

landscape, and in plant quality (subjective rating of plant appearance with emphasis

on flower cover) at 5 weeks after transplanting. Daminozide or drought controlled

zinnia growth in the greenhouse but had no carry-over effect in the landscape. Stem

elongation of Impatiens wallerana Hook Àccent Red' seedlings was moderately

controlled by 20 ppm paclobutrazol in the greenhouse. There were no other

treatment effects in the greenhouse. Paclobutrazol (20 ppm) reduced final plant

height and quality (7 weeks postplanting). Treatment with daminozide or drought

reduced plant width and quality after 5 and 7 weeks in the landscape. Ancymidol

had no effect on landscape performance of impatiens. Shoot dry weight gain and

stem elongation of Tagetes erects L. `Papaya Crush' seedlings were reduced by

ancymidol or 40 ppm paclobutrazol in the greenhouse. Shoot dry weight gain of

marigold seedlings was inhibited during the first week of landscape establishment

by prior treatment with daminozide, ancymidol, or drought. Final plant height and

width in the landscape were not affected by any treatment; however, 40 ppm

paclobutrazol, daminozide, or ancymidol decreased final plant quality.

Rajapakse and Kelly (1991) evaluated the response of chrysanthemum cv. Bright

Golden Anne plants to GA3 and daminozide when grown under 6% CuSO4 and

water (control) spectral filters to determine the involvement of gibberellins in the

regulation of plant height under CuSO4 filters. The CuSO4 filter increased the red

(R)/far red (FR) and blue (B)/R ratio of transmitted light. Photosynthetic photo flux

(PPF) under the CuSO4 filter was reduced by about 34% compared with PPF under

the water filter which averaged about 750 micro M m-2 s-1. Control plants were

shaded with Saran Wrap to ensure an equivalent PPF to that in the CuSO4

chamber. GA3 application at 0.14 mM increased plant height under both the

control and CuSO4 filter, but the height increase under the CuSO4 filter was about

20% greater than that under the control filter. Daminozide treatment (22 mM)

reduced plant height under the control and CuSO4 filters, but the height reduction

in control plants was slightly greater than under the CuSO4 filter. The height

reduction caused by daminozide was prevented by GA3 application in plants grown

under the control or CuSO4 filter. The results suggest that GA3 may be partially

involved in height reduction under CuSO4 filters.

Svenson (1991) measured rooting and growth of Verbena cuttings (Verbena ×

hybrids Voss) were measured to determine response to foliar-applied

benzylaminopurine (BA). There was no rooting response to BA application when

visible nodal roots were present at the base of the cutting. There was no response to

30, 100, or 300 mg BA L-1 applied to the foliage 48 or 96 hours after excision from

the stock plant. Rooting-zone dry mass, total cutting dry mass, and number of roots

were increased by 30 mg BA L-1 applied immediately after excision when there

were no visible nodal roots at the base of the cuttings. Foliar application of BA at

10 or 30 mg L-1 increased lateral bud elongation of subsequently rooted shoots by

20% and 49%, respectively. Application of BA during cutting propagation to

enhance subsequent lateral bud elongation does not appear to inhibit rooting in

Verbena stem cuttings. Chemical name used: 6-benzylaminopurine (BA).

Wang and Grueber (1992) reported that control of plant height and flowering are

two major problems associated with the production of Hypoestes phyllostachya

Bak. (polka-dot plant). In seed-propagated cultivars, sprays of ancymidol (A-Rest),

chlormequat (Cycocel), paclobutrazol (Bonzi), and uniconazole (Sumagic) were

effective in inhibiting shoot growth and internode elongation at 100, 1000, 33, and

10 mg L-1, respectively. Daminozide (B-Nine), even at 6000 mg L-1, was

ineffective compared to untreated controls. Ethephon (Florel) was effective in

retarding plant growth at 500 mg L-1, but at 1500 mg L-1 resulted in leaf distortion

and horizontal shoot growth. H. phyllostachya was determined to be a quantitative

(facultative) short day plant. Seed-propagated plants with 16 or more nodes

flowered regardless of photoperiod, but flowering was more rapid under short days

(SD) than under long days (LD). Application of ethephon significantly inhibited

shoot elongation and number of flower buds formed and also increased the

incidence of flower bud abortion. In seed-propagated plants, 500 mg L-1 ethephon

did not adversely affect flowering when applied at any time during the first seven

weeks after the start of SD. At 1500 or 2500 mg L-1, ethephon applied at any time

during the first five weeks after the start of SD maximized the number of

vegetative buds and minimized the number of viable flower buds. When applied

more than six weeks after SD began, ethephon did not promote the formation of

vegetative axillary buds but did promote flower bud abortion

Rajapakse et al. (1992a) evaluated the response of `Bright Golden Anne' and

`Spears' chrysanthemum plants to EOD-R or FR light to determine the involvement

of phytochrome in regulation of plant morphology under CuSO4 filters. Light

transmitted through the CuSO4 filter significantly reduced height, internode length

and stem dry weight of `BGA' and `Spears' chrysanthemum plants. However, the

degree of response varied with the cultivar. Exposure to EOD-FR reversed the

reduction of plant height, internode length and the stem dry weight caused by the

light transmitted through CuSO4 filters to a level comparable with control plants.

Exposure to EOD-FR did not significantly alter height and stem dry weight under

control filter Exposure to EOD-R light reduced the height and stem dry weight of

`BGA' plants grown under control filter but EOD-R had no effect under CuSO4

filters. In `Spears' plants, EOD-R caused stem dry weight reduction under control

filters, but did not reduce stem or internode elongation. The results suggest

phytochrome may be involved in controlling plant response under CuSO4 filters.

However, there are evidences to indicate that an additional mechanism may be

acting on stem/internode elongation.

Rajapakse et al. (1992b) Experiments were conducted to correlate the response of

chrysanthemum [Dendrathema × grandiflorum (Ramat.) Kitamura] plants to light

environment based on various quantitative light quality parameters by growing

plants under 6% or 40% CuSO4 and water spectral filters. Using a narrow band

width (R = 655-665 and FR = 725-735 nm) or a broad band width (R = 600-700

and FR = 700-800 nm) for R: FR ratio calculation, 6% CuSO4 filter transmitted

light with a higher R: FR ratio than 40% CuSO4 or water filters. Light transmitted

through 40% CuSO4 and water filters had similar narrow band R: FR ratios ( 1.2),

but the broad band R: FR ratio (2.0) of 40% CuSO4 filter was higher than that of

water filters. The estimated phytochrome photoequilibrium ( ) value varied

considerably with the photochemical properties of phytochrome used for

estimations. Final height and internode length of plants grown in 6% or 40%

CuSO4 chambers was 30% less than of plants in corresponding control chambers.

Leaf and stem dry weights were reduced by light transmitted through CuSO4

filters. The results suggest that broad band R: FR ratio correlated more closely to

above plant responses than the narrow band R: FR ratio. Blue (B): R and B: FR

ratios (not absolute amount of blue wavelengths) correlated well with plant

response, suggesting that involvement of blue light should not be ignored in

expressing plant response to light transmitted through CuSO4 filters. At present, the

presentation of complete spectral data would be the most useful in explaining plant

response to light environment.

Heins and Fisher (1992) developed a computer decision support tool, the Poinsettia

Care System, to combine graphical display of plant height with an expert system to

provide height control advice. A simulation model is used to predict future growth

of the crop based on greenhouse temperature, growth retardant applications, plant

spacing, plant maturity, and light quality. Growth retardant and temperature

recommendations are made based on a crop's deviation from the target height,

expected future growth rate, and crop maturity. The program was beta tested by 8

Michigan growers over the 1991 poinsettia season. The test growers reacted

positively to the program in a follow-up survey. Perceived benefits included

improved height control, consistent crop recording, and a `second opinion' when

making height control decisions.

Cramer and Bridgen (1993) evaluated three growth regulators and concentrations

capable of reducing plant height in Mussaenda. Daminozide (B-Nine SP),

ancymidol (A-Rest), or paclobutrazol (Bonzi) was applied at two concentrations

each. Daminozide was tested as a spray at 2500 ppm and 5000 ppm. Ancymidol

was applied as a spray at 33 ppm and 66 ppm or as a drench at 0.25 mg per pot and

0.50 mg per pot. Paclobutrazol was tested as a spray at 25 ppm and 50 ppm or as a

drench at 0.125 mg per pot and 0.25 mg per pot. Growth regulators were applied as

a single application or a double application with two weeks separating applications.

Daminozide at 2500 ppm and 5000 ppm was most effective in controlling plant

height. Ancymidol as a drench at 0.25 mg per pot and 0.50 mg per pot was also

effective in plant height control. Two applications of these growth regulators were

more effective in controlling plant height than a single application.

Krausz et al. (1993) evaluated the effects of post-emergence clethodim (112 g ha-

1), fenoxaprop (140 g), fluazifop-P (210 g), haloxyfop (140 g) and quizalofop (90

g) applied for S. faberi control at 4 plant heights in soybeans cv. Williams 82. All

herbicides controlled 84-99, 85-99, 74-99 and 95-99% of 7, 15, 30 and 60 cm S.

faberi in all 3 years. Control of 7, 15 and 30 cm S. faberi with fenoxaprop,

fluazifop-P, quizalofop and sethoxydim was dependent upon soil moisture

conditions at application. Clethodim and haloxyfop resulted in the greatest control

(89-99%) regardless of plant height or soil moisture conditions. No herbicide

injured soybeans and all increased soybean grain yields from untreated control

values of 1310-2740 kg ha-1 to 1360-3180 kg.

Wilfret and Harbaugh (1993) studied Pentas (P. lanceolata Benth.) cv. Ruby Glow

Red single node cuttings grown in 15 cm pots in a glasshouse and developing

laterals were pinched to one node. Plants were sprayed with chlormequat (CCC) at

0, 500, 1000, 1500, or 2000 ppm on 5, 10, or 15 days after pinching. An ancymidol

(0.5 mg ai/15 cm pot) drench treatment was applied at the above 3 dates.

Application date had no effect on plant height and ancymidol had minimal effect.

All CCC treated plants were shorter than controls but little differences were

recorded among CCC conc. Since most stem elongation occurred after the

inflorescence was ca. 2 cm diam., a second experiment with similarly grown plants

consisted of CCC sprays of 0, 500, 1000, 2000, or 4000 ppm applied 10 days after

pinching. Additional CCC applications were made when the inflorescence was 2

cm diam. All treatments yielded plants shorter than controls which were 57 cm.

Plants sprayed initially with CCC at 2000 ppm plus CCC at either 500, 1000, or

2000 ppm at the bud stage ranged from 28 to 32 cm tall, an ideal height range for

15 cm pots. CCC at 4000 ppm appeared to reduce stem turgidity and the

inflorescence tended to droop at maturity.

Brian and Hammer (1994a) determined the suitability of paclobutrazol to control

height of mini-poinsettias. Cuttings of poinsettia cultivars Freedom and Red Sails

were taken on 10 Sept. and rooted under mist. On 11 Oct. when short days began,

plant height was measured and 4 plant growth regulator (PGR) treatments were

applied as foliar sprays using a volume of 204 ml m-2: paclobutrazol at 15, 30, 45

and 60 mg L-1, plus an untreated control. At anthesis, plant height (pot rim to top of

plant) and bract diameter (measured in 2 directions and averaged) were measured.

Data for plant height gain (PHG), the difference between plant height at anthesis

and when PGRs were applied, and bract diameter were analyzed statistically. PHG

was significantly different at the cultivar × treatment interaction. For `Red Sails' all

paclobutrazol treatments significantly retarded PHG, but there were no significant

differences in PHG with increased rates of application. For `Freedom' only

paclobuuazol rates at 30 and 45 mg L-1 significantly retarded PHG. Bract diameter

was significantly different at paclobunazol rates 30 mg L-1 or greater, with

diameter decreasing as the rate of PGR applied increased

Whipker and Hammer (1994b) conducted field studies on the potential of annual

statice as an outdoor cut-flower crop. Data showed that yellow cultivars had more

stems harvested than the rose, apricot, and blue cultivars, but stems of the yellow

cultivars weighed less. The number of stems harvested over time tended to be

concentrated in the first 8 weeks after flowering begins. In 1990, the average stem

fresh weight was significantly different among the apricot, blue, and rose cultivars,

but the number of stems harvested was significantly different only between the

blue and rose cultivars.

Cramer and Bridgen (1994) determined the effects of three growth regulators at

two concentrations each, as well as the application method and the number of

applications on Mussaenda plant height. Three growth regulators, daminozide (B-

Nine), ancymidol (A-Rest), and paclobutrazol (Bonzi) were applied at two

commercially recommended rates and two application methods (spray or drench).

The treatment were daminozide at 2500 ppm and 5000 ppm (spray), ancymidol at

33 and 66 ppm (spray) and at 0.25 and 0.50 mg per pot (drench), and paclobutrazol

at 25 and 50 ppm (spray) and at 0.125 and 0.25 per pot (drench). In subsequent

experiments, the same growth regulators were applied with an increase in

concentration and either two or three applications. The treatments were daminozide

at 5000 ppm (spray), ancymidol at 66 and 132 ppm (spray) and at 0.50 and 1.0 per

pot (drench), and paclobutrazol at 50 and 100 ppm (spray) and at 0.25 and 0.50 per

pot (drench). The most attractive potted plants were produced with two

applications of daminozide at 5000 ppm or two applications of ancymidol at 0.5 per

pot (drench). Higher concentrations or additional applications excessively reduced

plant height. Three spray applications of 132 ppm ancymidol also produced an

attractive potted plant. Paclobutrazol sprays or drenches at any concentration or

application number were ineffective for reducing Mussaenda `Queen Sirikit' plant

height.

Blom et al. (1994) studied potted plants of Lilium longiflorum Thunb. cvs. Àce'

and `Nellie White' grown either under an ambient photoperiod (APP) or under an

8-hour photoperiod (8PP) in a greenhouse. The latter photoperiod was achieved by

pulling black cloth over the plants at 1615HR and removing the cloth at 0615HR

each day, from emergence to flowering. Within each photoperiod, ambient light

intensity was reduced by 0, 20, 40 or 60% using various shade cloths permanently

suspended above the plants. Heating was set at 20/16oC for the dark/light period,

respectively. Plant height, determined from the rim of pot to the top of plant, was

25% lower under 8PP compared to APP for both cultivars. Plant height of Àce'

and `Nellie White' increased by 1.5 mm and 2.5 mm, respectively, per 1% light

reduction.

Incrocci et al. (1994) described a series of experiments performed with the aim of

exploiting the possibilities of using high R/FR light, obtained with copper sulphate

filters, as an environmentally friendly technique for the control of plant height.

Plantlets of Salvia splendens were grown under growth chambers made with

polycarbonate panels filled with water and a solution of commercial copper

sulphate at 8%. The light filtered by water panel filters decreased only the light

level, while the copper sulphate filter induced lower level of light and an higher

R/FR. ratio in comparison to water filter and greenhouse natural light. The

experiment consisted of four different treatments: plants under water filter panel

(W), under water filter panel + 15 minute-supplementary-end-of-day red light

(W+R) and under copper sulphate growth chamber (all at the same Photosynthetic

Photon Flux, P.P.F.) and plants placed in greenhouse. The copper sulphate-induced

reduction of plant height was between 22–48 %, depending on the environmental

light conditions, but plant height was never shorter than greenhouse control. It

appears, that, in our experimental conditions and for this plant, is not possible to

suggest the use of copper sulphate filter as a valid technique for the reduction in

plant height.

Blom et al. (1995) studied potted bulbs of Lilium longiflorum Thunb. Àce' and

`Nellie White' and Lilium (Asiatic hybrid) Ènchantment' grown in a greenhouse

under ambient photoperiod (APP), 8-h photoperiod by removing twilight from

ambient by blackout cloth (8PP), or 8PP extended with 1 hour of low-intensity far-

red radiation (9PP). Height of Àce', `Nellie White', and Ènchantment' increased

by 24%, 18%, and 12%, respectively, under APP and by 118%, 100%, and 44%,

respectively, under 9PP compared to 8PP. In a second experiment, the effects of

reduced irradiance (0%, 25%, 50%, and 75% shade) were determined on the same

cultivars grown under APP or 8PP. The effects of APP on height were similar in

magnitude for Àce' and `Nellie White' but were insignificant for Ènchantment'

compared to 8PP. Shading increased height linearly for all cultivars. The regression

was greater under APP (2.8 mm per percent shade) than under 8PP (1.8 mm per

percent shade) for Àce' and `Nellie White' combined. Plant height of

Ènchantment' was less affected by reduced irradiance. For all cultivars, APP or

9PP produced higher stem dry weight compared to 8PP. Shading decreased leaf and

bulb dry weight of the Easter lily cultivars.

Whipker and Hammer (1995) applied chemical plant growth retardant (PGR)

treatments (mg L–1) as foliar sprays to three zonal geranium cultivars: chlormequat

at 1500, applied two, three, and four times, a combination of chlormequat at 750

and daminozide at 1250, applied one and two times, and paclobutrazol applied

once at 5, 10, 20, and 30; twice at 5, 10, and 15; and three times at 5, plus an

untreated control. Two paclobutrazol drench treatments at 0.1 and 0.25 mg a.i. per

pot were also applied. The results of the PGR applications were significant at the

cultivar × treatment interaction for leaf canopy height and plant diameter.

Paclobutrazol rates of 10 to 15 mg L–1 resulted in acceptable height control for

`Medallion Dark Red' and Àurora'. `Pink Satisfaction' is a less vigorous cultivar

and lower paclobutrazol rates of 5 to 10 mg L–1 were more suitable. When the total

concentration of the single and multiple applications were compared, no additional

height control was realized with the multiple applications of paclobutrazol.

Barrett et al. (1995) evaluated paclobutrazol drench treatments for efficacy on

Caladium × hortulanum (Birdsey) cultivars Aaron, White Christmas, and Carolyn

Wharton. Drenches at 2.0 mg per pot did not reduce height of Àaron' and `White

Christmas' plants when applied 1 week after planting, but 2.0 mg applied at 3

weeks after planting did result in shorter plants. The difference for time of

application may be due to the amount of roots present to take up paclobutrazol

when applied. In two factorial experiments, there were no interactions between

cultivar and time of application or amount of chemical. Paclobutrazol at 0.5 mg per

pot resulted in plants that were shorter than the controls. Higher amounts of

paclobutrazol provided additional reductions in height, but there was variation

between the experiments for degree of effect with amounts >1 mg. Generally,

commercially acceptable height control was provided by paclobutrazol drench

treatments at 0.5 and 1.0 mg per pot applied 3 weeks after planting.

Karlsson and Nilsen (1995) reported that Ùltra Rose Star' petunia plants were

germinated and grown at 21oC. The study was initiated 26 days after seeding and

the photoperiod was 15 h of light and 9 h of darkness. During the initial or ending

90 min of the light period, the plants were exposed to a light quality of a higher (

2.0) or lower ( 0.8) red (R, 660 nm) to far red (FR, 730 nm) ratio than daylight (R:

FR, 1.1). Flowering occurred within 65 days from seeding for plants in all

treatments. Plants receiving a low R: FR during the initial 90 min of the day had

similar internode lengths as those plants receiving a high R: FR at the end of the

day. The average internode length of the main stem at flowering was 0.6 ± 0.08 cm

for plants receiving a low R: FR in the morning or a high R: FR at the end of the

day. In addition, the internodes of those plants exposed to a low R: FR in the

morning were longer than on plants receiving a low R: FR at night or a high R: FR

in the morning. The average internode length at flowering was 0.4 ± 0.08 cm for

plants with an ending low R: FR or a beginning high R: FR light quality of the day.

Shaw et al. (1995) observed that one-time application of fish emulsion 2 days

before the application of plant growth regulators (PGR) showed an overriding

effect on the growth of pansies. Blue/blotch shades of `Medallion' pansies were

placed on a constant feed program of 100 ppm Peat Lite 20N–10P–20K, with half

of the pansies receiving an additional one-time supplement of fish emulsion. PGRs

and rates included B-Nine, 0.5% (used as the control); uniconazole, 2 and 4 ppm;

and paclobutrazol, 16 and 25 ppm. Parameters taken included plant height, top

fresh weight, top dry weight, days to anthesis, and visual appearance. Significant

differences were noted in the plants receiving the supplement for plant dry weight,

plant height, and visual appearance. Plants receiving fish emulsion grew taller and

denser than those on constant feed alone despite the effects of the PGRs.

Reddy and Rajapakse (1995) investigated the influence of removal of specific

wavelengths [red (R), blue (B), and farred (FR)] from sunlight on the height of

chrysanthemum plants was investigated by overlaying RoscoluxTM colored acetate

films on 4% CuSO4 or water (control) spectral filters. CuSO4 filters removed FR

wavelengths and significantly reduced plant height and internode length compared

to control plants that received B, R, and FR wavelengths of light. Plants grown

under Roscolux blue filters did not receive R light and were significantly taller

compared to plants from any other treatments. Plants grown under Roscolux red

filters did not receive B light and were significantly shorter compared to plants

from other treatments. Leaf area, leaf dry weight and stem dry weight were highest

in plants grown under Roscolux red and control filter combination. The amount of

leaf chlorophyll and the ratio of Chl A: Chl B was highest in plants grown under

Roscolux blue filters. In general, plants that received FR light (control + film) were

taller than the plants that did not receive FR light in the corresponding (CuSO4 +

film) filter combination.

Whipker and Hammer (1996) applied plant growth retardant (PGR) media drench

treatments (in mg a.i. per pot) of ancymidol at 0.5, 1.0, 2.0, 4.0, or 8.0;

paclobutrazol at 1.0, 2.0, 4.0, 8.0, or 16.0; uniconazole at 0.5, 1.0, 2.0, 4.0, or 8.0 to

tuberous-rooted dahlias to compare their effectiveness as a chemical height control.

All paclobutrazol, ancymidol, and uniconazole rates applied significantly reduced

`Red Pigmy' plant height by 21% or greater compared to the nontreated control.

Excessively short plants resulted from uniconazole and ancymidol drench rates

1.0 mg. `Red Pigmy', a less vigorous cultivar, were acceptable as potted-plants

with paclobutrazol rates of 2.0 to 4.0 mg, 0.25 to 0.5 mg of uniconazole, or 0.5 mg

of ancymidol. All paclobutrazol, ancymidol, and uniconazole rates significantly

reduced `Golden Emblem' plant height by 11% when compared to the nontreated

plants. Excessively short plants resulted from paclobutrazol drench rates of 16.0

mg, uniconazole rates of 2.0 mg and for ancymidol drenches 4.0 mg. `Golden

Emblem', the more vigorous cultivar, were acceptable as potted-plants with

paclobutrazol rates of 4.0 to 8.0 mg, 0.5 to 1.0 mg of uniconazole or 2.0 mg of

ancymidol.

Hamaker et al. (1996a) determined the effectiveness of five growth retardants on

final plant height and flowering of herbaceous perennials. Growth retardant

treatments consisted of five sprays: 100 ppm ancymidol, 1500 ppm chlormequat,

5000 ppm daminozide, 30 ppm paclobutrazol, or 15 ppm uniconazole. Also

included for comparison were two drenches of 15 ppm paclobutrazol or 7.5 ppm

uniconazole. Spray treatments consisted of one application every 10 days until

anthesis. Drench treatments consisted of one application only. Data for days to

visible bud and anthesis, bud number, and final height were collected. Plant

response varied significantly between growth retardant treatments. Sprays of

ancymidol, chlormequat, daminozide, paclobutrazol, and uniconazole effectively

controlled the height of 4, 3, 13, 4, and 12 species, respectively. Daminozide and

uniconazole were the most effective sprays at controlling height on a broad range

of species. However, daminozide delayed anthesis compared to control treatments

of at least 5 species. Drench treatments of paclobutrazol and uniconazole were

effective on 14 and 15 species, respectively. The number of responsive species

increased significantly when paclobutrazol was used as a drench rather than a

spray. All species tested were responsive to at least one growth retardant treatment.

Hamaker et al. (1996b) determined the effect of DIF and temperature drop on final

height for eight species of perennials. Durations for DIF temperatures were 12

hours for both DT and NT. Temperature alterations occurred at sunrise.

Temperature treatments (DT/NT) consisted of zero DIF (20/20°C), negative DIF

(16/24°C), or positive DIF (24/16°C), and a 2-hour drop (12.7/20.7°C). Long days

(LD) were provided from 2200-0200 HR by either cool-white fluorescent (CWF)

or incandescent (INC) lights. Data for days to visible bud and anthesis, bud

number, and final height were collected. Positive DIF conditions enhanced

elongation while negative DIF reduced it in all species. As DIF decreased from

positive to negative, plant height was reduced 10%, 30%, 30%, and 20% in

Coreopsis `Moonbeam' and `Sunray', Delphinium `Belladonna', and Scabiosa

`Butterfly Blue', respectively. Negative-DIF responses were enhanced under CWF

lights for some species. In negative-DIF conditions, Coreopsis `Moonbeam' and

`Sunray' and Delphinium `Belladonna' were 10%, 10%, and 15% shorter,

respectively, under CWF lights than INC lights.

Whipker and Dasoju (1997) applied plant growth retardant (PGR) foliar spray

treatments (mg L–1) of daminozide at 1000 to 16,000; paclobutrazol from 5 to 80;

and uniconazole from 2 to 32 to `Pacino' pot sunflowers (Helianthus annuus) to

compare their effectiveness at chemical height control. When the first inflorescence

opened, the number of days from seeding until flowering, total plant height

measured from the pot rim to the top of the inflorescence, inflorescence diameter,

and plant diameter were recorded. Total plant height, plant diameter, inflorescence

diameter, and days until flowering were significant for the PGR treatment

interaction. Marketable-sized plants grown in the 1.2-liter pots were produced with

uniconazole concentrations between 16 and 32 mg L–1 or with daminozide

concentrations between 4000 and 8000 mg L–1. Paclobutrazol foliar sprays up to 80

mg L–1 had little effect and higher concentrations or medium drench treatments

should be considered.

Dasoju and Whipker (1997) applied drench applications of plant growth retardant

paclobutrazol at 2, 4, 8, 16, or 32 mg a.i. per pot, plus an untreated control to pot

sunflowers (Helianthus annuus cv. `Pacino') to determine its effect as a chemical

height control. All paclobutrazol concentrations applied significantly reduced plant

height by »27% when compared to the untreated control, but excessively short

plants were observed at 16 and 32 mg a.i. per pot. Plant diameter was also

significantly decreased by »16% at 2 and 4 mg a.i. per pot of paclobutrazol, when

compared to the untreated control. Flower diameter decreased by »4% at 2 and 4

mg a.i. per pot of paclobutrazol, but only concentrations 4 mg a.i. per pot were

significantly different from the untreated control. Paclobutrazol concentrations had

no effect on days from potting to flowering. Drench concentrations of 2 and 4 mg

a.i. per pot of paclobutrozol produced optimum height control in relation to 16.5-

cm-diameter pot size used.

Berghage (1998) reported that plant height is a function of the number of nodes

and the length of each internode, and both are strongly influenced by greenhouse

temperatures. Node number, or formation rate, is primarily a function of the

average greenhouse temperature, increasing as the average temperature increases.

Internode length is strongly influenced by the relationship between the day and

night temperature, commonly referred to as DIF (day temperature - night

temperature). As DIF increases, so does internode length in most plant species

studied. Although the nature and magnitude of temperature effects vary with

species, cultivar, and environmental conditions, these two basic responses can be

used to modify transplant growth. Although data are limited, controlling transplant

height with temperature does not appear to adversely influence plant establishment

or subsequent yield.

Cramer and Bridgen (1998) examined Mussaenda as a potential potted floriculture

crop because of its showy white, picotee (white with pink margins), pink or red

sepals and fragrant, yellow flowers. However, the profuse upright growth habit of

some Mussaenda cultivars is undesirable for pot plant culture. Three growth

regulators, daminozide (B-Nine), ancymidol (A-Rest), and paclobutrazol (Bonzi),

were applied at two commercially recommended rates and two application methods

(spray vs. drench) to determine their effects on plant height. Treatments (all

concentrations as active ingredients) were daminozide spray (2500 or 5000 mg L-

1), ancymidol spray (33 or 66 mg L-1), ancymidol drench (0.25 or 0.50 mg per pot),

paclobutrazol spray (25 or 50 mg L-1), and paclobutrazol drench (0.125 or 0.25 mg

per pot). In subsequent experiments, the same growth regulators were applied at

higher concentrations and in either two or three applications. The most attractive

potted plants were produced with two spray applications of daminozide at 5000 mg

L-1 or two drench applications of ancymidol at 0.5 mg per pot. Higher

concentrations or additional applications excessively reduced plant height.

Paclobutrazol sprays or drenches at any concentration or application number were

ineffective for controlling plant height.

Chronopoulou-Sereli et al. (1998) investigated the effects of paclobutrazol (5, 10

or 20 ppm) and triapenthenol (70, 140 or 280 ppm) on growth and flower number

of G. jasminoides plants in relation to temperature and solar radiation under

greenhouse conditions. Growth was significantly retarded in plants treated with

growth retardants. High concentrations of growth retardants reduced flower

number. No significant differences in flower number were observed between the

control and plants treated with the low concentrations of growth retardants. High

correlation coefficients were found between plant height (for control plants and

those treated with the lowest doses), mean air temperature and total solar radiation.

The best quality plants for sale were those treated with triapenthenol at 70 ppm

(height reduced by 55% compared with the control, but the number of flowers was

the same as the control).

Kessler and Keever (1998) reported that rooted terminal cuttings produced under

short days were given a terminal pinch and transplanted to 10 cm pots. Cuttings

were sheared to 6 cm above the pot rim 4 weeks later. Growth retardant treatments

consisting of ancymidol drench at 0, 0.125, 0.25, or 0.375 mg a.i./pot;

paclobutrazol drench at 0, 0.125, 0.25, or 0.375 mg a.i./pot; daminozide spray at 0,

2550, 5100, or 7650 mg·L–1; paclobutrazol spray at 0, 12, 24, 36, 48, or 60 mg L–1;

or flurprimidol spray at 0, 25, 50, 75, 100, 150, or 200 mg L–1 were applied 10 days

after shearing. Night-breaking lighting using incandescent bulbs was started the

same day. The highest rate of ancymidol, paclobutrazol drench, daminozide, and

flurprimidol decreased plant height compared to controls by 36, 30, 21, and 36%,

respectively. Paclobutrazol sprays were not effective. A market quality rating of

four or higher (good, salable) was given to plants treated with daminozide at 5100

or 7650 mg L–1 or flurprimidol at 150 or 200 mg L–1. A second experiment was

conduced to determine application timing. A daminozide spray at 0, 2550, 5100, or

7650 mg L–1 was applied 0, 3, 6, 9, 12, or 15 days after shearing. Plant height,

growth index and lateral shoot length were least and market quality rating highest

when 5100 or 7650 mg L–1 of daminozide was applied between 6 and 9 days after

shearing.

Ranwala and Miller (1999) investigated the effects of Promalin® [PROM; 100 mg

L–1 each of GA4+7 and benzyladenine (BA)] sprays on leaf chlorosis and plant

height during greenhouse production of ancymidol-treated (two 0.5 mg drenches

per plant) Easter lilies (Lilium longiflorum Thunb. `Nellie White'). Spraying with

PROM at early stages of growth [36 or 55 days after planting (DAP)] completely

prevented leaf chlorosis until the puffy bud stage, and plants developed less severe

postharvest leaf chlorosis after cold storage at 4°C for 2 weeks. When PROM was

sprayed on plants in which leaf chlorosis had already begun (80 DAP), further leaf

chlorosis was prevented during the remaining greenhouse phase and during the

postharvest phase. PROM caused significant stem elongation (23% to 52% taller

than controls) when applied 36 or 55 DAP, but not when applied at 80 DAP or

later. The development of flower buds was not affected by PROM treatments.

Although PROM sprays applied at 55 DAP or later increased postharvest flower

longevity, earlier applications did not.

Holt and Jennings (1999) transplanted rooted chrysanthemum cuttings of five

cultivars into 6 1/2'' pots and greenhouse-grown for 7 weeks under natural

daylength conditions. Plants were pinched back twice, on the 3rd week and the 5th

week following transplanting. At 7 weeks, plants were arranged in a complete

randomized-block design with four plants per cultivar per treatment and three

replications. Spacing of the pots was kept constant through the duration of the

experiment. The chemical group was sprayed with 2500 ppm B-Nine until run-off

on the first day of treatment. The mechanical group was brushed 40 times, twice a

day, for 5 weeks. The brushing mechanism was adjusted daily to account for

growth so as to stimulate only the top 2 to 3 inches of the plant. Measurements of

all plants were taken on the first and last day of the mechanical treatment. Data

collected included height, internode length, and leaf area. Plants were then allowed

to flower under the naturally shortening daylength, and the flowering date was

recorded. The chemical and mechanically treated plants were shorter than the

controls with a greater response occurring with the cultivars Èmily' and `Cheery

Emily', which had a more open and upright growth habit.

Shaw et al. (1999) evaluated seedlings of Celosia plumosus `New Look', a new

variety for their response to the recommended rates of three different plant growth

regulators commonly used by growers. The plant growth regulators were B-nine,

paclobutrazol, and uniconizole. These plant growth regulators were applied at the

rate recommended by the manufacturer for this species. Group I, the control, was

not treated with a plant growth regulator, but was sprayed with water at the same

time the other treatments were applied. Plants were grown in 5 inch plastic pots in

the greenhouse. Plant height was recorded before treatment and once weekly

thereafter for the duration of the experiment. Upon termination of the experiment,

plant top fresh weight and top dry weight were measured. Results showed that at

the recommended rate for all three plant growth regulators, there were no

significant difference in height or weight between the plant growth regulator-

treated groups of plants or the control group. The only observable difference noted

was in leaf coloration of the plants treated with plant growth regulators.

Wang (1999) investigated five WaveTM petunias, i.e., `Purple WaveTM', `Pink

WaveTM', `Misty Lilac WaveTM', and `Rose WaveTM', and two hedgaflora petunias,

i.e., `Dramatica CherryTM', and `Dramatica Hot PinkTM', to determine the effects of

plant growth regulators on plant size, branching, and flowering. Plant regulator

treatments consisted of daminozide (B-Nine) spray two times at 7500 ppm,

Paclobutrazol (Bonzi) spray two times at 30 ppm, paclobutrazol drench at 5 ppm,

paclobutrazol drench at 5 ppm plus spray at 30 ppm, and ethephone (Florel) spray

two times at 500 ppm. Plant diameter and central stem height were controlled

effectively through daminozide spray and paclobutrazol drench. Plant branching

was promoted by ethephone and daminozide. However, time to flowering was

delayed significantly in the ethephone treatment. The size of the first flower

responded to plant growth regulators negatively. The different responses to growth

regulators among different types of petunias and different varieties in the same

petunia type will be discussed based on the current trial and other separated

experiments.

Cerny et al. (1999) tested photo selective greenhouse covers that can filter out far-

red (FR) light and control plant height with minimal use of chemicals. The effects

of polymethyl methacylate (PMMA) filters containing FR-intercepting dyes were

evaluated on watermelon, pepper, chrysanthemum, and tomato to select an

optimum dye concentration. As the dye concentration increased, FR interception

increased, photosynthetic photon flux (PPF) decreased, and phytochrome

photoequilibrium increased from 0.72 to 0.82. Light transmitted through photo

selective filters reduced plant height effectively in all species tested. However,

watermelon was the most responsive (50% height reduction) and chrysanthemum

was the least responsive (20% height reduction) to filtered light. Tomato and

peppers had an intermediate response. In watermelons, total shoot dry weight was

reduced over 25% compared to the control plants, with a progressive decrease in

shoot weight as the dye concentration increased. The specific stem dry weight was

gradually reduced as the dye concentration increased. Specific leaf dry weight was

slightly reduced under filters, suggesting that smaller plants as opposed to a

reduction in dry matter production primarily caused total dry weight reduction.

Light transmitted through filters reduced percentage dry matter accumulation into

stems from 27% to 18% and increased dry matter accumulation into leaves from

73% to 82%. Photo selective filters are effective in controlling height similarly to

chemical growth regulators. Considering the PAR reduction by increase in dye

concentration, a dye concentration that gives a light reduction of 25% or 35% may

be optimum for commercial development of photo selective films.

Zheng et al. (1999) reported that plant architecture is a major consideration during

the commercial production of chrysanthemum (Dendranthema grandiflora

Tzvelev). They addressed this problem through a biotechnological approach:

genetic engineering of chrysanthemum cv. Iridon plants that ectopically expressed

a tobacco phytochrome B1 gene under the control of the CaMV 35S promoter. The

transgenic plants were shorter, greener in leaves, and had larger branch angles than

wild-type (WT) plants. Transgenic plants also phenocopied WT plants grown

under light condition depleted of far-red wavelengths. Furthermore, the reduction

of growth by the expressed PHY-B1 transgene did not directly involve gibberellins.

The commercial application of this biotechnology could provide an economic

alternative to the use of chemical growth regulators, and thus reduce the production

cost.

Bartel and Starman (2000) reported that Angelonia angustifolia `Blue Pacific',

Asteriscus maritimus `Compact Gold Coin', and Heliotropium aborescens

`Fragrant Delight' are three vegetatively propagated species of annuals. They

studied which plant growth regulator chemicals could be used to control height and

produce compact, well-branched, flowering plants. The plants arrived as rooted

plugs and were transplanted to 10 cm plastic containers. When the roots of the

transplanted plugs reached the edge of their containers, 15 days after transplanting,

the plant growth regulator chemicals were applied. Five different chemicals were

used in spray applications at two rates measured in mg L-1: ancymidol at 66 and

132; daminozide at 2500 and 5000; paclobutrazol at 20 and 40; ethephon at 500

and1000; and uniconazole at 10 and 20. One drench application of uniconazole at 1

and 2 mg L-1 and one control (water spray) were also used. Total plant height, plant

width, flower number, node number, stem length, internode length, and numbers of

days to visible bud were recorded. Ancymidol at both rates caused stunting and

flower distortion in asteriscus; however, it was not effective on angelonia or

heliotrope. Paclobutrazol and uniconazole sprays were ineffective in controlling

height on all three species. Ethephon at both rates was effective in controlling

height, and producing well-branched plants in all three species, yet it caused a

delay in flowering. Uniconazole drench at both rates was also effective in

controlling height but caused stunting. In general, daminozide at 5000 mg L-1 was

most effective in controlling foliage height without a delay in flowering or decrease

in flower size or number in all three species.

Wulster and Ombrello (2000) reported hat growth and flowering of Ixia hybrids as

potted plants can be controlled environmentally by cool pre plant storage of corms,

regulation of greenhouse forcing temperatures, and application of a growth

retardant. Paclobutrazol applied as a pre plant corm soak, a postemergent drench,

or a postemergent spray in combination with a 2- to 4-week pre plant storage of

corms at 7°C, and an 18°C day/10°C night forcing temperature produced attractive

and marketable plants.

Gianfagna et al. (2000) studied Aquilegia cultivars `Songbird Bluebird', `Songbird

Robin', `Dove Improved', `Colorado Violet/White' and five cultivars from new

experimental genetic lines (`Red and White', `Rose and White #1', `Rose and White

#2', `Scarlet and Yellow' and `White'). Plants were started from seed on 5 Jan.

1999 and grown in either natural light or 33% shade, and treated with gibberellins

(GA4/7) at the seven-leaf stage. Flowering time, number of flowers per plant, and

plant height were evaluated. All five cultivars from the new genetic lines bloomed

during the study. `White', grown in shade and treated with GA4/7, bloomed 2 weeks

earlier (115 days) than untreated plants grown in natural light (130 days).

`Songbird Robin', treated with GA4/7, bloomed in 146 days, and was the only other

cultivar to bloom. Flower numbers were greater in natural light than in 33% shade.

GA4/7 increased flowering for four of five cultivars, in the new genetic lines, grown

in natural light. In shade, GA4/7 increased flowering for three of five cultivars.

Height response to GA4/7 was significant in both natural light and 33% shade. Four

of the five cultivars in the new genetic lines were taller when treated. All five of

these cultivars were taller when grown in natural light verses 33% shade. `White'

and both `Rose and White' cultivars were consistently taller, bloomed earlier and

were more floriferous when treated with GA4/7.

Gibson and Whipker (2000a) treated ornamental cabbage and kale (Brassica

oleracea var. acephala L.) plants of cultivars Òsaka White' and `Nagoya Red' with

paclobutrazol and uniconazole as foliar sprays or soil drenches. These treatments

were compared to the industry standard of daminozide foliar sprays. Ten plant

growth regulator (PGR) drench treatments (in mg a.i. per pot) were applied 22 days

after potting: paclobutrazol at 1 to 16 and uniconazole at 0.125 to 2. Thirteen PGR

foliar sprays (in mg L-1) were also applied: paclobutrazol at 5 to 80, uniconazole at

2 to 32, daminozide at 2500, 2500 (twice, with the second application occurring 14

days later), or 5000, and an untreated control. Applying drenches of paclobutrazol

at 4 mg or uniconazole at 0.5 mg controlled height by 16 to 25%, but at the cost of

$0.11 per pot would not be economically feasible for growers to use. Paclobutrazol

foliar sprays at concentrations of up to 80 mg L-1 were ineffective in controlling

plant height and diameter of either Òsaka White' or `Nagoya Red'. Uniconazole

foliar sprays between 2 and 8 mg/L were effective in controlling height (by 19%)

and diameter (by 15%) as daminozide foliar sprays of 2500 mg L-1, sprayed twice,

with a cost to the grower of $0.02 per pot.

Gibson and Whipker (2000b) transplanted 26 ornamental cabbage and kale

(Brassica oleracea var. acephala L.) cultivars into 20.8 cm (8 inch) pots to classify

their foliage traits and determine their response to the plant growth regulator (PGR)

daminozide. Daminozide foliar sprays were applied at 0, 2500, or 5000 mg L–1

(ppm) 3 weeks after potting. Two cultivars treated with 2500 mg L-1 and eight

cultivars treated with 5000 mg L–1 were significantly smaller in height when

compared to the non-treated plants. Using the Range/LSD formula, the vigour of

the cultivars was classified by height. Foliage characteristics were described and

cultivars of ornamental cabbage, notched ornamental kale, and curly ornamental

kale were selected based on the shortest number of days until a significant centre

colour change and the largest centre colour diameter. In second experiment,

recommended cultivars selected in first experiment were treated with daminozide

at 5000 mg L–1 or uniconazole at 5 mg L–1 14 days after potting, plus a non-treated

control. All cultivars responded similarly to the PGRs with greater control being

observed with daminozide with a smaller plant height of 13% as compared to 6%

for uniconazole. For effective height control, PGR applications to ornamental

cabbage and kale should be applied 2 weeks after potting.

Neily et al. (2000) determined the effects of treatment with gibberellic acid (GA)

on changes in diurnal growth rhythms caused by maturation and day/night

temperature differential (DIF) in zinnia (Zinnia elegans Jacq. `Pompon'). Plants

were treated with GA3 or with the GA biosynthesis inhibitor daminozide under

three DIF regimes (+5 DIF: 21°C DT/16°C NT; 0 DIF: 18.7°C constant; –5 DIF:

16.5°C DT/21.5 C NT), each with a daily average temperature of 18.7°C, at two

developmental stages: stage 1, the period of vegetative growth before flower bud

formation; and stage 3, growth just before anthesis. Instantaneous stem elongation

rates (SER) were measured using linear voltage displacement transducers. The DIF

regime, as has been previously shown, influenced stem elongation primarily by

altering the size of an early morning peak in SER; peak height increased as DIF

became more positive. GA3 increased SER throughout the diurnal period with a

proportionately larger effect on nighttime growth. Conversely, daminozide

decreased SER more or less equally throughout the diurnal period. Neither GA3 or

daminozide transformed growth patterns to match those of positive or negative DIF

plants, but instead simply increased or decreased growth amplitude. Furthermore,

neither growth regulator altered the basic diurnal SER pattern at any DIF, or

influenced the observed shift to greater nighttime growth as plants matured from

stage 1 to stage 3. The results suggest that neither the effects of DIF, nor the age-

related shift in diurnal growth distribution can be explained by changes in total

availability of GA in the plant.

Li et al. (2000) conducted experiment to determine if covering at the end of the day

(EOD) with photo selective films was effective in controlling height of vegetable

seedlings. This will allow growers to maintain a high light level during daytime for

optimum growth of plants. Cucumber seedlings were exposed to light transmitted

through a photo selective film and a clear control film. Three exposure durations:

continuous, exposure to filtered light from 3:00 pm to 9:00 am, and from 5:00 pm -

9:00 am, was evaluated. Results show that, after 15 days of treatment, about 25%

of height reduction could be achieved by exposing the plants at the EOD from 3:00

pm to 9:00 am or from 5:00 pm to 9:00 am. Plants grown continuously under

filtered light were the shortest. Compared to plants grown in photo selective

chamber continuously, EOD exposed plants had greater leaf, stem and shoot dry

weights, greater leaf area and thicker stem. Specific leaf and stem dry weights were

also greater in EOD exposed plants. Number of leaves was not significantly

affected by any exposure periods tested. The results suggested that the EOD use of

photo selective film is effective in reducing height of cucumber seedlings. The

responses of other crops need to be evaluated to test the feasibility of using photo

selective film as a EOD cover on wide range of crops.

Takaichi et al. (2000) raised muskmelon (cv. Erles Knight Natsu No. 2), tomato

(cv. Kyouryoku-Beiju No. 2) and cucumber (cv. Resnei) seedlings to clarify the

effect of red/far-red photon flux ratio (R/FR) of solar radiation on growth. R/FR

ratio was altered using different covering materials. The effects of light treatments

on plant height became apparent after a few days. The high R/FR treatment

inhibited stem and petiole elongation but the low one promoted them. The effect of

changing R/FR was larger in muskmelon seedlings than in tomato seedlings. Leaf

emergence and size were almost the same among the treatments. Although stem

and petiole lengths of the seedlings differed at the end of treatment, no differences

were seen in subsequent stem growth, flowering and fruiting after transplanting

into normal conditions. The effects of changing R/FR occurred with small time

lags and had no residual effects. Dry matter production was usually reduced by

covering with coloured materials. For cucumber seedlings, the effects of short term

covering with the films in daytime on stem elongation were investigated. Degree of

stem elongation was approximately proportional to estimated mean R/FR during

daytime in the R/FR range 0.8-2. Differences due to treatment period were not

apparent. These characteristics are convenient for plant height control because no

strict adjustment of the light environment is required. Changing R/FR of solar

radiation by covering could be applied to control shoot morphology of vegetable

seedlings.

Kuehny et al. (2001) transplanted plugs into jumbo six packs and sprayed with a

solution of chlormequat/daminozide with concentrations of 1000/800, 1250/1250,

or 1500/5000 mg L-1 when new growth was 5 cm in height or width. Three

different species were grown in the fall (Dianthus chinensis L., `Telstar Mix',

Petunia × hybrida Hort. Vilm.-Andr., `Dreams Red', and Viola × wittrockiana

Gams., `Bingo Blue'), winter [Antirrhinum majus L., `Tahiti Mix', Matthiola

incana (L.) R. Br., `Midget Red', and P. × hybrida, `Dreams Mix'], and spring

[Catharanthus roseus (L.) G. Don, `Cooler Pink', Salvia splendens F. Sellow ex

Roem. & Schult., Èmpire Red', and Begonia × semperflorens-cultorum Hort.,

`Cocktail Mix']. The treatments significantly reduced finished plant size of all

species for each season. There was a significant difference in finish size between

sources for Dianthus, Antirrhinum, Matthiola, Catharanthus, Salvia, and Begonia.

The efficacy of chlormequat/daminozide also differed for each source of Dianthus,

Matthiola, and Begonia, but the treatments minimized the differences in finish size

between sources for Petunia and Viola.

Pasian and Bennett (2001) reported that seeds of `Bonanza Gold' marigold

(Tagetes patula L.), `Cherry Orbit' geranium (Pelargonium hortorum L.H. Bailey),

and `Sun 6108' tomato (Lycopersicon esculentum Mill.) were soaked for 6, 16, or

24 hours in paclobutrazol solutions of 0, 500, or 1000 mg L-1. After the soak

treatment, seeds were dried for 24 hours prior to laboratory germination testing or

sowing in plug trays. Percentage of emergence and seedling height were measured

16, 26, and 36 days after sowing. Laboratory germination of treated seeds was less

than that of the control, which was attributed to the PGR being concentrated around

the seed on the blotters. In contrast, seedling survival was unaffected in plugs. The

higher concentration of PGR and longer times of soaking increased growth

regulation, but also inhibited emergence of geraniums (71% vs. 99%). When seeds

were imbibed 6, 16, or 24 hours, growth restriction was 31%, 31%, and 40%,

respectively, for tomato, 61%, 37%, and 76%, respectively, for geranium and 30%,

38%, and 41%, respectively, for marigold. These results indicate that PGR

application to geranium, marigold, and tomato seeds may be feasible using a 6- or

16-hour soak in 500 mg L-1 paclobutrazol.

Rajapakse et al. (2001) reported recent developments in light manipulation as a

non-chemical alternative to chemical plant height control of greenhouse crops. Far-

red (FR) light absorbing films were effective in reducing height of a wide range of

plants, the magnitude varying with species. A dye concentration that gives a light

reduction of 25% was found to be suitable for commercial films because films with

higher dye concentrations reduced the transmission of photosynthetic photon flux

(PPF) but did not result in further height reduction. Among crops tested,

watermelon and cucumber seedlings showed more height reduction than bell

pepper (Capsicum annuum) and tomato seedlings and chrysanthemums

(Dendranthema grandiflorum). Photo selective films affected the flower

development of some crops. Flowering of long day plants (petunia and

snapdragon) was delayed by 7 to 13 days under the FR light absorbing film. The

films did not affect flowering of miniature roses (day neutral plant),

chrysanthemum, zinnia, or cosmos (short day plants). In nature, proportion of FR

light increases during early evening. End of the day (EOD) exposure to photo

selective films allows growers to make use of high light during the day and

exclude elongation-stimulating FR light in the evening. A significant height

reduction (25%) could be achieved by EOD exposure to FR light absorbing films

(compared to 44% height reduction by continuous exposure). EOD exposed plants

had more dry weight than the plant exposed continuously to FR light absorbing

films. Depending on height reduction desired, EOD exposure may be solely

effective.

Runkle and Heins (2002) developed photoselective plastic filters that reduce the

transmission of far-red light (FR, 700-800 nm) to potentially reduce stem extension

and thus plant height. However, an FR-deficient (FRd) environment can also delay

flowering, particularly in long-day plants (LDP). Our objective was to determine if

seedlings could be grown under an FRd environment to reduce extension growth

without subsequently delaying flowering upon removal from filter treatments.

Pansy (Viola × wittrockiana Gams.), petunia (Petunia × hybrida Vilm.-Andr.),

impatiens (Impatiens walleriana Hook.), snapdragon (Antirrhinum majus L.) and

tomato [Solanum lycopersicon L. (syn.: Lycopersicon esculentum)] were placed

under the FR-intercepting (FR-i) filter or a neutral density (N) filter that

transmitted a similar photosynthetic daily light integral. A third treatment consisted

of transferring plants from the N to the FR-i filter when leaves of each species

began to touch (after 18 or 24 days under the N filter). After 25-35 treatment days

with a 16-hour photoperiod at 20 °C, seedlings were measured and then grown

under natural photoperiods (>14.5 h) at 20 °C in a glass greenhouse with no filter

treatments until flowering. Compared with that of seedlings continually under the

N filter, stem or petiole length in the FRd environment was significantly reduced in

impatiens (by 10%), pansy (by 18%), petunia (by 34%), snapdragon (by 5%), and

tomato (by 24%). Extension growth in plants held continually under the FR-i filter

was similar to that of plants transferred from the N to the FR-i filter when leaves

first touched. Flowering of plants from plugs in the FRd environment was delayed

by 2-3 days in snapdragon, petunia, and pansy. At flowering, flower number and

plant height of all species were similar among treatments. Therefore, the FR-i filter

presents an attractive method of controlling seedling height with minimal impact

on flowering when plants are subsequently removed from filter treatments.

Fukuda et al. (2002) studied the effect of light quality on the growth of petunia

(Petunia × hybrida Vilm.) 'Baccarat Blue Picotee', which were grown in growth

chambers under a metal halide (MH), high pressure sodium (HPS) and blue (B)

lamps, at different light intensities and duration, additionally, these were sprayed

with GA3 and uniconazol, a growth retardant. Plant shapes were more compact

under HPS than under MH or B. The longest lateral shoot under HPS was about

30% shorter than that of plants grown under MH or B. The average internode

length was also shorter under HPS than the others; this result is attributed to the

high-red:far-red light ratio (R/FR) of HPS, which was mediated by plant

phytochromes. Light intensities also influenced plant height, which increased with

decreasing light intensity under MH and HPS. Furthermore, plant height under

HPS was shorter than those under MH in all light intensities. The rate of shoot

elongation was reduced when the plants were transferred from MH to HPS. The

final light quality determined the plant height. But, it had no residual effect. The

growth inhibition by HPS was reversible by the application of GA3. Whereas,

uniconazol had no effect on stems exposed to HPS. These results suggest that the

high R/FR ratio of HPS inhibits GA synthesis and, therefore plant height was

shorter than plant exposed to which has a lower R/FR ratio.

Gibson and Whipker (2003) reported that vigorous Osteospermum (Osteospermum

ecklonis) cultivars Congo and Wildside received foliar sprays of daminozide or

daminozide+chlormequat (Expt. 1). Both cultivars responded similarly to the plant

growth regulator (PGR) treatments. Only a limited amount of plant height control

occurred using 5 000 mg L-1 (ppm) daminozide+1 500 mg L-1 chlormequat or 5

000 mg L-1 daminozide+3 000 mg L-1 chlormequat. Flowering was delayed,

phytotoxicity was observed, while peduncle length increased, suggesting that

higher concentrations of daminozide or chlormequat may or not be effective at any

concentration and may result in increased phytotoxicity. In Expt. 2, 'Lusaka'

received foliar sprays or substrate drenches of paclobutrazol or uniconazole. Foliar

sprays <less or =>80 mg L-1 paclobutrazol or <less or =>24 mg L-1 uniconazole

were ineffective in controlling plant growth. Substrate drenches of paclobutrazol

(a.i.) at 8 to 16 mg per pot (28 350 mg=1.0 oz) produced compact plants, but at a

cost of $0.23 and $0.46/pot, respectively, would not be economically feasible for

wholesale producers to use. Uniconazole drenches were effective in producing

compact 'Lusaka' osteospermum plants. Uniconazole drench concentrations of

0.125 to 0.25 mg/pot were recommended for retail growers, while wholesale

growers that desire more compact plants should apply a 0.25 to 0.5 mg per pot

drench. Applying uniconazole would cost $0.06 for a 0.25 mg drench or $0.12 for

a 0.5 mg drench.

Gibson et al. (2003) investigated the efficacy of pinching, daminozide,

flurprimidol, uniconazole, or paclobutrazol + daminozide tank mix for plant height

control, diameter control, and days to anthesis on Argyranthemum frutescens cv.

Comet Pink. Plants were pinched 14 days after transplanting or treated 23 days

after transplanting with foliar sprays of five concentrations (mg/litre) from each

plant growth regulator (daminozide at 2500, 2500 (applied twice), 5000, 7500 or

10 000; paclobutrazol at 20, 40, 80, 120 or 160 mixed with daminozide at 1250;

uniconazole at 5, 10, 20, 40 or 80; and flurprimidol at 25, 50, 75, 100 or 125).

Pinching reduced the plant height, but delayed the anthesis compared to the

control. Plant diameter was unaffected by pinching. None of the plant growth

regulators affected the time to anthesis. Daminozide was ineffective in controlling

plant height, and plant diameter increased with 2500, 2500 (applied twice), and

5000 mg L-1. Flurprimidol was effective at 50-125 mg/litre for height control and

at 125 mg L-1 for diameter control. However, phytotoxicity was observed at 100-

125 mg L-1. Uniconazole was effective at 40 and 80 mg L-1 with phytotoxicity

evident at 80 mg/litre. The paclobutrazol + daminozide tank mix did not affect

plant height, but plants treated with 20 or 40 mg paclobutrazol L-1 + 1250 mg

daminozide L-1 had larger diameters than the control plants. Flurprimidol at 50-75

mg L-1 or uniconazole at 40 mg L-1 were the most effective plant growth regulators

for Comet Pink.

Carvalho and Heuvelink (2003) investigated the influence of assimilate availability

on the number of flowers per plant, individual flower size and plant height of

chrysanthemum in different seasons, integrating the results from eight greenhouse

experiments. Increased assimilate availability was obtained by higher light

intensity, higher CO2 concentration, lower plant density or longer duration of the

long-day (LD) period. Within each experiment, conditions that were expected to

increase assimilate availability indeed resulted in higher total drymass of the plant,

excluding roots (TDMp). In contrast, flower mass ratio was hardly affected, except

for the increased duration of the LD period that significantly reduced the

partitioning towards the flowers. Consequently, an increase in total flower drymass

with assimilate availability was observed and this was mainly a result of higher

numbers of flowers per plant, including flower buds (NoF). Individual flower size

was only influenced by assimilate availability when average daily incident PAR

during short-day period was lower than 7.5 mol m-2 d-1, resulting in lighter and

smaller flowers. Excluding the positive linear effect of the duration of the LD

period, assimilate availability hardly influenced plant height (<10% increase). It is

concluded that within a wide range of growth conditions chrysanthemum invests

additional assimilates, diverted to the generative organs, in increasing NoF rather

than in increasing flower size. Irrespective of the growth conditions and season a

positive linear relationship (r2=0.90) between NoF and TDMp was observed. This

relationship was cultivar-specific.

McDonald and Arnold (2004) determined the affects of paclobutrazol and

ancymidol on production and landscape performance of ornamental cabbage

(Brassica oleracea L. var. acephala A.P. deCandolle `Dynasty Pink'), calendula

(Calendula officinalis L. `Bon Bon Orange'), and pansy. Seeds were germinated in

plug trays (1.5 cm3 inverted cone-shaped pockets) in a growth chamber with a 12 h

photoperiod at 25/21°C day/night. Plants were sprayed with paclobutrazol

(formaulated as Bonzi) or ancymidol (formulated as Arest) at plug stage (cabbage,

pansy, and calendula on 25 Sept., 2 Oct., 11 Nov., respectively), at 14 days after

transplant into 0.73 L containers, or at both stages. Paclobutrazol was applied at 0,

5, 10 or 15 mg·L-1 and ancymidol at 0, 2, 4, or 8 mg L-1. Cabbage (30 Oct.), pansy

(6 Nov.), and calendula (4 Dec.) were transplanted to landscape beds to assess

residual effects on growth and flowering. Cabbage and calendula, showed minor

differences in growth during greenhouse production due to varying rates of either

paclobutrazol or ancymidol, but exhibited a greater response to application time.

Only minor differences in growth occurred with pansy during greenhouse

production due to rate or time of application using ancymidol, but exhibited major

differences in response to both rate and time of application using paclobutrazol.

Maurya and Nagda (2004) planted uniform sized corms of gladiolus (Gladiolus

grandiflorus L. cv. Oscar) in last week of October at a distance of 30 cm between

rows and 20 cm between plants. The effect of GA (50, 100 ppm), Cycocel (500,

1000) and NAA (50, 100 ppm) on gladiolus plants. It was concluded that foliar

application of 100 ppm GA3 at 45 days after corm planting has shown superiority

in all vegetative, floral characters and corm & cormel yield viz., plant height

(128.53 cm), number of leaves (8.57) per plant, spike length (108.33 cm), spike

weight (128.87 g), number of florets (17.60) per spike, size of second florets (15.07

cm), number of spikes (1.67) per plant, size of largest corm (7.52 cm), number of

corms (1.80) per plant, number of cormels (11.53) per plant and weight of corms

(79.33 g) per plant. Whereas, a highest longevity of florets opening or survival on

spike (20.33 days) was recorded in 1000 ppm Cycocel.

Clifford et al. (2004) reported that a photo selective film was developed that

specifically reduces the transmission of far-red light [(FR), 700 to 800 nm],

offering an alternative strategy for height control. Two complementary trials, one

in the United Kingdom and one in the United States, showed that plants grown

under the FR film for 10 to 12 weeks were 20% shorter than control plants

growing under neutral density (ND) films transmitting a similar photosynthetic

photon flux as the FR film. In the United Kingdom trial, the FR filter delayed time

to 50% bract colour and first visible cyathia by 6.0 and 3.5 days, respectively, but

did not influence time to final harvest. In the United States trial, plants under the

FR film had an average of 25% more axillary branches than those under the ND

film. In addition, the effects of reduced red [(R), 600 to 700 nm] and blue [(B), 400

to 500 nm] light on internode length, plant biomass, and axillary branching were

determined using other photo selective plastics. Compared with plants under the

ND film, internode length was 9% or 71% greater in plants grown under

environments deficient in B or R, respectively. Our results indicate that poinsettia

is highly sensitive to the R: FR ratio and that spectral manipulation have potential

for height control of commercial poinsettia crops.

Blom et al. (2004) irrigated potted greenhouse-forced `Nellie White' Easter lilies

(Lilium longiflorum Thunb.) from emergence with water at 2, 5, 8, 11, or 15°C

either onto the shoot apex (overhead) or onto the substrate for a 0, 2, 4, 6-, 8, 10, or

12-week period. Control treatment was at 18°C, either overhead or on substrate.

When irrigation water was applied overhead for the entire period between

emergence and flowering (12 weeks), plant height increased linearly with the

temperature of irrigation water (1.75 cm/°C). As the period of application with cold

water increased from 0 to 12 weeks, plant height decreased both in a linear and a

quadratic manner. Forcing time was negatively correlated with height with the

shortest plants delayed by 3 to 6 days. Water temperature did not affect bud

abortion or the number of yellow leaves. Irrigation water temperature had no effect

on plant parameters when applied directly on the substrate.

Pak et al. (2005) tested efficacy of application methods and concentration of plant

growth retardants on growth of chrysanthemum (Dendranthema × grandiflorum

cv. Cheasepeake). B-9 or cycocel (CCC) as a growth retardant was applied as

drench or sub-application with nutrient solution. In the case of B-9 drench

treatments, as B-9 concentrations increased, numbers of flowers and flower buds

increased except in the 1500-ppm treatment. Increasing concentration of CCC also

resulted in reduction of flower numbers, total plant height, total leaf area, branch

number, and fresh weight. Reduction ratio of total plant height in 2000 ppm

showed about 56.9% being compared to that of the 100-ppm drench treatment. B-9

or CCC, combined with nutrient solution, was also supplied from the C-channel

sub-irrigation system. The B-9 sub-application treatment showed no significance

among these concentrations, but flower numbers, total plant height, average plant

height, and leaf numbers decreased as concentrations of CCC increased. B-9 or

CCC with the same concentration was drenched after 2 weeks of the first

experiment to compare planting time efficacy. Measured data increased until B-9

increased up to 2500 ppm and severe growth retardation resulted from the 5000

ppm treatment. Through this growth retardant application study, the combination of

drenching concentration and period of plant growth regulators (PGRs) may result in

effective growth retardation and reduction of application concentrations for pot

plant production.

Keever and Kessler (2005) studied how to control plant height of Coreopsis

grandiflora Èarly Sunrise' (ES) and Rudbeckia fulgida `Goldsturm' (RG) grown

under NIL with plant growth retardants (PGR) without offsetting earlier flowering

promoted by NIL. Treatments under NIL were three rates of daminozide,

daminozide plus chloromequat, flurprimidol, uniconazole, and NIL and natural

controls. Plant height was reduced 3% to 38% in ES and 8% to 31% in RG and

time to visible bud was unchanged by all PGR treatments compared to the NIL

control. Time to visible bud was unchanged in RG by all PGR treatments and

flurprimidol in ES, but the remaining PGR treatments increased time to visible bud

compared to the NIL control in ES. Only ES plants treated with daminozide and

daminozide plus chloromequat at the two highest rates and all rates of uniconazole

were similar in height to the natural control. RG plant heights with the two highest

rates of flurprimidol and uniconazole and the highest rate of daminozide plus

chloromequat were less than the natural control; heights of plants in the remaining

PGR treatments were similar to the natural control. Quality rating was unchanged

in RG but was increased in ES by all PGR treatments compared to the NIL control.

Ilias and Rajapakse (2005) conducted experiment to see if brief exposure to end-of-

the-day (EOD) red (R) or far red (FR) light can overcome the flowering delay of

petunia (Petunia × hybrida Vilm.-Andr. `Countdown Burgundy') grown under FR

deficient greenhouse environments with no adverse effects on stem elongation.

Plants were grown under clear, FR, and R light absorbing greenhouse films

(control, AFR, and AR films, respectively) and exposed to R or FR light at the end of

the photoperiod for 15 minutes. At flowering, main stem of plants grown under the

AR film was about 17% longer and that of AFR film grown plants (without EOD

treatment) was about 50% shorter than control plants. EOD-R light reduced stem

elongation of control plants but had no effect on AFR or AR film-grown plants.

EOD-FR light increased stem elongation in plants grown under AR and AFR films

but the percentage increase was greater under AFR film (7%, 19%, and 64%

increase in control, AR, and AFR films, respectively). However, plants that received

EOD-FR light under AFR film were 25% shorter than control plants that received

no EOD light. AFR film delayed flowering by 11 days but AR film had no effect.

Fifteen-minute exposure to EOD-R or -FR light had no effect on flowering under

control and AFR film. Although the exposure to brief EOD-FR partially increased

stem elongation, it was not sufficient to accelerate flowering. Treatments to

enhance flowering can cause stem elongation. Therefore, care should be taken to

avoid improper crop timing, especially with long-day plants.

Karlsson and Werner (2005) identified flowering in response to day length for

sunflower (Helianthus annuus L. `Pacino Gold'). Germination and seedling

development occurred at 20°C and long days (LD, 16 hours) following direct

seeding into 10 cm pots. Sixteen days after seeding, plants were placed at LD or

short days (SD, 8 hours), 20°C and 8 mol d-1 m-2. Flowering was recorded at the

stage of reflexed petals after 48 SD. At the time of flowering in SD, flower buds

were of minute size under LD. Plants started at LD, and moved to SD after 1, 2, or

3 weeks, flowered at similar times as those grown under uninterrupted SD

conditions. Four initial weeks of LD delayed flower development with 7 days,

compared to a continuous SD environment. On the other hand, 2 to 3 weeks of

initial SD followed by LD hastened flowering with 5 to 10 days. With increasing

number of early LD from 1 to 4 weeks, plant height at flowering doubled from 20

to 40 cm. Average plant height in continuous SD was 18 cm. Plants grown

exclusively or moved to LD after 1 to 4 weeks of SD were similar in height to

plants finished at SD with 4 initial weeks of LD. Combinations of SD and LD may

be used to manage height and rate of development in the sunflower `Pacino Gold'.

Pinto et al. (2005) stated that zinnias have good potential to be used as flowering,

potted plants, being a quick source of novelty for the floriculture industry with the

aid of growth retardants. This study evaluated the effect of growth retardants on

development and production of short, compact and attractive plants of potted

'Lilliput' Zinnia elegans, a highly ornamental zinnia with low cost seeds. Trials

were set up in randomized blocks, with ten treatments (control and three treatments

of each retardant: daminozide, paclobutrazol and chlormequat) and four

replications (two pots per experimental unit, with one plant per 0.6-L pot).

Paclobutrazol (0.5, 0.75 and 1.0 mg a.i. per pot) and chlormequat (1.0, 2.0 and 3.0

g L-1) were applied as a single drench (40 mL per pot), and daminozide (2.5, 3.75

and 5.0 g L-1) as a single foliar spray to runoff (10 mL per pot), at apical flower

bud stage. Daminozide (2.5 and 3.75 g L-1), paclobutrazol (0.5, 0.75 and 1.0 mg

a.i. per pot) and chlormequat at 1.0 g L-1 significantly reduced plant height and side

branches length, without affecting flower diameter, delaying production cycle and

causing phytotoxicity symptoms. However, plants were not short and compact

enough to meet market quality demand. Chlormequat (2.0 and 3.0 g L-1) caused

phytotoxicity symptoms and daminozide (5.0 g L-1) delayed production cycle.

Runkle et al. (2006) determined the effectiveness of uniconazole when used as a

drench, eliminating the variability inherent in a spray application. Seedlings of

Celosia argentea L. var. plumosa L. `Fresh Look Red', Petunia × hybrida Vilm.-

Andr. `Prostrate Wave Rose', Salvia splendens Sell ex Roem. and Schult. `Vista

Red', and Tagetes erecta L. Ìnca II Gold' in 288-cell plug trays were transplanted 2

days after arrival into 10 cm pots filled with a soilless medium containing no bark.

Plants were placed in a greenhouse with a setpoint of 20°C and under a 16h

photoperiod provided by high-pressure sodium lamps. A single drench application

of 0, 0.04, 0.07, 0.15, or 0.30 mg active ingredient/pot was made 11 days after

transplant. The uniconazole drench inhibited internode elongation in these species

and higher rates provided a greater degree of response. At time of flowering, the

0.30 mg uniconazole drench inhibited shoot length in Celosia, Petunia, Salvia, and

Tagetes by 36%, 23% 26%, and 13%, respectively. Drenches of 0.04 or 0.07 mg

provided a desirable degree of height control for Celosia and Salvia. For vigorous

species like Petunia or Tagetes, 0.15 to 0.30 mg may be more appropriate. We

observed a 1- or 2-day delay in flowering of Salvia and Tagetes plants drenched

with 0.30 mg, but no delays in Petunia flowering.

Brigard et al. (2006) investigated the effects of 0, 250, 500, 750, or 1000 mg

paclobutrazol (PB)/L seed soak and soaking times from 1 to 12 hours on tomato

(Solanum lycopersicum L.) seed germination, seedling growth, and plant growth.

Adequate height control was obtained with 250 mg PB/L while soaking time did

not affect seedling growth. In a second experiment, PB was tested at 0, 50, 100,

150, 200, or 250 mg PB/L soaking the seed for 1 hour. A concentration of PB at

100 mg L–1 provided optimum control of hypocotyl elongation with minimal

residual effect on subsequent plant growth. In a third experiment, seed soaked at

the different PB concentrations were germinated and grown under light intensities

of 0.09, 50, 70, or 120 µmol m–2 s–1. Seedlings grown under 0.09 µmol m–2 s–1 were

not affected by PB treatment and did not develop an epicotyl. PB seed soak

treatment gave greater growth suppression under 50 µmol m-2 s-1 than under the

two higher light levels. Soaking tomato seeds in 100 mg PB/L for 1 hour prevented

early hypocotyl stretch of tomato seedlings with no long term effects on plant

growth. This treatment effectively prevented excessive hypocotyl elongation when

seeds were germinated under low PAR while not over controlling elongation under

high PAR conditions.

Magnitskiy et al. (2006) measured seedling emergence and shoot height of plugs as

affected by paclobutrazol application during seed soaking, priming, or coating on

seedling emergence and height. Verbena (Verbena × hybrida Voss. `Quartz

White'), pansy (Viola wittrockiana L. `Bingo Yellow Blotch'), and celosia (Celosia

cristata L. `New Look') seeds were soaked in water solutions of paclobutrazol and

subsequently dried on filter paper at 20°C for 24 h. Soaking seeds in paclobutrazol

solutions before sowing reduced growth and percentage seedling emergence of

verbena and pansy but had little effect on those of celosia. Verbena seeds soaked in

50, 200, or 500 mg paclobutrazol L-1 for 5, 45, or 180 min produced fewer and

shorter seedlings than controls. Osmopriming verbena seeds with 10 to 500 mg

paclobutrazol L-1 reduced seedling emergence. Seedling height and emergence

percentage of pansy decreased with increasing paclobutrazol concentrations from 2

to 30 mg L–1 and with soaking time from 1 to 5 min. The elongation of celosia

seedlings was reduced by soaking seeds in 10, 50, 200, or 500 mg paclobutrazol L-1

solutions for 5, 180, or 360 min. However, these reductions were negligible and

without any practical application.

Lund et al. (2007) investigated the effects of light quality [R:FR ratio of 0.4, 0.7,

and 2.4 (R = 600–700 nm, FR = 700–800 nm)] at the end of day were investigated

on potted chrysanthemums using growth chambers. After a 9-h photoperiod, the

30-min end-of-day lighting was provided by light-emitting diodes at low irradiance

by maintaining either red = 1 µmol m–2 s–1 (Rcon) or far-red = 1 µmol m–2 s–

1(FRcon). After 3 weeks of end-of-day lighting, plants given the lowest end-of-day

ratios (R:FR of 0.4 or 0.7) were taller than control plants (R:FR = 2.4). For low

ratios of R:FR (0.4), the actual intensities of R and FR did not affect plant height,

whereas for higher ratios of R:FR (0.7 and 2.4), plant height was greater for FRcon

than for Rcon. Leaf area of the lateral side shoots was lower for plants treated with

an R:FR of 0.4 compared with those of controls. Dry weight, stem diameter,

number of internodes, and number of lateral branches were unaffected by the end-

of-day ratio.

Lykas et al. (2008) investigated the possibility of using a photo selective

polyethylene greenhouse covering film as an alternative to chemical treatment for

production of compact potted gardenia (Gardenia jasminoides Ellis) plants. Two

types of experiments were carried out: 1) on gardenia cuttings rooted in rooting

benches; and 2) on young potted plants grown under low tunnels. In both

experiments, two types of cover materials were used: 1) a photo selective

polyethylene (P-PE), filtering light within the wavelength range 600 to 750 nm;

and 2) a common polyethylene film (C-PE) routinely used in greenhouse practice.

Values of photosynthetically active radiation (in a wavelength of 400 to 700 nm),

cover materials' spectral properties (in a wavelength range of 400 to 1100 nm), air

temperature, and relative humidity were recorded inside the rooting benches and

under the low tunnels. Plant growth parameters (main shoot length, lateral shoot

number, leaf area, and fresh and dry weight) were determined along the growth

cycle. Cuttings rooted under the P-PE film received light with high n values (ratio

of Rn: 655 to 665 nm to far red FRn: 725 to 735 nm) and high blue (B: 400 to 500

nm) to red (R: 600 to 700 nm) ratio (B:R) and were 68.7% shorter and had 21%

lower leaf area compared with cuttings rooted under the C-PE film. Similarly,

plants that were rooted and then grown under the low tunnels covered with the P-

PE film, compared with plants rooted and grown under C-PE film, were 59%

shorter, had 85% lower leaf area, 89% lower fresh weight, and 86% lower dry

weight, whereas they did not produce lateral shoots. However, plants rooted under

the C-PE film and then grown under the P-PE-covered low tunnels were 26%

shorter and developed fewer laterals than plants rooted and grown under tunnels

covered with C-PE film. Finally, plants rooted under the P-PE film and then grown

under tunnels covered with C-PE film developed into compact, well-shaped plants,

because they had a drastic reduction of height (56%) without an effect on leaf area,

shoot and leaf fresh and dry weight, and the number of lateral shoots.

CHAPTER 3

MATERIALS AND METHODS

3.1 Experimental location

All experiments were carried out at Agricultural Research Institute, Dera Ismail

Khan, Pakistan, during the years 2004-2007. Dera Ismail Khan (31º 49’ N to 70º 55’

E) is the extreme southern district of North West Frontier Province (NWFP) of

Pakistan. It has a total geographical area of about 1 million hectares of which only

0.308 million hectares are under cultivation (18.31% is under crops whereas

15.53% is not available for cultivation). Total irrigated area of Dera Ismail Khan is

about 14.73%. The climate is arid to semi-arid. It is hot and dry in summer with

moderate spells during monsoon season. The elevation ranges from 121 to 210

meter above sea level. The mean maximum temperature in summer and winter is

45 and 8oC, respectively. The mean annual precipitation ranges from 15-25 cm and

relative humidity varies from 51% in June to 78% in October.

3.2 Plant material and growing media

Seeds of Moss Rose (Portulaca grandiflora L.) cv. Sundance, Pansy (Viola

tricolour hortensis L.) cv. Baby Bingo, Snapdragon (Antirhinum majus L.) cv.

Coronette, Petunia (Petunia hybrida Juss.) cv. Dreams, Annual Verbena

(Verbena hybrida L.), Pot Marigold (Calendula officinalis L.) cv. Resina,

Annual Phlox (Phlox drummondii L.) cv. Astoria Magenta, Cornflower (Centaurea

cyanus L.) cv. Florence Blue, Oriental Poppy (Papaver orientale L.) cv. Burning

Heart, Flax (Linum usitatissimum L.) cv. Scarlet Flax, Zinnia (Zinnia elegans L.)

cv. Lilliput, Sunflower (Helianthus annuus L.) cv. Elf, French Marigold (Tagetes

Patula L.) cv. Orange Gate, African Marigold (Tagetes erecta L.) cv. Crush,

Cockscomb (Celosia cristata L.) cv. Bombay, Cosmos (Cosmos bipinnatus Cav.)

cv. Sonata Pink were obtained from Pride Seed Company, Lahore, Pakistan. Seeds

of these cultivars were sown into module trays containing leaf mould compost,

prepared locally at Agricultural Research Institute, Dera Ismail Khan, Pakistan.

Seed trays were kept at room temperature at night and they were moved out during

the day (08:00–16:00 h) under partially shaded area. After 70% seed germination,

plants were either directly transferred into the photoperiod chambers for reciprocal

transfer or potted into 9cm pots containing leaf mould compost and river sand (3:1

v/v) after 6 leaves emerged. This media was used for all experiments.

3.3 Plant nutrition and irrigation

Seedlings were normally irrigated with tap water (without any nutrients). After

potting, the plants were regularly watered and nutrients were applied manually

whenever required in the form of a soluble fertilizer, Premium Liquid Plant Food

and Fertilizer 8-8-8 (NPK) (Nelson Products Inc. USA).

3.4 Photoperiod controlled compartments

Plants of all cultivars were given equal and appropriate space on movable trolleys

in photoperiod chambers. They were remained outside the chambers for 8 h under

the ambient light conditions. At 1600 h each day, these plants were wheeled into

the photoperiod chambers where they were remained until 0800 h the following

morning. Day lengths extended inside each of the chamber by low irradiance

lighting (7 mol m-2 s-1, photosynthetic photon flux density i.e. PPFD) and was

measured with the light meter quantum sensor (LI-189, LI-COR Biosciences,

USA) obtained from National Agricultural Research Centre, Islamabad, Pakistan.

Two 60Watt tungsten light bulbs (Philips, Holland) and one 18Watt warm white

florescent long-life bulb (Philips, Holland) were fixed above 1 m high from the

trolleys. In all photoperiod chambers, the lamps were switched on automatically at

1600 h for a duration dependents on the day length required (8, 11, 14, 17 h and

11, 13, 15, 17 h). These chambers were continuously ventilated with the help of

micro exhaust fan (Fan-0051, SUPERMICRO USA) with an average air speed of

0.2 m.s-1 over the plants when inside the chambers, to minimize any temperature

increase due to heat from the lamps. Temperature and solar radiation were

measured in the weather station situated one kilometer away from the research

venue. Temperature was recorded with the help of Hygrothermograph (225-5020-

A Hi-Q Hygrothermograph, NovaLynx Corporation, USA) while solar radiation

was estimated using solarimeters (Casella Measurement, UK).

These photoperiod chambers were used in light intensity’s experiment except the

source of illumination. In this experiment SON-E Eliptical sodium lamps

(OSRAM, Germany) of 50 Watt (42µmol.m-2.s-1), 70 Watt (45µmol.m-2.s-1), 100

Watt (92µmol.m-2.s-1) and 150 Watt (119µmol.m-2.s-1) were used for 8 h duration.

3.5 Light measurements device

The light intensity measurements inside the photoperiod chambers were made

using a quantum sensor (LI-189, LI-COR Biosciences, USA) attached to a

Comarck 122 DC microvoltmeter. The readings obtained from this device were

expressed in μmol m-2 s-1 and represented as photosynthetic photon flux density

(PPFD). Whereas the solar radiation (photosynthetic active radiation, PAR) was

recorded using solarimeters installed in the weather station. This reading was

measured as MJ.m-2.d-1 and represented the total solar radiation (PAR).

3.6 Temperature measurements device

Temperature data during each experiment was recorded in the weather station, one

kilometer away from the research area using a hygrothermograph (225-5020-A Hi-

Q Hygrothermograph, NovaLynx Corporation, USA). It is a precision, self-

contained instrument that measures and records ambient temperature and relative

humidity simultaneously on a double scale chart. The hygrothermograph employs

an aged bimetal strip, which distorts with changes in temperature. This distortion is

magnified through a lever system, which moves a pen arm over the upper half of a

17.5 cm high chart. The response would be linear. Temperature is recorded over a

60 °C (110 °F) span. The span can be adjusted up or down to match the

temperature range of the installation site. Normal calibration adjustments were

made by turning a knurled knob, which moves the pen up or down the scale

through movements of the lever system.

A specially treated bundle of human hair is used to measure relative humidity over

the full range of 0-100%. The hair expands and contracts with increasing or

decreasing water vapour in the air. This movement is transmitted to the pen arm

using a linkage system. Opposing quadrants in the linkage linearize the nonlinear

response of the hair bundle. The chart was installed on a self-contained, battery-

operated clock. The drum rotation was 31 days. Large openings in the sides, end,

and bottom of the hygrothermograph case permit free flow of ambient air to the

sensors.

3.7 Plant growth substances

In plant height control experiment, A-Rest (Ancymidal), Bonzi (Paclobutrazol) and

Cycocel (Chlormequat chloride) plant growth regulators (PGRs) were used

(Supplied by: Chengdu Newson Biochemistry Co. Ltd., China). These growth

substances were obtained from National Agricultural Research Centre, Islamabad,

Pakistan.

To prepare a spray solution of A-Rest, Bonzi and Cycocel a standard laboratory

fume hood was used wearing protective hand and eyewear. A 30 mg a.i. of A-Rest

and Bonzi powder was dissolved in a 10 mL volume of ethanol and then diluted it

with 990 mL double distilled water (one-liter volume) to prepare a solution of 30

ppm (Lopes and Stack, 2003). Similarly, the spray solution of cycocel was

prepared by diluting 8.4 mL a.i. of cycocel into one-liter of double distilled water

(i.e. 1000 ppm) as described by Tol-Bert (1960) and Anonymous (2007a). These

PGRs were applied thoroughly on plant leaves and stems in order to obtained

maximum effect on plant height. First spray of PGRs was carried out after three

weeks of germination (at the emergence of 2-true leaves) whereas a second spray

of same concentration was applied after six weeks of germination.

3.8 Data collection

The following growth and developmental parameters were measured during the

course of the experiments.

3.8.1 Time to flowering

Flowering was defined as the anthesis of the first flower, from the raceme

(inflorescence), if any. Days to flowering were counted from the date of seed

sowing until the date of first flower opening (corolla fully opened). This was

recorded daily in all experiments.

3.8.2 Plant height

The height was measured from the point where the plant emerged from the

growing media to the top of the stem in centimetres.

3.9 Statistical procedures applied

To analyse the data, several statistical methods were used. All means and standard

errors were calculated using Microsoft Excel 2007. Standard errors of differences

between means were calculated using the MENU option in GenStat-8 (Lawes

Agricultural Trust, Rothamsted Experimental Station, U.K. and VSN International

Ltd. U.K.). Simple or multiple linear regression and non-linear regression

(FITNONLINEAR function, in reciprocal transfer experiments) were analysed

using GenStat-8. However, before analysing the non-linear data all values were put

in the model presented by Adam et al. (2003) and then the ‘Input Window’ was

submitted to the GenStat-8 for the analysis.

3.10 Ambient environmental data

3.10.1 Day length (hours per day)

0

2

4

6

8

10

12

14

16

18

Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep

Months of year 2004-2005

Day

len

gth

(h

.d-1

)

Fig 3.1 Day length (h.d-1) recorded from dawn to sunset at weather station.

3.10.2 Solar radiation / photosynthetic active radiation

6.00

6.50

7.00

7.50

8.00

8.50

9.00

9.50

10.00

10.50

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Months of year

PA

R (

MJ.

m-2

.d-1

)

2004200520062007

Winter Winter

S U M M E R

AutumSpring

Fig 3.2 Average photosynthetic active radiation (PAR, MJ.m-2.d-1) recorded using

solarimeters at weather station during the experimental year 2004-2007.

3.10.3 Monthly temperature (C)

0

5

10

15

20

25

30

35

40

45


Months of year 2004

Tem

per

atu

re (

°C)

MaximumMinimumAverage

0

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10

15

20

25

30

35

40

45


Months of year 2005

Tem

per

atu

re (

°C)


Fig 3.3 Monthly maximum, minimum and average temperature (C) recorded

using a hygrothermograph at weather station during the experimental year 2004-

2005.

0

5

10

15

20

25

30

35

40

45


Months of year 2006

Tem

per

atu

re (

°C)


0

5

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15

20

25

30

35

40

45


Months of year 2007

Tem

per

atu

re (

°C)


Fig 3.4 Monthly maximum, minimum and average temperature (C) recorded

using a hygrothermograph at weather station during the experimental year 2006-

2007.

0

5

10

15

20

25

30

35

40


Months of year

Ave

rage

tem

per

atu

re (

°C)

2004200520062007

Fig 3.5 A cumulative graph showing an average monthly temperature (C) during

the experimental year 2004-2007.

CHAPTER 4

RESULTS AND DISCUSSION

4.1 Effects of different sowing dates (ambient day length) on time to flowering of important ornamental annuals

4.1.1 Introduction

Day length refers to the temporal length of a day, or 24 h, during which there is

daylight. Due to the diffusion and refraction of sunlight by the atmosphere, there is

actually daylight even when the sun is slightly below the horizon. Day length can

be computed from the moment the upper limb of the sun's disk appears on the

horizon during sunrise to the moment when the upper limb disappears at the

horizon during sunset.

Day length is critical to the growth and lifecycle of many plants. Growers of

ornamental annuals often supplement natural light to take a plant into a different

time of the year. Seeds need to be planted at the right time. If seeds are sown too

early, bad weather will destroy the crop. If sown late, it will not have sufficient

time to mature. Many plants use the length of the day to judge when to flower.

Different cultivars of plants react to day length in different ways. The plant uses

the energy from sunlight to power its growth. Temperature, nutrient levels in the

soil and water are all important but without sunlight plants will not grow. The more

sunlight, the more energy is available for the plant. Similarly, the longer a day

lasts, the more time is for earth to absorb energy from the sun. Thus, longer days

typically result in warmer days, while shorter days result in cooler days (Thomas

and Vince-Prue, 1997).

Flowering of ornamental plants is not only important for their continued

propagation but also for displaying the plant at its most attractive point of sale.

Flower development of many ornamental annuals is harmonized during the season

by using changes in day and night length, which indicates that the flowering

response is photoperiodic (Garner and Allard, 1920). Broadly, flowering plants can

be classified as long day plants (LDPs), short day plants (SDPs), or day neutral

plants (DNPs). LDPs are plants that flower when the day is longer than a critical

length (i.e. the night is shorter than a critical length). These plants generally flower

in the spring or early summer, as days are getting longer. SDPs are plants that

flower when the day is shorter than a critical length, or the night is longer than a

critical length. These plants generally flower in late summer or fall, as days get

shorter (Thomas and Vince-Prue, 1997).

The knowledge of plant response to different day length facilitates gardeners to

grow them year round and maintain their constant supply in the market. In recent

years, the importance of ornamental plants scheduling has greatly increased

particularly in countries, which are earning sufficient foreign exchange through

ornamental export. This increased emphasis on scheduling is focused primarily on

mass demands of the market for consistency in product and presence of flowers at

sale time. Vernieri et al. (2003) reported that time of flowering reduced

significantly when sunflower was sown early. Plant growth and development is

also affected by early or late sowing time (Justes et al., 2002; Balkaya et al., 2004;

Karaguzel et al., 2005; Sundeep et al., 2005; Wang et al., 2006).

As annual ornamental plants provide a display for a limited period therefore there

is relatively short market season for these crops. If the crop is matured early or late,

it will be wasted. Therefore, there is an intense need to understand how plant

induce flowering when the day length is increased or decreased to regulate the

supply of these flowering crops to the market (Pearson et al., 1994) which would

be most beneficial for the growers involved in this business. Keeping in view the

importance of plant scheduling, an experiment was designed to examine an applied

possibility of plant scheduling of various ornamental annuals by sowing them at

different dates.

4.1.2 Materials and Methods

Present experiment was conducted at Agricultural Research Institute, Dera Ismail

Khan, Pakistan, during the year 2004-2005 and 2005-2006. Seeds of SDPs such as

Zinnia cv. Lilliput, Sunflower cv. Elf, French Marigold cv. Orange Gate, African

Marigold cv. Crush, Cockscomb cv. Bombay, Cosmos cv. Sonata Pink were sown

from 1st of September to 15th of January 2004 and 2005 at 15 days interval.

Similarly, seeds of LDPs such as Moss Rose cv. Sundance, Pansy cv. Baby Bingo,

Snapdragon cv. Coronette, Petunia cv. Dreams, Annual Verbena cv. Obsession,

Pot Marigold cv. Resina, Annual Phlox cv. Astoria Magenta, Cornflower cv.

Florence Blue, Oriental Poppy cv. Burning Heart and Flax cv. Scarlet Flax were

sown from 1st of March to 15th of July 2005 and 2006 at 15 days interval. The

reason of planting SDPs between September and January (short day length) and

LDPs between March and July (long day length) was to estimate flowering

character under their respective responsive environment (Table 4.1.1 and 4.1.2).

Seeds of all cultivars were sown into module trays containing locally prepared leaf

mould compost.



six plants of each cultivar were shifted to the experimental area where they were

potted into 9cm pots containing leaf mould compost and river sand (3:1 v/v) after 6

leaves emerged.

Plants were irrigated by hand and a nutrient solution [(Premium Liquid Plant Food

and Fertilizer (NPK: 8-8-8); Nelson Products Inc. USA)] was applied twice a

week. Plants in each treatment were observed daily until flower opening (corolla

fully opened). Numbers of days to flowering from emergence were recorded at

harvest and the data were analysed using GenStat-8 (Lawes Agricultural Trust,

Rothamsted Experimental Station, U.K. and VSN International Ltd. U.K.).

Table 4.1.1 Environmental detail of experiment 4.1 (2004-2005).

Growing Season Diurnal temperature (°C) Ambient

day length (h.d-1)

Daily light integral

(MJ.m-2.d-1) Maximum Minimum Average

Zinnia, Sunflower, French Marigold, African Marigold, Cockscomb, Cosmos

Sep. 01, 2004 36.23 23.57 29.90 13.85 9.35

Sep. 15, 2004 Oct. 01, 2004

29.74 19.10 24.42 12.72 8.32 Oct. 15, 2004 Nov. 01, 2004

26.97 10.67 18.82 11.99 7.31 Nov. 15, 2004 Dec. 01, 2004

22.48 6.77 14.63 11.75 7.13 Dec. 15, 2004 Jan. 01, 2005

18.81 4.03 11.42 12.12 7.23 Jan. 15, 2005

February 2005 18.96 6.96 12.96 12.52 7.33

Moss Rose, Pansy, Snapdragon, Petunia, Annual Verbena, Pot Marigold, Annual Phlox, Oriental Poppy, Cornflower, Flax

Mar. 01, 2005 26.19 13.29 19.74 13.30 8.43

Mar. 15, 2005 Apr. 01, 2005

32.87 15.73 24.30 14.21 9.45 Apr. 15, 2005 May 01, 2005

36.39 20.35 28.37 15.40 9.40 May 15, 2005 Jun. 01, 2005

42.27 30.70 36.48 15.76 9.99 Jun. 15, 2005 Jul. 01, 2005

36.77 25.68 31.23 15.74 9.42 Jul. 15, 2005

August 2005 37.48 30.23 33.85 14.66 9.06

September 2005 36.03 24.50 30.27 13.85 9.62

October 2005 33.16 17.13 25.15 12.72 8.75

November 2005 26.87 9.53 18.20 11.99 7.53

Table 4.1.2 Environmental detail of experiment 4.1 (2005-2006).

Growing Season Diurnal temperature (°C) Ambient

day length (h.d-1)

Daily light integral

(MJ.m-2.d-1) Maximum Minimum Average

Zinnia, Sunflower, French Marigold, African Marigold, Cockscomb, Cosmos

Sep. 01, 2005 36.03 24.47 30.25 13.85 9.62

Sep. 15, 2005 Oct. 01, 2005

33.10 17.13 25.11 12.72 8.75 Oct. 15, 2005 Nov. 01, 2005

26.87 9.53 18.20 11.99 7.53 Nov. 15, 2005 Dec. 01, 2005

22.19 2.90 12.55 11.75 7.34 Dec. 15, 2005 Jan. 01, 2006

20.03 9.29 14.66 12.12 7.13 Jan. 15, 2006

February 2006 26.64 9.00 17.82 12.52 7.03

Moss Rose, Pansy, Snapdragon, Petunia, Annual Verbena, Pot Marigold, Annual Phlox, Oriental Poppy, Cornflower, Flax

Mar. 01, 2006 26.68 12.58 19.63 13.30 8.20

Mar. 15, 2006 Apr. 01, 2006

35.23 18.40 26.82 14.21 9.67 Apr. 15, 2006 May 01, 2006

41.87 25.45 33.66 15.40 9.64 May 15, 2006 Jun. 01, 2006

41.33 25.37 33.35 15.76 9.86 Jun. 15, 2006 Jul. 01, 2006

40.65 27.39 34.02 15.74 9.23 Jul. 15, 2006

August 2006 38.29 26.74 32.52 14.66 9.31

September 2006 37.53 23.97 30.75 13.85 9.69

October 2006 33.61 20.58 27.10 12.72 8.53

November 2006 26.50 12.77 19.63 11.99 7.48

4.1.3 Results

Time taken to flowering by SDPs such as Zinnia cv. Lilliput [Fig 4.1.1(A)],

Sunflower cv. Elf [Fig 4.1.1(B)], French Marigold cv. Orange Gate [Fig 4.1.2(A)],

African Marigold cv. Crush [Fig 4.1.2(B)], Cockscomb cv. Bombay [Fig 4.1.3(A)],

Cosmos cv. Sonata Pink [Fig 4.1.3(B)] was increased significantly (P<0.05) when

seeds were sown at later dates i.e., 1st and 15th January. However, a non-significant

trend was observed from 1st September to 15th December sowing dates in almost

all cultivars of SDPs.

A 19 days difference between early sowing dates and that of 15th January was

recorded in Zinnia cv. Lilliput [Fig 4.1.1(A)]. Early planting zinnia (1st September

to 1st December) took 70-71 day to flower. There was a significant (P<0.05)

increase in time to flowering from 15th December sowing dates to 15th January.

Seeds sown on 15th December took 76 days to flower whereas 1st and 15th January

sowing dates took 81 and 89 days to flower respectively. Fig 4.1.1(B) showed 19

days difference between early sowing dates (September-December) and late

sowing date (15th January) in Sunflower cv. Elf. Sunflower grown on 1st and 15th

September took 73 and 72 days respectively whereas sunflower grown from 1st

October to 1st December flowered after 71 days and that of 15th December to 15th

January took 76 (15th December), 82 (1st January) and 90 days (15th January) to

flower.

Difference between early sowing date and late one was 11 days regarding days to

flowering of French Marigold cv. Orange Gate [Fig 4.1.2(A)]. Early sowing date,

from 1st September to 15th December took 60-62 days to flower whereas late

sowing dates such as 1st December and 15th December produced flowers after 72

and 78 days respectively, which were significantly (P<0.05) different with rest of

the sowing dates. A similar trend was observed in African Marigold cv. Crush [Fig

4.1.2(B)] and a 13 days difference in time to flower was noted between early

(September-December) and late (January) sowing dates. Plants sown between 1st

September to 15th December took 66-68 days to flower whereas time to flowering

significantly (P<0.05) increase in later sowing dates i.e., 1st January (72 days) and

15th January (79 days).

Fig 4.1.3(A) depicted a 13 days difference between 1st September to 15th December

(94-95 days) sowing date and that of 15th January one (110 days) in Cockscomb

cv. Bombay. Early planting cockscomb (1st September to 1st December) took 94-95

day to flower. After 1st December a significant (P<0.05) increase in flowering time

was observed in the following plantings on 15th December (99 days), 1st January

(104 days) and 15th January (110 days). Similarly, Fig 4.1.3(B) showed a 15 days

difference between early sowing dates (1st September to 1st December) and late

sowing date (15th January) in Cosmos cv. Sonata Pink. Cosmos grown on 1st

September to 1st December took 59-61 days to flower. Time to flowering increased

significantly (P<0.05) at later sowing dates of 15th December (65 days), 1st January

(69 days) and 15th January (74 days).

Late seed sowing indicated a statistically significant (P<0.05) difference in

flowering time in LDPs such as Moss Rose cv. Sundance [Fig 4.1.4(A)], Pansy cv.

Baby Bingo [Fig 4.1.4(B)], Snapdragon cv. Coronette [Fig 4.1.5(A)], Petunia cv.

Dreams [Fig 4.1.5(B)], Pot Marigold cv. Resina [Fig 4.1.6(A)], Annual Phlox cv.

Astoria Magenta [Fig 4.1.6(B)], Cornflower cv. Florence Blue [Fig 4.1.7(A)],

Oriental Poppy cv. Burning Heart [Fig 4.1.7(B)], Flax cv. Scarlet Flax [Fig

4.1.8(A)] and Annual Verbena cv. Obsession [Fig 4.1.8(A)]. Non-significant

difference was also observed from 1st September to 15th December sowing dates in

most cultivars of LDPs.

Plants of Moss Rose cv. Sundance flowered 10 days late when grown on 15th July

as compared to early sowing dates from March to June [Fig 4.1.4(A)]. Plants of

early sowing dates (1st and 15th March and 1st April) flowered after 59, 57 and 56

days however it took 55 days to flower (15th April to 1st June) afterward. A

significant (P<0.05) increase in flowering time was observed when plants were

grown on 1st and 15th July as they took 60 and 65 days to bloom. Similarly, Pansy

cv. Baby Bingo [Fig 4.1.4(B)] took 50 days to flower in early sowing dates as

compared to 60 days in late sowing time (10 days difference). Plants of early

sowing dates (1st and 15th March) took 52-54 days to flower however plants grown

from April to June took 50-51 days to flower. A significant (P<0.05) difference in

flowering time was observed from 1st July (55 days) to 15th July (60 days) sowing

dates.

Fourteen (14) days difference between early sowing dates and late one (15th July)

was recorded in Snapdragon cv. Coronette [Fig 4.1.5(A)]. Plants took 82 days to

flower in early sowing dates 1st and 15th March and 1st April. Flowering time was

reduced (79-80 days) in subsequent sowing dates i.e., from 15th April to 15th May.

However, it increased significantly (P<0.05) after 15th June to 15th July showing 85

days (15th June), 90 days (1st July) and 93 days (15th July). A 13 days early

flowering was recorded in Petunia cv. Dreams [Fig 4.1.5(B)] when they were sown

between 1st May and 1st June and took 55 days to flower. Plants of earlier sowing

dates (1st March to 15th April) took 56-58 days to flower. Time to flowering

significantly (P<0.05) increased from 60 to 68 days when petunia was grown at

later dates i.e. 15th June to 15th July.

A 10 days difference between early sowing time (March to June) and late sowing

time (15th July) was observed in Pot Marigold cv. Resina [Fig 4.1.6(A)]. Plants of

early sowing dates (1st March to 15th June) flowered after 70-71 days. However, a

significant (P<0.05) increase in flowering time was observed when plants were

grown on 1st and 15th July taking 75 and 80 days to flower. Similarly, Annual

Phlox cv. Astoria Magenta [Fig 4.1.6(B)] took 70-71 days to flower in early

sowing dates (1st March to 15th June) as compared to 76 and 81 days in late sowing

time of 1st to 15th July (10 days late flowering). The flowering time difference

between July and rest of the months (March-June) was statistically significant

(P<0.05).

Time to flowering was increased up to 9 days when Cornflower (cv. Florence

Blue) was planted late (15th July). Fig 4.1.7(A) showed that plants sown between

1st March to 15th June took 79-80 days to flower however on 1st July sowing date it

took 84 followed by 88 days (15th July) which was significantly (P<0.05) different

from the rest of sowing time i.e., 1st March to 15th June. On the other hand,

Oriental Poppy cv. Burning Heart took 64 days to flower in early sowing dates (1st

March to 15th June) as compared to 75 days in late sowing date (11 days

difference) [Fig 4.1.7(B)]. Plants of early sowing dates (1st March to 15th June)

took 64-65 days to flower. However, a significant (P<0.05) difference in flowering

time was observed from 1st July (70 days) to 15th July (75 days) sowing dates.

Flax cv. Scarlet Flax flowered 12 days earlier when grown between 1st March to

15th June [Fig 4.1.8(A)]. Plants of the referred sowing dates took 80-83 days to

flower, which was significantly (P<0.05) different than those grown during 1st and

15th July taking 88 and 93 days to flower respectively. On the other side, Annual

Verbena cv. Obsession showed 10 days significant difference (P<0.05) between

last sowing date (15th July) and the rest [Fig 4.1.8(B)]. There was a non-significant

difference among plants grown on earlier dates (1st March to 15th June) taking 50

days to flower. However, time to flowering was accelerated 5 to 10 days when

plants were sown at 1st and 15th July (54 and 60 days to flower, respectively).

Same experiment was repeated in 2005-2006 to confirm these results and up to 5

days difference in flowering time was recorded which showed almost the same

pattern as observed in the first year of experiment (2004-2005) i.e. a non-

significant difference between the two years data. This is because of the least

difference between the two years ambient environment i.e. temperature difference

was 0.57-1.10ºC and light integrals difference was 0.10 MJ.m-2.d-1.

4.1.4 Discussion

The findings of present research showed that very late sowing of either SDPs or

LDPs increased time to flowering which is also reported in other crops

(Trongkongsin and Humphreys 1988; McDonald et al., 1994; Hemming et al.,

2008). Different cultivars (early, medium and late) of Eustoma grandiflorum were

grown year round for consistent supply to the market (Takashi et al., 1998).

However, in present study only one cultivar of each important ornamental annual

was grown for five months, which displayed flower for a long duration. For

example, SDPs such as Zinnia, Sunflower, French Marigold, African Marigold,

Cockscomb and Cosmos flowered from end of November to April. Similarly,

LDPs such as Moss Rose, Pansy, Snapdragon, Petunia, Pot Marigold, Annual

Phlox, Cornflower, Oriental Poppy, Flax and Annual Verbena flowered from end

of May to October. This year round display of colours could be further extended by

manipulating other environmental factors such as photoperiod, temperature and

light integrals (Pearson et al., 1994; Munir, 2003).

The flowering time of cultivars depends on their inherent development rate, their

response to temperature and day length, or all three factors (Thomas and Vince-

Prue, 1997). If a crop sown late it will flower late and vice versa. In present

research, first 7-8 dates of sowing in either case (SDPs and LDPs) took almost

similar days to flower because of receiving more or less same temperature, day

length and light integrals during their growing period. However, flowering time

was enhanced when plants were sown late (last 2-3 sowing dates) owing to the

same environmental factors. For example, Zinnia and Sunflower when planted

after 15th December until 15th January increased flowering time up to 19 days. The

same results were obtained with French Marigold (11 days), African Marigold (13

days), Cockscomb (15 days) and Cosmos (16 days). This indicated that when late

sowing plants completed juvenile phase and entered in to reproductive phase

(phase change) the flower induction process was entrapped because of poor

stimulus (Battey and Tooke, 2002). In this case (SDPs) day length was increased

from 12.12 to 14.21 h.d-1 and light integrals (PAR) were increased from 7.13 to

9.45 MJ.m-2.d-1. At phase change stage plants were either expecting a continuous

flow of signals (Battey and Lyndon, 1990) from leaf to apex (O’Neil, 1992) or a

small pulse is sufficient to commit induction (Bradley et al., 1997), which in the

other way round affect apex to perceive the stimulus and hence increased time to

flowering. Similar results were obtained in LDPs. Late sowings dates, from 15th

June to 15th July affected flowering time significantly. The same justification can

be mentioned here. The day length (from 16.14 to 12.39 h.d-1) and light integrals

(from 9.42 to 7.53 MJ.m-2.d-1) decreased when LDPs entered in to phase change

stage and therefore took more time to flower (Munir, 2003).

The flowering time of a cultivar will affect decisions on time of sowing. The

present investigation that SDPs require short day length and lower PAR therefore

are suitable to grow in winter and take less time to flower but the display time

could be enhanced if sown in late winter. Similarly, LDPs require long day length

and higher PAR therefore they can be grown in summer. However, their time to

flower could be extended if grow them in late summer. Almost all ornamental

annuals showed a clear flowering schedule pattern and this plant scheduling could

be used for the steady and continuous supply of these plants in the market. As a

result they could be displayed longer in the parks and gardens.

r2 = 0.94

66

70

74

78

82

86

90

Sep

01

Sep

15

Oct

01

Oct

15

Nov

01

Nov

15

Dec

01

Dec

15

Jan0

1

Jan1

5

Dates of Sowing

Day

s to

Flo

wer

ing

SED

Zinnia cv. Lilliput

A

r2 = 0.93

66

70

74

78

82

86

90

94

Sep

01

Sep

15

Oct

01

Oct

15

Nov

01

Nov

15

Dec

01

Dec

15

Jan0

1

Jan1

5

Dates of Sowing

Day

s to

Flo

wer

ing

SED

B

Sunflower cv. Elf

Fig 4.1.1(A,B) Effect of different sowing dates (day length) on the flowering time

of (A) Zinnia cv. Lilliput and (B) Sunflower cv. Elf. Each point represents the

mean of 6 replicates. Vertical bars on data points (where larger than the points)

represent the standard error within replicates whereas vertical bar (SED) showing

standard error of difference among means.

r2 = 0.91

64

66

68

70

72

74

76

78

80

Sep

01

Sep

15

Oct

01

Oct

15

Nov

01

Nov

15

Dec

01

Dec

15

Jan0

1

Jan1

5

Dates of Sowing

Day

s to

Flo

wer

ing

SED

A

French Marigold cv. Orange Gate

r2 = 0.89

64

66

68

70

72

74

76

78

80

Sep

01

Sep

15

Oct

01

Oct

15

Nov

01

Nov

15

Dec

01

Dec

15

Jan0

1

Jan1

5

Dates of Sowing

Day

s to

Flo

wer

ing

SED

B

African Marigold cv. Crush

Fig 4.1.2(A,B) Effect of different sowing dates (day length) on

the flowering time of (A) French Marigold cv. Orange Gate and

(B) African Marigold cv. Crush. Each point represents the mean of

6 replicates. Vertical bars on data points (where larger than the

points) represent the standard error within replicates whereas

vertical bar (SED) showing standard error of difference among

means.

r2 = 0.96

92

94

9698

100

102

104

106108

110

112S

ep01

Sep

15

Oct

01

Oct

15

Nov

01

Nov

15

Dec

01

Dec

15

Jan0

1

Jan1

5

Dates of Sowing

Day

s to

Flo

wer

ing

SED

A

Cockscomb cv. Bombay

r2 = 0.93

58

60

62

64

66

68

70

72

74

76

Sep

01

Sep

15

Oct

01

Oct

15

Nov

01

Nov

15

Dec

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Dec

15

Jan0

1

Jan1

5

Dates of Sowing

Day

s to

Flo

wer

ing

SED

B

Cosmos cv. Sonata Pink


of (A) Cockscomb cv. Bombay and (B) Cosmos cv. Sonata Pink. Each point

represents the mean of 6 replicates. Vertical bars on data points (where larger than

the points) represent the standard error within replicates whereas vertical bar

(SED) showing standard error of difference among means.

r2 = 0.92

52

54

56

58

60

62

64

66

Mar

01

Mar

15

Apr

01

Apr

15

May

01

May

15

Jun0

1

Jun1

5

Jul0

1

Jul1

5

Dates of Sowing

Day

s to

Flo

wer

ing

SED

Moss Rose cv. Sundance

A

r2 = 0.94

48

50

52

54

56

58

60

62

Mar

01

Mar

15

Apr

01

Apr

15

May

01

May

15

Jun0

1

Jun1

5

Jul0

1

Jul1

5

Dates of Sowing

Day

s to

Flo

wer

ing

SED

Pansy cv. Baby Bingo

B


of (A) Moss Rose cv. Sundance and (B) Pansy cv. Baby Bingo. Each point




r2 = 0.96

78

80

82

84

86

88

90

92

94

96

Mar

01

Mar

15

Apr

01

Apr

15

May

01

May

15

Jun0

1

Jun1

5

Jul0

1

Jul1

5

Dates of Sowing

Day

s to

Flo

wer

ing

SED

Snapdragon cv. Coronette

A

r2 = 0.93

52

54

56

58

60

62

64

66

68

70

Mar

01

Mar

15

Apr

01

Apr

15

May

01

May

15

Jun0

1

Jun1

5

Jul0

1

Jul1

5

Dates of Sowing

Day

s to

Flo

wer

ing

SED

Petunia cv. Dreams

B

Fig 4.1.5(A,B) Effect of different sowing dates (day length) on the

flowering time of (A) Snapdragon cv. Coronette and (B) Petunia

cv. Dreams. Each point represents the mean of 6 replicates.

Vertical bars on data points (where larger than the points)

represent the standard error within replicates whereas vertical bar


r2 = 0.90

68

70

72

74

76

78

80

Mar

01

Mar

15

Apr

01

Apr

15

May

01

May

15

Jun0

1

Jun1

5

Jul0

1

Jul1

5

Dates of Sowing

Day

s to

Flo

wer

ing

SED

A

Pot Marigol cv. Resina

r2 = 0.89

68

70

72

74

76

78

80

82

Mar

01

Mar

15

Apr

01

Apr

15

May

01

May

15

Jun0

1

Jun1

5

Jul0

1

Jul1

5

Dates of Sowing

Day

s to

Flo

wer

ing

SED

B

Annual Phlox cv. Astoria Magenta

Fig 4.1.6(A,B) Effect of different sowing dates (day length) on the

flowering time of (A) Pot Marigold cv. Resina and (B) Annual

Phlox cv. Astoria Magenta. Each point represents the mean of 6

replicates. Vertical bars on data points (where larger than the



means.

r2 = 0.94

76

78

80

82

84

86

88

90

Mar

01

Mar

15

Apr

01

Apr

15

May

01

May

15

Jun0

1

Jun1

5

Jul0

1

Jul1

5

Dates of Sowing

Day

s to

Flo

wer

ing

SED

A

Cornflower cv. Florence Blue

r2 = 0.85

62

64

66

68

70

72

74

76

Mar

01

Mar

15

Apr

01

Apr

15

May

01

May

15

Jun0

1

Jun1

5

Jul0

1

Jul1

5

Dates of Sowing

Day

s to

Flo

wer

ing

SED

B

Oriental Poppy cv. Burning Heart


of (A) Cornflower cv. Florence Blue and (B) Oriental Poppy cv. Burning Heart.

Each point represents the mean of 6 replicates. Vertical bars on data points (where

larger than the points) represent the standard error within replicates whereas

vertical bar (SED) showing standard error of difference among means.

r2 = 0.91

78

80

82

84

86

88

90

92

94M

ar01

Mar

15

Apr

01

Apr

15

May

01

May

15

Jun0

1

Jun1

5

Jul0

1

Jul1

5

Dates of Sowing

Day

s to

Flo

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ing

SED

A

Flax cv. Scarlet Flax

r2 = 0.83

46

48

50

52

54

56

58

60

62

Mar

01

Mar

15

Apr

01

Apr

15

May

01

May

15

Jun0

1

Jun1

5

Jul0

1

Jul1

5

Dates of Sowing

Day

s to

Flo

wer

ing

SED

Annual Verbena cv. Obsession

B

Fig 4.1.8(A,B) Effect of different sowing dates (daylength) on the flowering time

of (A) Flax cv. Scarlet Flax and (B) Nemesia cv. Safari. Each point represents the




4.2 Effects of different photoperiods on time to flowering of important ornamental annuals

4.2.1 Introduction

Flowering is the end result of physiological processes, biochemical sequences, and

gene action, with the whole system responding to the influence of environmental

stimuli (photoperiod, temperature) and the passage of time (Zheng et al., 2006).

Generally, after attaining a certain size (completing the ‘juvenile’ phase) plants

enter into the ‘reproductive’ phase (initiation and development of flowering).

Evans (1969) referred to flowering as the inductive processes occurring in the leaf,

mediated by the photoreceptor, phytochrome that leads to the initiation of

flowering at the meristem (evocation). Inductive processes occur in the leaf

(O’Neil, 1992) and result in floral initiation in which the apical meristem changes

towards floral development (McDaniel et al., 1992). It is believed that flowering is

induced by a stimulus (florigen), which is produced within the leaf (Chailakhyan,

1936) but this hormone has not yet been identified. When the apical meristem of

the plant is committed to flowering, its fate becomes irreversible (Bernier, 1988),

although flower or inflorescence reversion to vegetative growth can also occur

spontaneously in some species. This condition can be caused if plants are

transferred to certain specific photoperiod or temperature regimes, which favour

vegetative development (Battey and Lyndon, 1990).

Many flowering plants use a photoreceptor protein, such as phytochrome or

cryptochrome, to sense seasonal changes in day length (photoperiod), which they

take as signals to flower (Weller and Kendrick, 2008). The photoperiodic response

of flowering is generally categorised into three main groups: short-day plants

(SDPs) in which flowering is hastened by longer nights; long-day plants (LDPs)

where shorter nights promote flowering; and day-neutral plants (DNPs) which

flower irrespective to day length. SDPs and LDPs can be further classified as

obligate (species that require a specific minimum or maximum photoperiod for

flowering) and facultative (flowering process is hastened by a specific minimum or

maximum photoperiod).

It is actually the night length rather than day length that controls flowering, so

flowering in a long day plant is triggered by a short night (which, of course, also

means a long day). Conversely, short day plants flower when nights get longer than

a critical length. This can be observed by using night breaks. For example, a short

day plant (long night) will not flower if a pulse (5 minutes) of artificial light is

shone on the plant during the middle of the night. This generally does not occur

from natural light such as moonlight, lightning, fire flies, etc, since the light from

these sources is not sufficiently strong to trigger the response (Thomas and Vince-

Prue, 1997).

Day neutral plants do not initiate flowering based on photoperiodism i.e. they can

flower regardless of the night length; some may use temperature (vernalization)

instead. Facultative long day or short day plants will have their flowering advanced

or retarded by short or long days, but will eventually flower in sub-optimal day

lengths. Again, temperature is likely to also influence flowering time in these

plants. Modern biologists believe that it is the coincidence of the active forms of

phytochrome or cryptochrome, created by light during the daytime, with the

rhythms of the circadian clock that allows plants to measure the length of the night

(Thomas and Vince-Prue, 1997). The results of previous experiment (4.1) revealed

that flowering response of annual ornamentals altered by changing the natural day

length. Therefore, an experiment was designed to observe flowering response of

various annual ornamentals under four controlled photoperiod chambers.


The experiment was conducted in Agricultural Research Institute, Dera Ismail

Khan, Pakistan, during the year 2005 and 2006. Seeds of facultative LDPs such as

Moss Rose cv. Sundance, Pansy cv. Baby Bingo, Snapdragon cv. Coronette,

Petunia cv. Dreams, Annual Verbena cv. Obsession, obligate LDPs such as Pot

Marigold cv. Resina, Annual Phlox cv. Astoria Magenta, Cornflower cv. Florence

Blue, Oriental Poppy cv. Burning Heart and Flax cv. Scarlet Flax and facultative

SDPs such as Zinnia cv. Lilliput, Sunflower cv. Elf, French Marigold cv. Orange

Gate, African Marigold cv. Crush, Cockscomb cv. Bombay, Cosmos cv. Sonata

Pink were sown on 1st of March 2005 and 2006 into module trays containing

locally prepared leaf mould compost.

Seed trays were kept at room temperature at night and were moved out during the

day (08:00–16:00 h) under partially shaded area. After 70% seed germination, six

replicates of each cultivar were shifted to the respective photoperiod chamber.

Plants remained for 8h (from 08:00 to 16:00h) in the field (outside the photoperiod

chambers) where they were exposed to natural daylight and temperature (Table

4.2.1 and 4.2.2). At 16:00h each day, all plants were moved into the photoperiod

chambers where they remained until 08:00h the following morning. Photoperiod

within each chambers was extended by two 60Watt tungsten light bulbs and one

18Watt warm white florescent long-life bulb (Philips, Holland) fixed above 1 m

high from the trolleys providing a light intensity (PPFD) of 7mol m-2 s-1. In all

photoperiod chambers, the lamps were switched on automatically at 16:00 h for a

duration dependents on the day length required (for facultative LDPs and SDPs: 8,

11, 14, 17 h.d-1; for obligate LDPs 11, 13, 15, 17 h.d-1). These chambers were

continuously ventilated with the help of micro exhaust fan (Fan-0051,

SUPERMICRO USA) with an average air speed of 0.2 m.s-1 over the plants when

inside the chambers, to minimize any temperature increase due to heat from the

lamps. Temperature and solar radiation were measured in the weather station

situated one kilometer away from the research venue. Temperature was recorded

with the help of Hygrothermograph (NovaLynx Corporation, USA) while solar

radiation was estimated using solarimeters (Casella Measurement, UK).

Plants were potted into 9cm pots containing leaf mould compost and river sand

(3:1 v/v) after 6 leaves emerged. Water was applied by hand and a nutrient solution

[(Premium Liquid Plant Food and Fertilizer (NPK: 8-8-8); Nelson Products Inc.

USA)] was applied twice a week. Plants in each treatment were observed daily

until flower opening (corolla fully opened). Numbers of days to flowering from

emergence were recorded at harvest and the data were analysed using GenStat-8

(Lawes Agricultural Trust, Rothamsted Experimental Station, U.K. and VSN

International Ltd. U.K.).

Table 4.2.1 Environmental detail of experiment 4.2 (March 1,

2005).

Growing Season Diurnal temperature (C) Daily light integral

08:00-16:00 Maximum Minimum Average March 2005 26.19 13.29 19.74 8.43 MJ.m-2.d-1 April 2005 32.87 15.73 24.30 9.45 MJ.m-2.d-1 May 2005 36.39 20.35 28.37 9.40 MJ.m-2.d-1 June 2005 42.27 30.70 36.48 9.99 MJ.m-2.d-1 July 2005 42.27 30.70 36.48 9.42 MJ.m-2.d-1

Table 4.2.2 Environmental detail of experiment 4.2 (March 1,

2006).

Growing Season Diurnal temperature (C) Daily light integral 08:00-16:00 Maximum Minimum Average

March 2006 26.68 12.58 19.63 8.20 MJ.m-2.d-1 April 2006 35.23 18.40 26.82 9.67 MJ.m-2.d-1 May 2006 41.87 25.45 33.66 9.64 MJ.m-2.d-1 June 2006 41.33 25.37 33.35 9.86 MJ.m-2.d-1 July 2006 40.65 27.74 34.19 9.23 MJ.m-2.d-1

4.2.3 Results

4.2.3.1 Facultative long day plants

Findings of this experiment illustrated a statistically significant (P<0.05) difference

among four photoperiods regarding flowering time in facultative LDPs such as

Moss Rose cv. Sundance [Fig 4.2.1(A)], Pansy cv. Baby Bingo [Fig 4.2.1(B)],

Snapdragon cv. Coronette [Fig 4.2.2(A)], Petunia cv. Dreams [Fig 4.2.2(B)],

Annual Verbena cv. Obsession [Fig 4.2.3(A)]. Flowering time was enhanced when

these LDPs were grown under short day environment (8 h.d-1) whereas it was

decreased significantly under long day environment (17 h.d-1).

Moss Rose cv. Sundance [Fig 4.2.1(A)] grown under 8 h.d-1 photoperiod flowered

after 74 days as compared to 17 h.d-1 photoperiod plants (61 days). Similarly,

plants grown under 14 and 11 h.d-1 photoperiod flowered after 63 and 67 days from

emergence respectively. Pansy cv. Baby Bingo [Fig 4.2.1(B)] flowered after 55

days when grown in 17 h.d-1 photoperiod than those plants which were raised in

SD i.e. 8 h.d-1 photoperiod (70 days). Same plants when grown in 14 and 11 h.d-1

photoperiod took 58 and 64 days to flower respectively. Plants took 91 days to

flower when Snapdragon cv. Coronette [Fig 4.2.2(A)] were grown under LD i.e. 17

h.d-1 photoperiod as compared to 8 h.d-1 photoperiod (120 days). Plants of the same

cultivar took 95 and 110 days to flower when grown under 14 and 11 h.d-1

photoperiod respectively. Petunia cv. Dreams [Fig 4.2.2(B)] when grown under 8

h.d-1 photoperiod flowered after 76 days from emergence whereas plants received

17 h.d-1 photoperiod flowered after 60 days. However, plants grown under 14 and

11 h.d-1 photoperiod took 63 and 70 days to flower respectively. Fig 4.2.3(A)

depicted that Annual Verbena cv. Obsession flowered after 66 days under SD i.e. 8

h.d-1 photoperiod as compared to 17 h.d-1 photoperiod (50 days). Similarly, plants

received 14 and 11 h.d-1 photoperiod flowered after 53 and 58 days respectively.

Data of facultative LDPs were analysed using the following model:

1/f = a + bP

The best fitted model describing the effects of mean photoperiod (P) on the rate of

progress to flowering (1/f) can be written as:

Moss Rose cv. Sundance [Fig 4.2.9(A) and Fig 4.2.17(A)]:

1/f = 105.47 (±1.97) + [- 1.48 (±0.15)] P (r2 = 0.99, d.f. 23) 4.2.1

Pansy cv. Baby Bingo [Fig 4.2.9(B) and Fig 4.2.17(B)]:

1/f = 104.14 (±1.94) + [- 1.71 (±0.15)] P (r2 = 0.99, d.f. 23) 4.2.2

Snapdragon cv. Coronette [Fig 4.2.10(A) and Fig 4.2.18(A)]:

1/f = 146.50 (±2.63) + [- 3.42 (±0.20)] P (r2 = 0.99, d.f. 23) 4.2.3

Petunia cv. Dreams [Fig 4.2.10(B) and Fig 4.2.18(B)]:

1/f = 111.64 (±2.38) + [- 1.86 (±0.18)] P (r2 = 0.99, d.f. 23) 4.2.4

Annual Verbena cv. Obsession [Fig 4.2.11(A) and Fig 4.2.19(A)]:

1/f = 78.94 (±2.00) + [- 1.76 (±0.16)] P (r2 = 0.99, d.f. 23) 4.2.5

Above equations 4.2.1-4.2.5 are based on individual arithmetic means of respective

factors, although all data were originally tested. The values in parenthesis show the

standard errors of the regression coefficients. The outcome of this model indicated

that photoperiod had significant effects on the rate of progress to flowering in all

facultative LDPs studied. For validation of the model actual data of rate of

progress to flowering were plotted against the predicted ones to develop a fitted

relationship and almost all values were successfully plotted near the line of identity

which also showed that the photoperiod had a significant effect on the rate of

progress to flowering.

4.2.3.2 Obligate long day plants

Results of present work indicated that there was a statistically significant (P<0.05)

difference among four photoperiods regarding flowering time in obligate LDPs

such as Pot Marigold cv. Resina [Fig 4.2.3(B)], Annual Phlox cv. Astoria Magenta

[Fig 4.2.4(A)], Cornflower cv. Florence Blue [Fig 4.2.4(B)], Oriental Poppy cv.

Burning Heart [Fig 4.2.5(A)] and Flax cv. Scarlet Flax [Fig 4.2.5(B)]. Time to

flowering was increased significantly when these LDPs were grown under SD

environment (11 h.d-1), however it was gradually decreased when they were grown

in 13, 15 and 17 h.d-1 photoperiod chambers.

Flowering time was increased up to 100 days when Pot Marigold cv. Resina [Fig

4.2.3(B)] was grown under 11 h.d-1 photoperiod and 75 days in 17 h.d-1

photoperiod. Similarly, plants received 13 and 15 h.d-1 photoperiod flowered after

88 and 77 days respectively. Long days, 17 h.d-1 photoperiod hastened flowering

time (75 days) in Annual Phlox cv. Astoria Magenta [Fig 4.2.4(A)] as compared to

11 h.d-1 photoperiod (99 days). Plants grown in 13 and 15 h.d-1 photoperiod

flowered in 87 and 75 days respectively. Similarly, time to flowering was

increased (108 days) when plants of Cornflower cv. Florence Blue [Fig 4.2.4(B)]

were grown under 11 h.d-1 photoperiod as compared to 17 h.d-1 photoperiod (86

days). Plants grown in 13 and 15 h.d-1 photoperiod took 96 and 88 days to flower

respectively. Oriental Poppy cv. Burning Heart [Fig 4.2.5(A)] flowered after 72

days in 17 h.d-1 photoperiod followed by 73 days in 15 h.d-1 photoperiod.

However, in 11 h.d-1 photoperiod plants bloomed after 96 days from emergence

followed by 84 days in 13 h.d-1 photoperiod. Similarly, 11 h.d-1 photoperiod (110

days) delayed flowering time in Flax cv. Scarlet Flax [Fig 4.2.5(B)] as compared to

17 h.d-1 photoperiod (86 days) whereas plants grown in 13 and 15 h.d-1

photoperiod took 98 and 88 days to flower respectively.

Data from obligate LDPs were analysed using the following model:

1/f = a + bP



Pot Marigold cv. Resina [Fig 4.2.11(B) and Fig 4.2.19(B)]:

1/f = 120.86 (±2.87) + [- 2.87 (±0.22)] P (r2 = 0.97, d.f. 23) 4.2.6

Annual Phlox cv. Astoria Magenta [Fig 4.2.12(A) and Fig 4.2.20(A)]:

1/f = 118.72 (±3.18) + [- 2.79 (±0.25)] P (r2 = 0.98, d.f. 23) 4.2.7

Cornflower cv. Florence Blue [Fig 4.2.12(B) and Fig 4.2.20(B)]:

1/f = 124.72 (±2.93) + [- 2.43 (±0.23)] P (r2 = 0.99, d.f. 23) 4.2.8

Oriental Poppy cv. Burning Heart [Fig 4.2.13(A) and Fig 4.2.21(A)]:

1/f = 116.36 (±3.03) + [- 2.82 (±0.24)] P (r2 = 0.98, d.f. 23) 4.2.9

Flax cv. Scarlet Flax [Fig 4.2.13(B) and Fig 4.2.21(B)]:

1/f = 129.94 (±2.55) + [- 2.76 (±0.20)] P (r2 = 0.99, d.f. 23) 4.2.10

Above equations 4.2.6-4.2.10 are based on individual arithmetic means of

respective factors, although all data were originally tested. The values in

parenthesis show the standard errors of the regression coefficients. The outcome of

this model indicated that photoperiod had significant effects on the rate of progress

to flowering in all obligate LDPs studied. For validation of the model actual data of

rate of progress to flowering were plotted against the predicted ones to develop a

fitted relationship and almost all values were successfully plotted near the line of

identity which also showed that the photoperiod had a significant effect on the rate

of progress to flowering.

4.2.3.3 Facultative short day plants

Time to flowering in SDPs such as Zinnia cv. Lilliput [Fig 4.2.6(A)], Sunflower

cv. Elf [Fig 4.2.6(B)], French Marigold cv. Orange Gate [Fig 4.2.7(A)], African

Marigold cv. Crush [Fig 4.2.7(B)], Cockscomb cv. Bombay [Fig 4.2.8(A)] and

Cosmos cv. Sonata Pink [Fig 4.2.8(B)] was increased significantly (P<0.05) with

increase in photoperiod. Plants received maximum duration of light took highest

time to flower whereas it decreased significantly under minimum photoperiod.

It was observed that Zinnia cv. Lilliput [Fig 4.2.6(A)] flowered after 64 days under

SD i.e. 8 h.d-1 photoperiod as compared to LD i.e. 17 h.d-1 photoperiod (80 days)

followed by 14 h.d-1 photoperiod (78 days) and 11 h.d-1 photoperiod (70 days).

Similarly, Fig 4.2.6(B) showed that Sunflower cv. Elf took 64 days to flower under

8 h.d-1 photoperiod however plant under 17 h.d-1 photoperiod flowered after 79

days. Plants grown in 14 and 11 h.d-1 photoperiod flowered after 69 and 75 days

respectively. French Marigold cv. Orange Gate [Fig 4.2.7(A)] flowered after 59

days under 8 h.d-1 photoperiod as compared to 17 h.d-1 photoperiod (69 days)

followed by 14 and 11 h.d-1 photoperiod i.e. 64 and 62 days respectively.

Similarly, African Marigold cv. Crush [Fig 4.2.7(B)] grown under 8 h.d-1

photoperiod took 60 days to flower than 17 h.d-1 photoperiod (71 days). Plants of

same cultivar took 70 and 63 days to flower when grown under 14 and 11 h.d-1

photoperiod. Flowering time under 8 h.d-1 photoperiod was recorded as 87 days in

Cockscomb cv. Bombay [Fig 4.2.8(A)] as compared to 101 days in 17 h.d-1

photoperiod followed by 95 days in 14 h.d-1 photoperiod and 92 days in 11 h.d-1

photoperiod. Similarly, Cosmos cv. Sonata Pink [Fig 4.2.8(B)] when grown under

8 h.d-1 photoperiod flowered after 55 days as compared to 17 h.d-1 photoperiod (83

days) whereas plants grown under 14 and 11 h.d-1 photoperiod bloomed after 73

and 63 days from emergence respectively.

Data from facultative SDPs were analysed using the following model:

1/f = a + bP



Zinnia cv. Lilliput [Fig 4.2.14(A) and Fig 4.2.22(A)]:

1/f = 70.67 (±1.92) + 1.88 (±0.15)] P (r2 = 0.97, d.f. 23) 4.2.11

Sunflower cv. Elf [Fig 4.2.14(B) and Fig 4.2.22(B)]:

1/f = 71.92 (±1.77) + 1.65 (±0.14)] P (r2 = 0.99, d.f. 23) 4.2.12

French Marigold cv. Orange Gate [Fig 4.2.15(A) and Fig 4.2.23(A)]:

1/f = 50.00 (±1.84) + 1.07 (±0.14)] P (r2 = 0.99, d.f. 23) 4.2.13

African Marigold cv. Crush [Fig 4.2.15(B) and Fig 4.2.23(B)]:

1/f = 70.31 (±2.35) + 1.32 (±0.18)] P (r2 = 0.95, d.f. 23) 4.2.14

Cockscomb cv. Bombay [Fig 4.2.16(A) and Fig 4.2.24(A)]:

1/f = 96.17 (±1.98) + 1.47 (±0.15)] P (r2 = 0.98, d.f. 23) 4.2.15

Cosmos cv. Sonata Pink [Fig 4.2.16(B) and Fig 4.2.24(B)]:

1/f = 28.83 (±2.39) + 3.17 (±0.19)] P (r2 = 0.99, d.f. 23) 4.2.16

Above equations 4.2.11-4.2.16 are based on individual arithmetic means of

respective factors, although all data were originally tested. The values in

parenthesis show the standard errors of the regression coefficients. The outcome of

this model indicated that photoperiod had significant effects on the rate of progress

to flowering in all facultative SDPs studied. For validation of the model actual data

of rate of progress to flowering were plotted against the predicted ones to develop

a fitted relationship and almost all values were successfully plotted near the line of

identity which also showed that the photoperiod had a significant effect on the rate

of progress to flowering.

Same experiment was repeated in March 2006 to confirm these results and up to 3


pattern as observed in the first year of experiment (March 2005). Therefore, the

difference between two years data was non-significant statistically. This is because

of the least difference between the two years ambient environment i.e. temperature

difference was 0.46ºC and light integrals difference was 0.02 MJ.m-2.d-1.

4.2.4 Discussion

Flower development at the shoot apex is initiated in response to environmental

cues. Photoperiod (day length) is one of the most important of these and is

perceived in the leaves (O’Neil, 1992). A systemic signal, called the floral

stimulus, is then transmitted from the leaves through the phloem and induces floral

development at the shoot apex (An et al., 2004). Cultivars of Moss Rose, Pansy,

Snapdragon, Petunia and Annual Verbena showed a facultative long day response

i.e. long days enhanced flowering process whereas cultivars of Pot Marigold,

Annual Phlox, Cornflower, Oriental Poppy and Flax appeared as an obligate long

plants i.e. long days indispensable for flowering. Similarly, cultivars of Zinnia,

Sunflower, French and African Marigolds, Cockscomb and Cosmos displayed a

facultative short day response i.e. short days enhanced flowering process. These

results are in line with the findings of Erwin and Warner (2002). Facultative LDPs

flowered 13 (Moss Rose), 15 (Pansy), 29 (Snapdragon) and 16 days (Petunia and

Annual Verbena) earlier in LD environment (17 h.d-1), similarly obligate LDPs

flowered 25 (Pot Marigold and Oriental Poppy), 24 (Annual Phlox and Flax) and

22 days (Cornflower) earlier in the same LD environment. However, facultative

SDPs flowered 16 (Zinnia), 15 (Sunflower), 10 (French Marigold), 11 (African

Marigold), 14 (Cockscomb) and 29 days (Cosmos) earlier when grown in SD

environment (8 h.d-1).

The response of LDPs observed in present study supporting the fact that these

plants are from Mediterranean or temperate origin where the day

length/photoperiod is much longer than in the tropics and plants originating from

this region prefer an open environment with ample sunshine. Similarly, current

knowledge suggested that most SDPs are of tropical or sub-tropical origin

(Summerfield et al., 1997). Studies have been carried out previously to support this

evidence in Pansy (Adams et al., 1997), Snapdragon (Cremer et al., 1998; Munir,

2003), Petunia (Adams et al., 1997b; Shimai, 2001; Donnelly and Fisher, 2002),

Annual Verbena (Donnelly and Fisher, 2002), Annual Phlox (Runkle et al., 1998),

Oriental Poppy (Gentner et al., 1975; Acock et al., 1996; Wang et al., 1998, 1999),

Flax (Kurt and Bozkurt, 2006), Zinnia (Young et al., 2003), Sunflower (Young et

al., 2003; Yañez et al., 2004), French and African Marigold (Tsukamoto et al.,

1968, 1971), Cockscomb (Kanellos and Pearson, 2000; Young et al., 2003; Goto

and Muraoka, 2008) and Cosmos (Warner, 2006).

LDPs grown under inductive environment (17 h.d-1 photoperiod) induced

flowering earlier than those grown below this. Similarly, inductive environment (8

h.d-1 photoperiod) significantly enhanced flowering process in SDPs. The reason of

early flowering under inductive environment is due to the stimulation of floral

genes which are implicated in the transition of flowering (phase change) are those

that encode photoreceptors. These photoreceptors are the phytochrome, which

perceive red (660nm) and far-red (730nm) light, and the cryptochromes, which

perceive UV-A and blue light. It is reported in Arabidopsis that the phytochromes

A and B along with the cryptochromes 1 and 2 are involved in the photoperiodic

response (Mouradov et al., 2002). Therefore, any descending (in LDPs) or

ascending (SDPs) alteration in photoperiod from the optimum one affect plant’s

perception of light and can delay phase change from juvenile to flowering. In

general, far-red and blue light promote flowering in Arabidopsis whereas red light

inhibits flowering (Lin, 2000). An et al. (2004) identified a pathway of genes

required for the initiation of flowering in response to photoperiod in Arabidopsis.

The nuclear zinc-finger protein CONSTANS (CO) plays a central role in this

pathway and in response to long days activates the transcription of FT

(FLOWERING LOCUS T) gene, which encodes a RAF-kinase-inhibitor-like

protein. After the activation of FT, CO regulates the synthesis or transport of a

systemic flowering signal, thereby positioning this signal within the established

hierarchy of regulatory proteins that controls flowering.

The transduction of the light signals involves a complex web of interactions

between photoreceptors and their corresponding interacting proteins. In term of

floral induction, perception of photoperiod appears to be one of the most important

transducers of the plant’s environment. An important mechanism used by the

plants phytochromes and cryptochromes to communicate photoperiod activity

involves the entrainment of the circadian rhythms, a self-reinforcing endogenous

clock that allows light/dark coordinated gene expression. Mizoguchi et al. (2005)

reported that GIGANTEA (GI) gene regulates circadian rhythms and acts earlier in

the hierarchy than CO and FT and suggested that GI acts between the circadian

oscillator and CO to promote flowering by increasing CO and FT mRNA

abundance.

These studies established an understanding that different genes control flowering

process and these genes are evoked when a leaf is fated to respond to the inductive

photoperiod, the leaf exports floral stimulus towards apex. In most cases, when the

photoperiod becomes non-inductive, the leaf stops exporting signal. The important

developmental event in leaf formation, as far as photoperiodic induction is

concerned, appears to be the commitment of a leaf to develop the capacity to

respond to the inductive photoperiod (McDaniel, 1996). In present study, it is

revealed that after completing the juvenile phase (attaining a specific leaf numbers)

the competent leaf (newly developed one) respond to the inductive photoperiod

(day length) and induced floral signal toward apex to produce flower that is why an

early flowering response was observed under inductive photoperiod environment

in both LDPs and SDPs.

r2 = 0.99

58

60

62

64

66

68

70

72

74

76

8 11 14 17

Photoperiods (h.d-1)

Day

s to

flo

wer

ing

SED


A

r2 = 0.99

54

56

58

60

62

64

66

68

70

72

8 11 14 17


Day

s to

flo

wer

ing

SED


B

Fig 4.2.1(A,B) Effect of different photoperiods on the flowering time of (A) Moss

Rose cv. Sundance and (B) Pansy cv. Baby Bingo. Each point represents the mean

of 6 replicates. Vertical bars on data points (where larger than the points) represent

the standard error within replicates whereas vertical bar (SED) showing standard

error of difference among means.

r2 = 0.97

88

92

96

100

104

108

112

116

120

124

8 11 14 17


Day

s to

flo

wer

ing

SED


A

r2 = 0.99

58

60

62

64

66

68

70

72

74

76

78

8 11 14 17


Day

s to

flo

wer

ing

SED

Petunia cv. Dreams

B

Fig 4.2.2(A,B) Effect of different photoperiods on the






r2 = 0.99

48

50

52

54

56

58

60

62

64

66

68

8 11 14 17


Day

s to

flo

wer

ing

SED


A

r2 = 0.97

72

76

80

84

88

92

96

100

104

11 13 15 17


Day

s to

flo

wer

ing

SED


B


flowering time of (A) Annual Verbena cv. Obsession and (B) Pot

Marigold cv. Resina. Each point represents the mean of 6




means.

r2 = 0.98

72

76

80

84

88

92

96

100

11 13 15 17


Day

s to

flo

wer

ing

SED


A

r2 = 0.99

84

88

92

96

100

104

108

112

11 13 15 17


Day

s to

flo

wer

ing

SED

B


Fig 4.2.4(A,B) Effect of different photoperiods on the flowering time of (A)

Annual Phlox cv. Astoria Magenta and (B) Cornflower cv. Florence Blue. Each

point represents the mean of 6 replicates. Vertical bars on data points (where larger

than the points) represent the standard error within replicates whereas vertical bar


r2 = 0.98

70

74

78

82

86

90

94

98

11 13 15 17


Day

s to

flo

wer

ing

SED


A

r2 = 0.99

84

88

92

96

100

104

108

112

11 13 15 17


Day

s to

flo

wer

ing

SED


B


Oriental Poppy cv. Burning Heart and (B) Flax cv. Scarlet Flax. Each point




r2 = 0.97

62

64

66

68

70

72

74

76

78

80

82

8 11 14 17


Day

s to

flo

wer

ing

SED

Zinnia cv. Lilliput

A

r2 = 0.99

62

64

66

68

70

72

74

76

78

80

8 11 14 17


Day

s to

flo

wer

ing

SED

Sunflower cv. Elf

B


Zinnia cv. Lilliput and (B) Sunflower cv. Elf. Each point represents the mean of 6

replicates. Vertical bars on data points (where larger than the points) represent the

standard error within replicates whereas vertical bar (SED) showing standard error

of difference among means.

r2 = 0.99

56

58

60

62

64

66

68

70

8 11 14 17


Day

s to

flo

wer

ing

SED


A

r2 = 0.95

58

60

62

64

66

68

70

72

8 11 14 17


Day

s to

flo

wer

ing

SED


B


flowering time of (A) French Marigold cv. Orange Gate and (B)

African Marigold cv. Crush. Each point represents the mean of 6




means.

r2 = 0.98

84

86

88

90

92

94

96

98

100

102

8 11 14 17


Day

s to

flo

wer

ing

SED


A

r2 = 0.99

52

56

60

64

68

72

76

80

84

8 11 14 17


Day

s to

flo

wer

ing

SED


B


Cockscomb cv. Bombay and (B) Cosmos cv. Sonata Pink. Each point represents

the mean of 6 replicates. Vertical bars on data points (where larger than the points)



r2 = 0.99

0.013

0.014

0.015

0.016

0.017

8 11 14 17


Rat

e of

pro

gres

s to

flo

wer

ing

(1/f

) Moss Rose cv. Sundance

A

r2 = 0.99

0.013

0.014

0.015

0.016

0.017

0.018

0.019

8 11 14 17


Rat

e of

pro

gres

s to

flo

wer

ing

(1/f)


B

Fig 4.2.9(A,B) Effect of different photoperiods on the rate of progress to

flowering (1/f) of (A) Moss Rose cv. Sundance and (B) Pansy cv. Baby Bingo.


larger than the points) represent the standard error within replicates.

r2 = 0.97

0.0080

0.0085

0.0090

0.0095

0.0100

0.0105

0.0110

0.0115

8 11 14 17


Rat

e of

pro

gres

s to

flo

wer

ing

( 1/f

) Snapdragon cv. Coronette

A

r2 = 0.99

0.0125

0.0130

0.0135

0.0140

0.0145

0.0150

0.0155

0.0160

0.0165

0.0170

8 11 14 17


Rat

e of

pro

gres

s to

flo

wer

ing

(1/f)

Petunia cv. Dreams

B

Fig 4.2.10(A,B) Effect of different photoperiods on the rate of

progress to flowering (1/f) of (A) Snapdragon cv. Coronette and

(B) Petunia cv. Dreams. Each point represents the mean of 6


points) represent the standard error within replicates.

r2 = 0.99

0.0140

0.0150

0.0160

0.0170

0.0180

0.0190

0.0200

0.0210

8 11 14 17


Rat

e of

pro

gres

s to

flo

wer

ing

(1/f)


A

r2 = 0.97

0.00960.01000.01040.01080.01120.01160.01200.01240.01280.01320.01360.0140

11 13 15 17


Rat

e of

pro

gres

s to

flo

wer

ing

(1/f)


B


progress to flowering (1/f) of (A) Annual Verbena cv. Obsession

and (B) Pot Marigold cv. Resina. Each point represents the mean

of 6 replicates. Vertical bars on data points (where larger than the

points) represent the standard error within replicates.

r2 = 0.97

0.0090

0.0096

0.0102

0.0108

0.0114

0.0120

0.0126

0.0132

0.0138

11 13 15 17


Rat

e of

pro

gres

s to

flo

wer

ing

(1/f)


A

r2 = 0.99

0.0090

0.0094

0.0098

0.0102

0.0106

0.0110

0.0114

0.0118

11 13 15 17


Rat

e of

pro

gres

s to

flo

wer

ing

(1/f)


B


flowering (1/f) of (A) Annual Phlox cv. Astoria Magenta and (B) Cornflower cv.

Florence Blue. Each point represents the mean of 6 replicates. Vertical bars on data

points (where larger than the points) represent the standard error within replicates.

r2 = 0.99

0.0090

0.0095

0.0100

0.0105

0.0110

0.0115

0.0120

11 13 15 17


Rat

e of

pro

gres

s to

flo

wer

ing

(1/f)


A

r2 = 0.99

0.0088

0.0092

0.0096

0.0100

0.0104

0.0108

0.0112

0.0116

0.0120

11 13 15 17


Rat

e of

pro

gres

s to

flo

wer

ing

(1/f)


B


flowering (1/f) of (A) Oriental Poppy cv. Burning Heart and (B) Flax cv. Scarlet

Flax. Each point represents the mean of 6 replicates. Vertical bars on data points

(where larger than the points) represent the standard error within replicates.

r2 = 0.98

0.0124

0.0128

0.0132

0.0136

0.0140

0.0144

0.0148

0.0152

0.0156

0.0160

8 11 14 17


Rat

e of

pro

gres

s to

flo

wer

ing

(1/f)

Zinnia cv. Lilliput

A

r2 = 0.99

0.0124

0.0128

0.0132

0.0136

0.0140

0.0144

0.0148

0.0152

0.0156

0.0160

8 11 14 17


Rat

e of

pro

gres

s to

flo

wer

ing

(1/f)

Sunflower cv. Elf

B


flowering (1/f) of (A) Zinnia cv. Lilliput and (B) Sunflower cv. Elf. Each point


the points) represent the standard error within replicates.

r2 = 0.99

0.0140

0.0144

0.0148

0.0152

0.0156

0.0160

0.0164

0.0168

0.0172

0.0176

8 11 14 17


Rat

e of

pro

gres

s to

flo

wer

ing

(1/f)


A

r2 = 0.95

0.0136

0.0140

0.0144

0.0148

0.0152

0.0156

0.0160

0.0164

0.0168

0.0172

8 11 14 17


Rat

e of

pro

gres

s to

flo

wer

ing

(1/f)


B


progress to flowering (1/f) of (A) French Marigold cv. Orange Gate

and (B) African Marigold cv. Crush. Each point represents the

mean of 6 replicates. Vertical bars on data points (where larger

than the points) represent the standard error within replicates.

r2 = 0.98

0.0098

0.0100

0.0102

0.0104

0.0106

0.0108

0.0110

0.0112

0.0114

0.0116

0.0118

8 11 14 17


Rat

e of

pro

gres

s to

flo

wer

ing

(1/f)


A

r2 = 0.99

0.0110

0.0130

0.0150

0.0170

0.0190

8 11 14 17


Rat

e of

pro

gres

s to

flo

wer

ing

( 1/f

) Cosmos cv. Sonata Pink

B


flowering (1/f) of (A) Cockscomb cv. Bombay and (B) Cosmos cv. Sonata Pink.


larger than the points) represent the standard error within replicates.

0.000

0.002

0.004

0.006

0.008

0.010

0.012

0.014

0.016

0.018

0.000 0.002 0.004 0.006 0.008 0.010 0.012 0.014 0.016 0.018

Actual rate of flowering (d-1)

Pre

dict

ed r

ate

of f

low

erin

g (d

-1)


A

0.000

0.002

0.004

0.006

0.008

0.010

0.012

0.014

0.016

0.018

0.020

0.000 0.002 0.004 0.006 0.008 0.010 0.012 0.014 0.016 0.018 0.020


Pre

dic

ted

rat

e of

flo

wer

ing

(d-1

)


B

Fig 4.2.17(A,B) The relationship between the actual rate of progress to flowering

against those fitted by the flowering model (1 / f = a + bP) for (A) Moss Rose cv.

Sundance and (B) Pansy cv. Baby Bingo grown under 8 (□), 11 (◊), 14 (○) and 17

(Δ) h.d-1 photoperiod. The sold line is the line of identity.

0.000

0.002

0.004

0.006

0.008

0.010

0.012

0.000 0.002 0.004 0.006 0.008 0.010 0.012


Pre

dic

ted

rat

e of

flo

wer

ing

(d-1

)


A

0.000

0.002

0.004

0.006

0.008

0.010

0.012

0.014

0.016

0.018

0.000 0.002 0.004 0.006 0.008 0.010 0.012 0.014 0.016 0.018


Pre

dic

ted

rat

e of

flo

wer

ing

(d-1

)

Petunia cv. Dreams

B


against those fitted by the flowering model (1 / f = a + bP) for (A) Snapdragon cv.

Coronette and (B) Petunia cv. Dreams grown under 8 (□), 11 (◊), 14 (○) and 17 (Δ)

h.d-1 photoperiod. The sold line is the line of identity.

0.000

0.002

0.004

0.006

0.008

0.010

0.012

0.014

0.016

0.018

0.020

0.022

0.000 0.002 0.004 0.006 0.008 0.010 0.012 0.014 0.016 0.018 0.020 0.022


Pre

dic

ted

rat

e of

flo

wer

ing

(d-1

)


A

0.000

0.002

0.004

0.006

0.008

0.010

0.012

0.014

0.016

0.000 0.002 0.004 0.006 0.008 0.010 0.012 0.014 0.016


Pre

dic

ted

rat

e of

flo

wer

ing

(d-1

)


B


against those fitted by the flowering model (1 / f = a + bP) for (A) Annual Verbena

cv. Obsession grown under 8 (□), 11 (◊), 14 (○) and 17 (Δ) h.d-1 photoperiod and

(B) Pot Marigold cv. Resina grown under 11 (□), 13 (◊), 15 (○) and 17 (Δ) h.d-1

photoperiod. The sold line is the line of identity.

0.000

0.002

0.004

0.006

0.008

0.010

0.012

0.014

0.016

0.000 0.002 0.004 0.006 0.008 0.010 0.012 0.014 0.016


Pre

dic

ted

rat

e of

flo

wer

ing

(d-1

)Annual Phlox cv. Astoria Magenta

A

0.000

0.002

0.004

0.006

0.008

0.010

0.012

0.014

0.000 0.002 0.004 0.006 0.008 0.010 0.012 0.014


Pre

dic

ted

rat

e of

flo

wer

ing

(d-1

)


B


against those fitted by the flowering model (1 / f = a + bP) for (A) Annual Phlox

cv. Astoria Magenta and (B) Cornflower cv. Florence Blue grown under 11 (□), 13

(◊), 15 (○) and 17 (Δ) h.d-1 photoperiod. The sold line is the line of identity.

0.000

0.002

0.004

0.006

0.008

0.010

0.012

0.014

0.016

0.000 0.002 0.004 0.006 0.008 0.010 0.012 0.014 0.016


Pre

dic

ted

rat

e of

flo

wer

ing

(d-1

)Oriental Poppy cv. Burning Heart

A

0.000

0.002

0.004

0.006

0.008

0.010

0.012

0.014

0.000 0.002 0.004 0.006 0.008 0.010 0.012 0.014


Pre

dic

ted

rat

e of

flo

wer

ing

(d-1

)


B


against those fitted by the flowering model (1 / f = a + bP) for (A) Oriental Poppy

cv. Burning Heart and (B) Flax cv. Scarlet Flax grown under 11 (□), 13 (◊), 15 (○)

and 17 (Δ) h.d-1 photoperiod. The sold line is the line of identity.

0.000

0.002

0.004

0.006

0.008

0.010

0.012

0.014

0.016

0.018

0.000 0.002 0.004 0.006 0.008 0.010 0.012 0.014 0.016 0.018


Pre

dic

ted

rat

e of

flo

wer

ing

(d-1

)Zinnia cv. Lilliput

A

0.000

0.002

0.004

0.006

0.008

0.010

0.012

0.014

0.016

0.018

0.000 0.002 0.004 0.006 0.008 0.010 0.012 0.014 0.016 0.018


Pre

dic

ted

rat

e of

flo

wer

ing

(d-1

)

Sunflower cv. Elf

B


against those fitted by the flowering model (1 / f = a + bP) for (A) Zinnia cv.

Lilliput and (B) Sunflower cv. Elf grown under 8 (□), 11 (◊), 14 (○) and 17 (Δ) h.d-

1 photoperiod. The sold line is the line of identity.

0.000

0.002

0.004

0.006

0.008

0.010

0.012

0.014

0.016

0.018

0.000 0.002 0.004 0.006 0.008 0.010 0.012 0.014 0.016 0.018


Pre

dic

ted

rat

e of

flo

wer

ing

(d-1

)French Marigold cv. Orange Gate

A

0.000

0.002

0.004

0.006

0.008

0.010

0.012

0.014

0.016

0.018

0.000 0.002 0.004 0.006 0.008 0.010 0.012 0.014 0.016 0.018


Pre

dic

ted

rat

e of

flo

wer

ing

(d-1

)


B


against those fitted by the flowering model (1 / f = a + bP) for (A) French Marigold

cv. Orange Gate and (B) African Marigold cv. Crush grown under 8 (□), 11 (◊), 14

(○) and 17 (Δ) h.d-1 photoperiod. The sold line is the line of identity.

0.000

0.002

0.004

0.006

0.008

0.010

0.012

0.014

0.000 0.002 0.004 0.006 0.008 0.010 0.012 0.014


Pre

dic

ted

rat

e of

flo

wer

ing

(d-1

)Cockscomb cv. Bombay

A

0.000

0.002

0.004

0.006

0.008

0.010

0.012

0.014

0.016

0.018

0.020

0.000 0.002 0.004 0.006 0.008 0.010 0.012 0.014 0.016 0.018 0.020


Pre

dic

ted

rat

e of

flo

wer

ing

(d-1

)


B


against those fitted by the flowering model (1 / f = a + bP) for (A) Cockscomb cv.

Bombay and (B) Cosmos cv. Sonata Pink grown under 8 (□), 11 (◊), 14 (○) and 17

(Δ) h.d-1 photoperiod. The sold line is the line of identity.

4.3 Effects of different light intensities on time to flowering of important ornamental annuals

4.3.1 Introduction

Light is an essential factor in maintaining plants growth and development. The rate

of growth and length of time a plant remains active is dependent on the amount of

light it receives. Light energy is used in photosynthesis, the plant's most basic

metabolic process (Murchie et al., 2002). When determining the effect of light on

plant growth there are three areas to consider: duration, intensity and quality.

Effect of light duration has been studied in the previous experiment (4.2). In this

experiment (4.3) the response of LDPs to light intensities was investigated.

Light intensity is an indication of the strength of a light source. It influences the

photosynthesis, stem length, leaf colour and flowering. Generally, plants grown in

low light tend to be spindly with light green leaves whereas a similar plant grown

in very bright light tends to be shorter, better branches, and have larger, dark green

leaves. Thomas and Vince-Prue (1997) reported that the intensity of illumination

vary from plant to plant such as flowering plants have high light requirements i.e.,

6,000-10,000 lux (74-124µmol.m-2.s-1), flowering bulbs need 500-1,000 lux (6-

12µmol.m-2.s-1) and most foliage plants need from 1,000-6,000 lux (12-74µmol.m-

2.s-1). Similarly, Hildrum and Kristoffersen (1969) found that the plants of

Saintpaulia flowered with light intensities from 5,000 to 13,000 lux (62-

161µmol.m-2.s-1). Post (1942) recommended a light intensity of 10,000 to 15,000

lux (124-186µmol.m-2.s-1) for old flowering plants and 5,000 to 8,000 lux (62-

99µmol.m-2.s-1) for young vegetative plants. However, Cicer arietinum produced

early and more flowers under high light intensity 28 kilolux (347µmol.m-2.s-1) than

the lower 16 kilolux one (198µmol.m-2.s-1) (Sandhu and Hodges, 1971). Karlsson

(2001) reported that light intensity 12 mol·d-1.m-2 (320µmol.m-2.s-1) is more

important than the length of day for cyclamen’s growth, leaf development and rate

of flowering.

By comparing and contrasting the effects of light intensity and photoperiod on an

early (Pink Ice) and a late (Orchid Rocket) flowering cultivar of snapdragon,

Hedley (1974) observed that the increasing light intensity caused a dramatic

reduction in leaf number at flowering in a late flowering cultivar but had no effect

in an early flowering cultivar. The winter snapdragon is an important greenhouse

cut-flower crop but develops slowly during winter due to low light levels (Flint,

1958). The slow growth and development process is also the main limiting factor

in early production. Several approaches have been used to overcome this problem

including the use of new cultivars, raising the glasshouse temperature and using

artificial lighting. A wide range of lighting is available including incandescent,

mercury and fluorescent lamps and high-pressure sodium lamps. Among these,

high-pressure sodium lamps are widely used in out-of-season greenhouse

production systems. Use of artificial lighting during winter enhances flowering

(Laurie and Poesch, 1932; Withrow, 1934; Post and Weddle, 1940). Harte (1974)

suggested that with additional illumination (up to 16h) and a greenhouse

temperature of 20-25°C during winter, two generations of snapdragon could be

grown per year. To further shorten the production cycle, the night temperature

could be raised for plants receiving artificial light at night (Flint, 1958).

Flint and Anderson (1959) found that the various types of lamp used have different

effects such as tungsten filament lamps promoted more rapid flowering but

mercury vapour lamps led to better quality blooms in snapdragon. Similarly,

Whetman (1965) found that incandescent lamps hastened flowering by 3 weeks

and high-pressure mercury vapour lamps by 4 weeks. The effects of these specific

lamps may have been confounded by differences in light intensities as light

intensity has been shown to have a strong effect on flowering time and leaf number

(Cremer et al., 1998). This effect was so significant that in one study, snapdragon

plants at the lowest light intensity (4000 lux) never flowered while at higher light

intensity (30000 lux) plants of inbreds Sippe-50 and S-412 flowered after 110-120

days (Cremer et al., 1998).

The best quality light is natural daylight and wherever possible plants should be

placed under natural source of light for healthy growth. However to extend day

length in winter artificial lighting can be beneficial when natural day length and

light integral decrease. These supplementary lights trigger responses such as

flowering. Major artificial light sources are incandescent lights, fluorescent tubes,

mercury lamps, metal halide lamps, sodium lamps. Light intensity significantly

affects time to flowering in LDPs rather than the SDPs as LDPs are more

responsive to light intensity whereas night break significantly affects the duration

of flowering in SDPs (Thomas and Vince-Prue, 1997). However, in the present

experiment important LD and SD ornamental annuals were selected to study their

flowering time under four different light intensities during winter conditions.


Present research study was carried out at Agricultural Research Institute, Dera

Ismail Khan, Pakistan, during the year 2006 and 2007. Seeds of LDPs such as


Petunia cv. Dreams, Annual Verbena, Pot Marigold cv. Resina, Annual Phlox cv.

Astoria Magenta, Cornflower cv. Florence Blue, Oriental Poppy cv. Burning Heart

and Flax cv. Scarlet Flax and SDPs such as Zinnia cv. Lilliput, Sunflower cv. Elf,

French Marigold cv. Orange Gate, African Marigold cv. Crush, Cockscomb cv.

Bombay, Cosmos cv. Sonata Pink were sown on 1st of October 2005 and 2006 into

module trays containing locally prepared leaf mould compost.



six replicates of each cultivar were shifted to the respective light intensity chamber

i.e., 42µmol.m-2.s-1, 45µmol.m-2.s-1, 92µmol.m-2.s-1 and 119µmol.m-2.s-1.

Supplementary lights were provided by SON-E Eliptical sodium lamp (OSRAM,

Germany) of 50 Watt (42µmol.m-2.s-1), 70 Watt (45µmol.m-2.s-1), 100 Watt

(92µmol.m-2.s-1) and 150 Watt (119µmol.m-2.s-1) for a duration of 8 h (from 08:00

to 16:00h). At 16:00h each day, LDPs were moved into a 17 h photoperiod

chamber whereas SDPs were moved into a blackout chamber where they remained

until 08:00h the following morning. Photoperiod (17 h) within chamber was

extended by two 60Watt tungsten light bulbs and one 18Watt warm white

florescent long-life bulb (Philips, Holland) fixed above 1 m high from the trolleys

providing a light intensity (PPFD) of 7mol m-2 s-1. In this photoperiod chamber,

the lamps were switched on automatically at 1600 h for a further nine hours

duration. These chambers were continuously ventilated with the help of micro

exhaust fan (Fan-0051, SUPERMICRO USA) with an average air speed of 0.2

m.s-1 over the plants when inside the chambers, to minimize any temperature

increase due to heat from the lamps. Temperature and solar radiation were

measured in the weather station situated one kilometer away from the research

venue (Table 4.3.1 and 4.3.2). Temperature was recorded with the help of

Hygrothermograph (NovaLynx Corporation, USA) while solar radiation was

estimated using solarimeters (Casella Measurement, UK).


(3:1 v/v) after 6 leaves emerged. Plants were irrigated by hand and a nutrient

solution [(Premium Liquid Plant Food and Fertilizer (NPK: 8-8-8); Nelson

Products Inc. USA)] was applied twice a week. Plants in each treatment were

observed daily until flower opening (corolla fully opened). Numbers of days to

flowering from emergence were recorded at harvest and the data were analysed

using GenStat-8 (Lawes Agricultural Trust, Rothamsted Experimental Station,

U.K. and VSN International Ltd. U.K.).

Table 4.3.1 Environmental detail of experiment 4.3 (October 1, 2005-2006)


08:00-16:00 Maximum Minimum Average October 2005 33.16 17.13 25.15 8.75 MJ.m-2.d-1 November 2005 26.87 9.53 18.20 7.53 MJ.m-2.d-1 December 2005 22.19 2.90 12.55 7.34 MJ.m-2.d-1 January 2006 20.03 4.10 12.06 7.13 MJ.m-2.d-1 February 2006 26.64 9.00 17.82 7.03 MJ.m-2.d-1

Table 4.3.2 Environmental detail of experiment 4.3 (October 1, 2006-2007)


08:00-16:00 Maximum Minimum Average October 2006 33.61 20.58 27.10 8.53 MJ.m-2.d-1 November 2006 27.43 12.77 20.10 7.48 MJ.m-2.d-1 December 2006 22.10 6.03 14.06 7.42 MJ.m-2.d-1 January 2007 22.35 3.94 13.15 7.39 MJ.m-2.d-1 February 2007 22.25 8.21 15.23 7.49 MJ.m-2.d-1

4.3.3 Results

Results obtained from experiment showed that LDPs such as Moss Rose cv.

Sundance [Fig 4.3.1(A)], Pansy cv. Baby Bingo [Fig 4.3.1(B)], Snapdragon cv.

Coronette [Fig 4.3.2(A)], Petunia cv. Dreams [Fig 4.3.2(B)], Annual Verbena cv.

Obsession [Fig 4.3.3(A)], Pot Marigold cv. Resina [Fig 4.3.3(B)], Annual Phlox

cv. Astoria Magenta [Fig 4.3.4(A)], Cornflower cv. Florence Blue [Fig 4.3.4(B)],

Oriental Poppy cv. Burning Heart [Fig 4.3.5(A)] and Flax cv. Scarlet Flax [Fig

4.3.5(B)] grown under varied light intensities (42, 45, 92 and 119µmol.m-2.s-1)

significantly (P<0.05) affect flowering time. Plants under low irradiance (42 and

45 µmol.m-2.s-1) took more time to flower whereas it decreased significantly when

these plants were raised under high irradiance (119µmol.m-2.s-1). However, there

was non-significant difference between 42 and 45µmol.m-2.s-1 and 92 and

119µmol.m-2.s-1 irradiance regarding days to flowering.

Moss Rose cv. Sundance [Fig 4.3.1(A)] when grown under low irradiance (42 and

45 µmol.m-2.s-1) flowered after 62 and 60 days from emergence, however plants of

same cultivar under high irradiance (92 and 119 µmol.m-2.s-1) flowered after 50

and 43 days. High irradiance reduced flowering time by 19 days. Similarly, Pansy

cv. Baby Bingo [Fig 4.3.1(B)] took 56 (42µmol.m-2.s-1) and 55 (45µmol.m-2.s-1)

days to flower under low light intensity followed by 45 (92µmol.m-2.s-1) and 37

(119µmol.m-2.s-1) days under high light intensity. Plants under low light intensity

took 20 more days to flower as compared to plants received high light intensity.

Twenty-one days difference between low irradiance (88 days, 42µmol.m-2.s-1) and

high irradiance (66 days, 119µmol.m-2.s-1) was recorded in Snapdragon cv.

Coronette [Fig 4.3.2(A)]. Plants received 45µmol.m-2.s-1 light intensity flowered

after 83 days whereas plants grown under 92µmol.m-2.s-1 light level flowered after

73 days. A 16 days late flowering was observed in Petunia cv. Dreams [Fig

4.3.2(B)] when they were grown under low irradiance (60 days, 42µmol.m-2.s-1) as

compared to high light irradiance (44 days, 119µmol.m-2.s-1). Plants grown under

second low irradiance (45µmol.m-2.s-1) took 58 days to flower whereas plants

received second high irradiance took 49 days to flower. Fig 4.3.3(A) depicted that

Annual Verbena cv. Obsession flowered 10 days late under 42µmol.m-2.s-1 (56

days) while plants took 46 days to flower when received 119µmol.m-2.s-1

irradiance. However, time to flowering was 54 days under 45µmol.m-2.s-1 and 48

days under 92µmol.m-2.s-1 irradiance. Pot Marigold cv. Resina [Fig 4.3.3(B)] took

73, 70, 62 and 56 days to flower when grown under 42, 45, 92 and 119µmol.m-2.s-1

light intensities respectively. A 17 days difference was observed between the two

extreme light intensities. Low irradiance (42µmol.m-2.s-1) accelerated flowering

time by 18 days (73 days to flower) in Annual Phlox cv. Astoria Magenta [Fig

4.3.4(A)] as compared to high irradiance (119µmol.m-2.s-1) i.e. 54 days followed

by 12 days under 92µmol.m-2.s-1 (60 days). However, plants took 71 days to flower

when received 45µmol.m-2.s-1 light intensity. Similarly, time to flowering was

increased up to 19 days when Cornflower cv. Florence Blue [Fig 4.3.4(B)] was

grown under 42µmol.m-2.s-1 light intensity (84 days) as compared to 119µmol.m-

2.s-1 treatment (64 days). However, plants took 70 days to flower when grown

under 92µmol.m-2.s-1) light intensity and 80 days when grown under 45µmol.m-2.s-

1 irradiance. Oriental Poppy cv. Burning Heart [Fig 4.3.5(A)] flowered 21 days

later under low irradiance (42µmol.m-2.s-1, 70 days) as compared to high irradiance

(119µmol.m-2.s-1, 49 days). Plants grown under 92µmol.m-2.s-1 light intensity took

54 days to bloom whereas it was 66 days in 45µmol.m-2.s-1 light intensity.

Similarly, 42µmol.m-2.s-1 irradiance (81 days) delayed flowering time up to 16

days in Flax cv. Scarlet Flax [Fig 4.3.5(B)] as compared to 119µmol.m-2.s-1

irradiance (65 days). Plants received 92µmol.m-2.s-1 irradiance flowered after 70

days of emergence whereas in 45µmol.m-2.s-1 light intensity chamber they

flowered after 78 days.




Cosmos cv. Sonata Pink [Fig 4.3.8(B)] was decreased significantly (P<0.05) with

increase in light intensity (42, 45, 92 and 119µmol.m-2.s-1). Plants under low

irradiance (42 and 45µmol.m-2.s-1) took minimum time to flower whereas it

increased significantly under high irradiance levels (92 and 119µmol.m-2.s-1).

However, there was non-significant difference between 42 and 45µmol.m-2.s-1 and

92 and 119µmol.m-2.s-1 irradiance levels regarding days to flowering.

It was observed that Zinnia cv. Lilliput [Fig 4.3.6(A)] flowered 9 days earlier

under low irradiance i.e. 42µmol.m-2.s-1 (61 days) as compared to high irradiance

i.e. 119µmol.m-2.s-1 (70 days). Plants grown under 92µmol.m-2.s-1 flowered after

67 days whereas under 45µmol.m-2.s-1 bloomed after 63 days. In Sunflower cv. Elf

[Fig 4.3.6(B)] a 9 days flowering time difference between 42µmol.m-2.s-1

irradiance (62 days) and 119µmol.m-2.s-1 irradiance (71 days) was observed.

However, plants grown under 92µmol.m-2.s-1 light intensity flowered after 69 days

while 64 days to flower were counted in those plants which received 45µmol.m-2.s-

1 irradiance. French Marigold cv. Orange Gate [Fig 4.3.7(A)] took 57 days to

flower when grown under 42µmol.m-2.s-1 irradiance followed by 59 days in

45µmol.m-2.s-1 irradiance. Similarly, plants grown under high irradiance

(119µmol.m-2.s-1) flowered after 66 days followed by 63 days in 92µmol.m-2.s-1

irradiance. In African Marigold cv. Crush [Fig 4.3.7(B)] plants grown under 42,

45, 92 and 119µmol.m-2.s-1 irradiance took 57, 59, 63 and 66 days to flower

respectively. Again a 9 days difference between two extreme irradiance levels was

observed. Fig 4.3.8(A) showed that Cockscomb cv. Bombay flowered 10 days

earlier when grown under low light intensity i.e. 42µmol.m-2.s-1 (85 days)

irradiance as compared to high light intensity i.e. 119µmol.m-2.s-1 (94 days). Plants

grown in 92µmol.m-2.s-1 irradiance took 91 days to flower whereas in 45µmol.m-

2.s-1 irradiance they took 87 days. Similarly, in Cosmos cv. Sonata Pink [Fig

4.3.8(B)] plants flowered 10 days earlier when grown under low irradiance

(42µmol.m-2.s-1, 52 days) as compared to high irradiance (45µmol.m-2.s-1, 61 days).

Plants grown under 92µmol.m-2.s-1 took 59 days to flower whereas under

45µmol.m-2.s-1 they took 53 days.

Same experiment was repeated in October 1, 2006 to confirm these results and up

to 3 days difference in flowering time was recorded which showed almost the same

pattern as observed in the first year of experiment (October 1, 2005) i.e. a non-



was 0.77ºC and light integrals difference was 0.10 MJ.m-2.d-1.

4.3.4 Discussion

Light duration and irradiance, either independently or in combination have a

critical role in the development of many plant species. The results of previous

experiments (experiments 4.1 and 4.2) showed up to 10 days difference in

flowering time, which was supposed to be difference in days to flowering on

account of different light integrals. Therefore, two experiments were designed to

test flowering behaviour of LDPs and SDPs under artificial (experiment 4.3,

present study) and ambient (experiment 4.4) light integrals.

LDPs such as Moss Rose (19 days), Pansy (20 days), Snapdragon (23 days),

Petunia (16 days), Annual Verbena (10 days), Pot Marigold (17 days), Annual

Phlox (18 days), Cornflower (19 days), Oriental Poppy (21 days) and Flax (16

days) flowered earlier when received 8 hour 119µmol.m-2.s-1 supplementary light.

However, an opposite response of high light irradiance (119µmol.m-2.s-1) was

observed in SDPs (Zinnia, Sunflower, French Marigold, African Marigold,

Cockscomb and Cosmos) i.e. flowering time was increased up to 9-10 days.

LDPs received supplementary irradiance took less time to flower unlike to

experiment 4.1 and 4.2. This indicated that the use of artificial lights could enhance

the rate of progress to flowering, which reduces blossom time. The possible

assumption could be that when there is high irradiance available to the LDPs the

process to produce carbohydrate assimilates (Wiśniewska and Treder, 2003)

becomes rapid therefore plants attain reasonable plant height and apex size

(Hackett and Srinivasani, 1985) in a minimum time to evoke floral stimulus.

Previous work has shown that increased irradiance promotes flower initiation in

the Sinapis alba (LDP) and some changes occurred that are normally observed

during the transition to flowering (full evocation), e.g., elevated soluble sugar and

starch levels, increased numbers of mitochondria and changed nucleolus structure.

These changes are of similar magnitude and follow the same sequence as the

corresponding changes during full evocation (Havelange and Bernier, 1983).

However, Adams et al. (2008) reported that Petunia showed the most dramatic

response to irradiance as dry weight and specific leaf area significantly increased

by low irradiance. At low photosynthetic photon flux densities (PPFD), the

increased leaf area more than compensated for any loss in photosynthetic capacity

per unit leaf area. Shimai (2001) observed that flowering time was significantly

hastened under high irradiance in Petunia. Jadwiga (2003) obtained similar results

and reported that supplementary lighting accelerated flowering time by 3 weeks in

lily cv. Laura Lee during winter which opens an avenue for LDPs to be grown in

winter as well. LDPs are usually grown in winter in countries such as USA,

Netherlands, UK, Canada, Australia, France and Japan for their year-round

production. But in this region the finding of present research can be applied to

grow LDPs during winter season also to have year-round production of these

annuals and to supply these plants in the market at the time of demand. Therefore,

by expanding growing season of LDPs nurserymen or ornamental industry can

reasonably increase their income (Erwin and Warner, 2002). Findings of present

research also open a window to raise LDPs in the northern area during winter as

well. However, in northern area optimum temperature should be maintained for a

successful crop production otherwise slow growth of plant height and leaf

development could affect plant quality (Edwards and Goldenberg, 1976; Armitage

et al., 1981; Ellis et al., 1990; Kaczperski et al., 1991; Pramuk and Runkle, 2003;

Munir et al., 2004; Ushio et al., 2007).

Facultative SDPs such as Zinnia, Sunflower, French and African Marigolds,

Cockscomb and Cosmos can be grown under ambient conditions in summer

(March to September) however they took long time to flower. The duration of

juvenile phase of these plants grown during this season is extended due to long day

length (13-16 h.d-1) and ample light integrals (8.60-10 MJ.m-2.d-1). Present findings

showed that flowering time could be extended up to 10 days if these plants are

grown in winter (their responsive season) under high irradiance (119µmol.m-2.s-1).

The reason why SDPs were less responsive to supplementary lights than the LDPs

could be that the flower initiation in SDPs is usually inhibited by night break

lighting treatments of short duration and low irradiance (flash of red light-660nm)

given near the middle of the night period (Aung 1976). However, interruption of

night by far-red light (730nm) enhanced flowering in SDPs. For example, Hamner

and Bonner (1938) observed that flowering in Xanthium (SDP) could be induced

by a short light interruption in the middle of the night (night break lighting).

Similar results were obtained in other SDPs such as Chenopodium rubrum, Glycine

max and Xanthium strumarium (Thomas and Vince-Prue, 1997). In tomato (SDP)

it was observed that by extending day length or irradiance plants produce more

leaves, increased leaf area and plant dry weight, more branches therefore increase

flowering time (Hurd, 1973). However, Adams et al. (2008) reported that

Impatiens and tomato (SDPs) showed less dramatic increases in dry weight as a

result of LD lighting than Petunia (LDP), but no consistent effects on leaf area or

growth habit were observed. In tomato, increased growth was accompanied by

increased chlorophyll content, but this had no significant effect on photosynthesis.

In both species, increased growth may have been due to a direct effect of LD

lighting on photosynthesis.

r2 = 0.96

424446485052545658606264

42 45 92 119

Light intensities (µmol.m-2.s-1)

Day

s to

flo

wer

ing

SED


A

r2 = 0.97

34363840424446485052545658

42 45 92 119


Day

s to

flo

wer

ing

SED

B


Fig 4.3.1(A,B) Effect of different light intensities on the flowering time of (A)

Moss Rose cv. Sundance and (B) Pansy cv. Baby Bingo. Each point represents the




r2 = 0.99

60

65

70

75

80

85

90

42 45 92 119


Day

s to

flo

wer

ing

SED

A


r2 = 0.97

42

44

46

48

50

52

54

56

58

60

62

42 45 92 119


Day

s to

flo

wer

ing

SED

B

Petunia cv. Dreams

Fig 4.3.2(A,B) Effect of different light intensities on the






r2 = 0.96

42

44

46

48

50

52

54

56

58

42 45 92 119


Day

s to

flo

wer

ing

SED


A

r2 = 0.98

52545658606264666870727476

42 45 92 119


Day

s to

flo

wer

ing

SED

B


Fig 4.3.3(A,B) Effect of different light intensities on the

flowering time of (A) Annual Verbena cv. Obsession and (B) Pot

Marigold cv. Resina. Each point represents the mean of 6




means.

r2 = 0.96

525456586062646668707274

42 45 92 119


Day

s to

flo

wer

ing

SED

A


r2 = 0.96

62646668707274767880828486

42 45 92 119


Day

s to

flo

wer

ing

SED

B







r2 = 0.96

46

50

54

58

62

66

70

74

42 45 92 119


Day

s to

flo

wer

ing

SED

A


r2 = 0.97

626466687072747678808284

42 45 92 119


Day

s to

flo

wer

ing

SED


B






r2 = 0.98

58

60

62

64

66

68

70

72

42 45 92 119


Day

s to

flo

wer

ing

SED

Zinnia cv. Lilliput

A

r2 = 0.98

58

60

62

64

66

68

70

72

42 45 92 119


Day

s to

flo

wer

ing

SED

Sunflower cv. Elf

B


Zinnia cv. Lilliput and (B) Sunflower cv. Elf. Each point represents the mean of 6




r2 = 0.98

54

56

58

60

62

64

66

68

42 45 92 119


Day

s to

flo

wer

ing

SED


A

r2 = 0.99

54

56

58

60

62

64

66

68

42 45 92 119


Day

s to

flo

wer

ing

SED


B


French Marigold cv. Orange Gate and (B) African Marigold cv. Crush. Each point




r2 = 0.99

80

82

84

86

88

90

92

94

96

42 45 92 119


Day

s to

flo

wer

ing

SED


A

r2 = 0.91

50

52

54

56

58

60

62

64

42 45 92 119


Day

s to

flo

wer

ing

SED


B






4.4 Effects of different shade levels (light integrals) on flowering time of important ornamental annuals

4.4.1 Introduction

Light is a critical resource for plants and competition for light under shade can

affect their growth and development. Morphological and physiological responses

of plants to high and low irradiance have been extensively investigated,

constituting one of the classic examples of plasticity (Ballare´ and Scopel. 1997;

Callahan and Pigliucci, 2002; Schmitt et al., 2003). In most of these studies,

irradiance has been reduced with neutral shade, contrasting plants from open

habitats with those from forest shadows. Under natural conditions, however, plants

under leaf canopy experience not only reduction in irradiance but also alter spectral

light quality due to the selective filtering of blue and red wavelengths by

chlorophyll (Schmitt and Wulff, 1993). In particular, the red to far-red ratio (R:FR)

of incident light may be dramatically reduced under the shade as compared with

full sunshine and may also vary widely under different shade levels. Thus R:FR is

an important signal by which plants may detect micro-environmental variation in

shade, both from over the foliage and from neighbours. Similarly, plants grow in

dense stands in non-shaded location use R:FR signal to compete with the

neighbours for light (Vandenbussche et al., 2005). Plant perception of R:FR is

mediated by phytochrome, family of photoreceptors that convert reversibly

between two forms when exposed to red or far-red light (Smith, 2000). It has been

reported that the primary function of phytochrome is to act as a sensitive sensor of

shade. Phytochrome-mediated morphogenesis in light grown plants is a function of

the photoequilibrium between the two forms, resulting in a sensitive, graded

morphological response to light quality over the range of R:FR values typical of

vegetation shade (Schmitt and Wulff, 1993).

When plants are shaded, two types of reactions can occur. Shade-acclimation

responses maximize light harvesting in shade conditions through increases in

specific leaf area and reduced chlorophyll a:b ratio (Evans and Poorter, 2001),

whereas shade-avoidance responses maximize light capture by positioning the

leaves out of the shade (Ballare´, 1999). Shade-avoiding plants have machinery

that reacts quickly to changes in R:FR ratio that are sensed by the phytochrome

(Franklin and Whitelam, 2005). Many plant species typically respond to reduction

in the R:FR of incident light with increased apical dominance, reduced branching,

the upward orientation of leaves (hyponasty), stem extension and internode

elongation. In the long term, low R:FR exposure leads to early flowering (Cerda´

and Chory, 2003) and seed set, which is considered to be an escape mechanism

because it shortens generation time. These responses constitute the adaptive

plasticity of plants to shading (Schmitt et al., 1995). Recently, shade-avoidance

responses were considered predominantly as a function of R:FR ratio. Evidence is

accumulating, however, that plants also adjust growth to diminishing light

intensities, including that of blue light (Pierik et al., 2004). Light intensity affects

chloroplast positioning, allowing optimal light harvesting. Thus, photoreceptors

serve not only as quality detectors but also as photon counters. Recent advances in

understanding the molecular mechanisms of shade-avoidance responses have

unveiled interactions between light signalling and the circadian clock, and have

revealed a more profound view of the hormonal pathways that are involved

(Ballare´, 1999).

These studies indicated that manipulating light integrals could control plant growth

and development. Hence, an assumption appears that flowering process is slow

down if long day plants (LDPs) are grown under low light integrals and vice versa.

However, an opposite assumption can be made for short day plants (SDPs) i.e.

flowering process is accelerated if SDPs are grown under low light integrals and

vice versa. To test these assumptions an experiment was designed to grow various

LDPs and SDPs under different light levels (shades) to observe their flowering

response under the ecological conditions of Dera Ismail Khan.


Present research study was carried out in Agricultural Research Institute, Dera

Ismail Khan, Pakistan, during the year 2006 and 2007. Seeds of LDPs such as


Petunia cv. Dreams, Annual Verbena, Pot Marigold cv. Resina, Annual Phlox cv.

Astoria Magenta, Cornflower cv. Florence Blue, Oriental Poppy cv. Burning Heart

and Flax cv. Scarlet Flax were sown on 1st of March 2006 and 2007 into module

trays containing locally prepared leaf mould compost. Similarly, seeds of SDPs

such as Zinnia cv. Lilliput, Sunflower cv. Elf, French Marigold cv. Orange Gate,

African Marigold cv. Crush, Cockscomb cv. Bombay, Cosmos cv. Sonata Pink

were sown on 1st of September 2006 and 2007. The reason of planting LDPs in

March (long day length) and SDPs in September (short day length) was to estimate

flowering character under their respective responsive environment.

Seed trays were kept at room temperature at night and were moved out during the

day (08:00–16:00 h) under partially shaded area. After 70% seed germination, six

replicates of each cultivar were shifted to the trolleys of respective shade levels

i.e., 0% (control), 20%, 30% and 40%. LDPs grown under 0, 20, 30 and 40%

shades received 9.34, 7.47, 6.54 and 5.60 MJ.m-2.d-1 light integrals respectively

until flowering. Similarly, SDPs grown under same shade levels received 7.53,

6.02, 5.27 and 4.52 MJ.m-2.d-1 light integrals respectively until flowering. Plants

remained outside in the research area until completion of the experiment under

ambient daylight and temperature (Table 4.4.1 and 4.4.2). Temperature and solar

radiation were measured in the weather station situated one kilometer away from

the research venue. Temperature was recorded with the help of Hygrothermograph

(NovaLynx Corporation, USA) while solar radiation was estimated using

solarimeters (Casella Measurement, UK). Shade levels inside the covered trolleys

were measured using the light meter quantum sensor (LI-189, LI-COR

Biosciences, USA).


(3:1 v/v) after 6 leaves emerged. Plants were irrigated by hand and a nutrient

solution [(Premium Liquid Plant Food and Fertilizer (NPK: 8-8-8); Nelson

Products Inc. USA)] was applied twice a week. Plants in each treatment were

observed daily until flower opening (corolla fully opened). Numbers of days to

flowering from emergence were recorded at harvest and the data were analysed

using GenStat-8 (Lawes Agricultural Trust, Rothamsted Experimental Station,

U.K. and VSN International Ltd. U.K.).

Table 4.4.1 Environmental detail of experiment 4.4 (Year 2006).

Growing Season Diurnal temperature (C) Light integral

MJ.m-2.d-1 Day length

(h.d-1) Maximum Minimum Average

LDPs

March 2006 26.94 12.71 19.82 8.20 13.30 April 2006 36.23 18.47 27.35 9.67 14.21 May 2006 41.87 25.45 33.66 9.64 15.40June 2006 41.33 25.37 33.35 9.86 16.16

SDPs

September 2006 37.53 23.97 30.75 6.69 14.25 October 2006 33.61 20.58 27.10 8.53 13.12 November 2006 26.50 12.77 19.63 7.48 12.39 December 2006 23.26 6.03 14.65 7.42 12.15

Table 4.4.2 Environmental detail of experiment 4.4 (Year 2007).

Growing Season

Diurnal temperature (C) Light integral

MJ.m-2.d-1 Day length

(h.d-1) Maximum

Minimum Average

LDPs

March 2007 25.84 13.10 19.47 8.63 13.30 April 2007 38.73 18.53 28.63 9.87 14.21 May 2007 41.58 23.26 32.42 9.87 15.40 June 2007 41.33 27.47 34.40 10.12 16.16

SDPs

September 2007 36.53 23.10 29.82 9.69 14.25 October 2007 34.16 15.39 24.77 8.64 13.12 November 2007 27.27 11.03 19.15 7.74 12.39 December 2007 21.61 4.52 13.06 7.58 12.15

4.4.3 Results

The results of present experiment revealed a statistically significant (P<0.05)

difference between shade levels regarding flowering time in LDPs such as Moss

Rose cv. Sundance [Fig 4.4.1(A)], Pansy cv. Baby Bingo [Fig 4.4.1(B)],

Snapdragon cv. Coronette [Fig 4.4.2(A)], Petunia cv. Dreams [Fig 4.4.2(B)],

Annual Verbena cv. Obsession [Fig 4.4.3(A)], Pot Marigold cv. Resina [Fig

4.4.3(B)], Annual Phlox cv. Astoria Magenta [Fig 4.4.4(A)], Cornflower cv.

Florence Blue [Fig 4.4.4(B)], Oriental Poppy cv. Burning Heart [Fig 4.4.5(A)] and

Flax cv. Scarlet Flax [Fig 4.4.5(B)]. Plants under low irradiance (high shade level)

took more time to flower whereas it decreased significantly under lower shade

levels and control.

Moss Rose cv. Sundance [Fig 4.4.1(A)] flowered 21 days later under 40% shade

(75 days) followed by 14 days under 30% shade (68 days) and 6 days under 20%

shade (60 days) as compared to control (54 days). Similarly, Pansy cv. Baby Bingo

[Fig 4.4.1(B)] took 24 more days to flower under 40% shade (73 days) followed by

14 days under 30% shade (64 days) and 8 days under 20% shade (58 days) when

compared with control plants (49 days). Thirty-one days difference between low

irradiance (40% shade, 119 days) and control (88 days) was recorded in

Snapdragon cv. Coronette [Fig 4.4.2(A)] followed by 22 days difference under

30% (110 days) and 8 days under 20% shade (96 days). A 23 days late flowering

was observed in Petunia cv. Dreams [Fig 4.4.2(B)] when they were grown under

40% shade (81 days) as compared to control (57 days). However, this difference

was decreased up to 15 days under 30% shade (72 days) followed by 7 days under

20% shade (65 days) when compared with control. Fig 4.4.3(A) depicted that

Annual Verbena cv. Obsession flowered 17 days later under 40% shade (65 days)

followed by 10 days under 30% (58 days) and 5 days under 20% (53 days) shade

as compared to control (49 days). Similarly, 23 days late flowering was observed

when Pot Marigold cv. Resina [Fig 4.4.3(B)] was grown under 40% shade (95

days) as compared to control (71 days). Plants under 30% (85 days) and 20% (80

days) shades flowered 14 and 9 days later as compared to control. Low irradiance

i.e. 40% shade accelerate flowering time by 24 days (95 days to flower) in Annual

Phlox cv. Astoria Magenta [Fig 4.4.4(A)] as compared to control (71 day) followed

by 17 days under 30% (88 days) 8 days under 20% (79 days) shade. Similarly, time

to flowering was increased up to 22 days when Cornflower cv. Florence Blue [Fig

4.4.4(B)] was grown under 40% shade (101 days) as compared to control (79 days)

followed by 11 days under 30% (90 days) and 8 days under 20% (88 days) shade

treatments. Oriental Poppy cv. Burning Heart [Fig 4.4.5(A)] flowered 31 days later

under 40% shade (97 days) as compared to control (66 days) followed by 22 days

under 30% (88 days) and 10 days under 20% (76 days) shade. Similarly, 40%

shade (103 days) delayed flowering time up to 20 days in Flax cv. Scarlet Flax [Fig

4.4.5(B)] as compared to control (83 days) whereas 13 days difference was

observed in 30% shade (96 days) followed by 6 days in 20% shade (88 days).




Cosmos cv. Sonata Pink [Fig 4.4.8(B)] was decreased significantly (P<0.05) with

increase in shade levels (0-40%). Plants under low irradiance (high shade level)

took less time to flower whereas it increased significantly under lower shade levels

and control.

It was observed that Zinnia cv. Lilliput [Fig 4.4.6(A)] flowered 10 days earlier

under low irradiance i.e. 40% shade (62 days) as compared to control (72 days)

followed by 8 and 3 days earlier flowering under 30% (64 days) and 20% shade

(69 days) respectively. Similarly, as shown in Fig 4.4.6(B) 10 days flowering time

difference between 40% shade (62 days) and control (72 days) while 8 and 4 days

early flowering was noted in plants grown under 30% (65 days) and 20% shade (69

days) respectively in Sunflower cv. Elf. French Marigold cv. Orange Gate [Fig

4.4.7(A)] flowered 11 days early under 40% low light integrals i.e. 40% shade (61

days) as compared to control (72 days) followed by 8 and 5 days earlier flowering

under 30% (64 days) and 20% (67 days) shade levels. Similarly, in African

Marigold cv. Crush [Fig 4.4.7(B)] 8, 6 and 2 days earlier flowering was recorded

in plants grown under 40% (60 days), 30% (63 days) and 20% (66 days) shade

levels as compared to control treatment (69 days). Fig 4.4.8(A) depicted that

Cockscomb cv. Bombay flowered 11 days earlier when grown under low light

integrals i.e. 40% shade (86 days) as compared to control plants (97 days) followed

by 7 and 3 days early flowering under 30% (90 days) and 20% (94 days) shade

levels. Similarly, Fig 4.4.8(B) indicated that Cosmos cv. Sonata Pink when grown

under low irradiance flowered 9 days earlier (40% shade took 52 day to flower) as

compared to control plants (61 days) under high irradiance. Plants grown under

30% (56 days) and 20% (59 days) shade levels flowered 5 and 2 days earlier

respectively as compared to control.

Same experiment was repeated in 2007 to confirm these results and up to 5 days

difference in flowering time was recorded which showed almost the same pattern

as observed in the first year of experiment (2006) i.e. a non-significant difference

between the two years data. This is because of the least difference between the two

years ambient environment i.e. temperature difference was 0.18-1.32ºC and light

integrals difference was 0.28-0.88 MJ.m-2.d-1.

4.4.4 Discussion

Previous studies (Experiments 4.1 and 4.2) indicated that there is 10-15 days

difference in time to flowering when ornamental annuals (LDPs and SDPs) were

grown in ambient day length (Experiments 4.1) and in controlled photoperiods

(Experiments 4.2). The results of these studies established an assumption that the

difference in flowering time was due to the difference in light integrals. As the

light integrals were higher in ambient day length experiment therefore ornamental

annuals bloomed 10-15 days earlier (LDPs) or late (SDPs) than the controlled

photoperiod experiment (low light integrals). Two experiments were designed to

test this hypothesis. First experiment was conducted under artificial source of light

integrals (light intensities using the SON-E Eliptical sodium lamp, Experiment 4.3)

whereas another experiment was conducted under natural light integrals (shade

experiment). Results obtained from first experiment showed a difference between

different light intensities. The results of second experiment (present study) also

showed a significant difference among days to flowering in LDPs and SDPs.

LDPs grown under low light integrals (5.60, 6.54, and 7.47 MJ.m-2.d-1 i.e. 40, 30

and 20% shade, respectively) were etiolated because R:FR ratio of incident light

reduced under the shade (Schmitt et al., 2003) which subsequently delayed

flowering time (Cerdá and Chory, 2003). This indicated that LDPs made efforts to

capture sufficient sunlight (enriched in far red light) for their growth and

development. In present study LDPs received around 16 h.d-1 ambient day length

therefore it was only shade that interrupts light integrals and affect flowering time

(Callahan and Pigliucci, 2002). Consequently, LDPs could not capture enough

light to perceive signal from leaf (O’Neil, 1992) to the apex (McDaniel, 1996)

therefore flower induction process significantly delayed under low light integrals.

Typically, such a response results in an increase in apical dominance and in stem

growth as a result of internode elongation (Davies et al., 2002). It has been

observed in the present experiment that low light integrals (40% shade or 5.60

MJ.m-2.d-1) reduced the ability of stem to stand erect without bending. Similarly,

Shikanori and Hiroshi (2000) reported that low irradiance delayed flowering,

reduced flowering rate and increased the leaves size in amaryllis. Findings of this

research revealed that LDPs such as Snapdragon, Petunia, Cornflower, Oriental

Poppy and Flax which are normally produced terminal flower, induced lateral

floral buds when grown under low light integrals (40% shade or 5.60 MJ.m-2.d-1).

This indicated that these plants should not be kept longer under intense shade after

juvenile phase otherwise the quality of these plants is affected (Dana et al., 1980).

A quite opposite response was observed in SDPs where flowering time was

reduced significantly when light integrals were reduced (4.52, 5.27 and 6.02 MJ.m-

2.d-1 i.e. 40, 30 and 20% shade, respectively). The reason is in fact long nights

accelerate flowering process in SPDs as phytochrome reversion appears to be

coupled into a time-measuring reaction of some kind, when this is completed

hormone synthesis begins in the leaves and continues throughout the remainder of

the night which sends a signal to apex to induce flowering (Thomas and Vince-

Prue, 1997). In present study when SDPs attained an appropriate apex size then

they were competent to induce flowering earlier than the other treatments under

low light integrals.

r2 = 0.99

50

54

58

62

66

70

74

78

0% 20% 30% 40%

Shade levels

Day

s to

flo

wer

ing

SED


A

r2 = 0.99

48

52

56

60

64

68

72

76

0% 20% 30% 40%

Shade levels

Day

s to

flo

wer

ing

SED

B


Fig 4.4.1(A,B) Effect of different shade levels on the flowering time of (A) Moss

Rose cv. Sundance and (B) Pansy cv. Baby Bingo. Each point represents the mean

of 6 replicates. Vertical bars on data points (where larger than the points) represent

the standard error within replicates whereas vertical bar (SED) showing standard

error of difference among means.

r2 = 0.99

86

90

94

98

102

106

110

114

118

122

0% 20% 30% 40%

Shade levels

Day

s to

flo

wer

ing

SED

A


r2 = 0.99

54

58

62

66

70

74

78

82

0% 20% 30% 40%

Shade levels

Day

s to

flo

wer

ing

SED

B

Petunia cv. Dreams

Fig 4.4.2(A,B) Effect of different shade levels on the flowering

time of (A) Snapdragon cv. Coronette and (B) Petunia cv. Dreams.

Each point represents the mean of 6 replicates. Vertical bars on

data points (where larger than the points) represent the standard

error within replicates whereas vertical bar (SED) showing


r2 = 0.99

46

4850

5254

5658

6062

6466

68

0% 20% 30% 40%

Shade levels

Day

s to

flo

wer

ing

SED

A


r2 = 0.98

70

74

78

82

86

90

94

98

0% 20% 30% 40%

Shade levels

Day

s to

flo

wer

ing

SED

B


Fig 4.4.3(A,B) Effect of different shade levels on the flowering

time of (A) Annual Verbena cv. Obsession and (B) Pot Marigold

cv. Resina. Each point represents the mean of 6 replicates. Vertical

bars on data points (where larger than the points) represent the

standard error within replicates whereas vertical bar (SED)

showing standard error of difference among means.

r2 = 0.99

68

72

76

80

84

88

92

96

100

0% 20% 30% 40%

Shade levels

Day

s to

flo

wer

ing

SED

A


r2 = 0.95

76

80

84

88

92

96

100

104

0% 20% 30% 40%

Shade levels

Day

s to

flo

wer

ing

SED

B


Fig 4.4.4(A,B) Effect of different shade levels on the flowering time of (A)





r2 = 0.99

64

68

72

76

80

84

88

92

96

100

0% 20% 30% 40%

Shade levels

Day

s to

flo

wer

ing

SED

A


r2 = 0.99

80828486889092949698

100102104106

0% 20% 30% 40%

Shade levels

Day

s to

flo

wer

ing

SED

B







r2 = 0.98

60

62

64

66

68

70

72

74

0% 20% 30% 40%

Shade levels

Day

s to

flo

wer

ing

SED

A

Zinnia cv. Lilliput

r2 = 0.98

60

62

64

66

68

70

72

74

0% 20% 30% 40%

Shade levels

Day

s to

flo

wer

ing

SED

B

Sunflower cv. Elf

Fig 4.4.6(A,B) Effect of different shade levels on the flowering time of (A) Zinnia

cv. Lilliput and (B) Sunflower cv. Elf. Each point represents the mean of 6




r2 = 0.99

58

60

62

64

66

68

70

72

74

0% 20% 30% 40%

Shade levels

Day

s to

flo

wer

ing

SED

A


r2 = 0.98

58

60

62

64

66

68

70

0% 20% 30% 40%

Shade levels

Day

s to

flo

wer

ing

SED

B


Fig 4.4.7(A,B) Effect of different shade levels on the flowering time of (A) French

Marigold cv. Orange Gate and (B) African Marigold cv. Crush. Each point




r2 = 0.99

84

86

88

90

92

94

96

98

100

0% 20% 30% 40%

Shade levels

Day

s to

flo

wer

ing

SED

A


r2 = 0.97

50

52

54

56

58

60

62

64

0% 20% 30% 40%

Shade levels

Day

s to

flo

wer

ing

SED

B







4.5 An appraisal of the use of reciprocal transfer experiments: Assessing the stages of photoperiod sensitivity in Pansy, Snapdragon, Petunia and Cosmos

4.5.1 Introduction

In previous experiments, the effects of ambient day length, photoperiod, and light

intensity on flowering time were determined. The results obtained from these

experiments illustrates how these environmental factors affect flowering process

but these experiments did not show whether any of the annual ornamental is

sensitive or insensitive to photoperiod. In present trial a reciprocal transfer

experiment is designed to examine photoperiod sensitivity in three LDPs (Pansy,

Petunia, Snapdragon) and one SDP (Cosmos) using a novel statistical model.

Plants pass through distinct photoperiod-sensitive/insensitive phases during

development. The duration of these phases can be determined using reciprocal

transfers where plants are moved between inductive and non-inductive

photoperiods at regular intervals until flower opening (Roberts et al., 1986). Many

researchers have used this technique with a range of plants including maize, barley,

soybean, Arabidopsis, opium poppy, chrysanthemum, petunia and Antirrhinum

(Kiniry et al., 1983; Roberts et al., 1988; Wilkerson et al., 1989; Mozley and

Thomas, 1995; Wang et al., 1997a,b; Adams et al., 1998a, 1999; Munir, 2003).

A number of studies have shown that the early (juvenile) and late (flower

development) phases of growth are insensitive to photoperiod (Roberts et al., 1986;

Collinson et al., 1992; Ellis et al., 1992). Maginnes and Langhans (1960 and 1961)

demonstrated that Antirrhinum is a quantitative LDP and its sensitivity to

photoperiod is confined to a critical phase in plant development. This critical phase

was defined (for all cultivars) as the period of growth from 40 to 65 days following

germination or the 5-10 leaf pair stage of development (Langhans and Maginnes,

1962). Long days given before this critical phase did not promote flowering and

after the critical phase flowering could occur in other long or short days. However,

Hedley (1974) carried out experiments on ‘Pink Ice’ and ‘Orchid Rocket’ and

concluded that under a high light intensity both cultivars became sensitive to

photoperiod 22 days after germination. While differing slightly, these findings do

however, clearly show that photoperiod does not influence flowering over the

entire period from germination to flower bud initiation, but rather during a definite

period just after the juvenile phase and prior to flower bud initiation. This

photoperiod-sensitive stage has also been referred to as the inductive phase

(Maginnes and Langhans, 1961; Rabinowitch et al., 1976). However, Adams et al.

(1998a) reported that the cuttings of chrysanthemum, a SDP, were sensitive to

photoperiod from the first transfer, 4 days after pinching under high light integral

conditions. They also reported that the same specie was sensitive at pinching but

needed a period of inductive cycles when grown under a lower light integral.

Some studies have shown that temperature can affect the length of the juvenile and

flower development phases (Collinson et al., 1992), others (Adams et al., 1999)

have reported that the juvenile phase is much more affected by light integral than

temperature. Clearly this may be due to species differences and so demands further

investigation. The experiments described previously indicated significantly earlier

flowering in response to long ambient day length, photoperiods, and increased light

intensity. However, it has also been reported that some annual ornamentals are not

influenced by photoperiod before a ‘critical phase’, the duration of which varied

from cultivar to cultivar (Langhans and Maginnes, 1962; Hedley, 1974, Adams et

al., 1998a, 1999; Munir, 2003). Therefore, an attempt has been made to study

photoperiod sensitivity of three LDPs (Pansy cv. Baby Bingo, Petunia cv. Dreams,

Snapdragon cv. Coronette) and one SDP (Cosmos cv. Sonata Pink) to quantify the

duration of flower development phases using Adams et al. (2003) analytical

approach.

4.5.1.1 Analytical approach presented by Ellis et al. (1992)

In 1992, Ellis and co-workers introduced a holistic approach to analyse data of

reciprocal transfer experiments to quantify the effects of different treatments by as

few parameters as possible. By using this method they quantified the effect of the

different times from sowing to transfer (tc), both from SD to LD and from LD to

SD, on duration from sowing to flowering (f) by only four parameters: the duration

of the pre-inductive phase (a1); the duration of the inductive phase in SD (IS); the

duration of the inductive phase in LD (IL); and the duration of the post-inductive

phase (a3). The schematic representation of this model is shown in Figure 4.5.1.

Figure 4.5.1 indicates that number of days taken from sowing to first flowering in

continuous SD could be counted control as

f = a1 + IS + a3 4.5.1

while in the LD control

f = a1 + IL + a3 4.5.2

IS

a1 IL

Figure 4.5.1 Schematic representation (not to scale) of the response of time from

seedling emergence to first flowering (f) for a LDP transferred from LD to SD

(────) and from SD to LD (--------) at various times from sowing if the period

from sowing to first flowering comprises a photoperiod-sensitive phase (durations

IL and IS in long- and short-days, respectively) sandwiched between two

photoperiod-insensitive phases, namely a pre-inductive phase (duration a1) and a

post-inductive phase (duration a3).

Equation 4.5.1 also applies for plants transferred from LD to SD where tc ≤ a1 and

for those transferred from SD to LD where tc ≥ a1 + IS, where equation 4.5.2 also

applies for the SD to LD transfer treatments where tc ≤ a1 and for the LD to SD

transfer treatments where tc ≥ a1 + IL (Figure 4.5.1).

Day

s to

flo

wer

(f)

a1 + IS + a3

a1 + IL + a3

Days of transfer (tc)

Assuming that a negative linear relation between the rate of progress to flowering

(1 / f) and photoperiod (P) within the appropriate range of photoperiods applies

during the inductive phase of length I d, then, for SDPs:

1 / I = a2 – cP 4.5.3

in which a2 and c are constants for the cultivar and the latter is proportional to its

photoperiod sensitivity.

Now, consider plants transferred from SD to LD during the inductive phase. Let

the number of days that plants are exposed to P1 during the inductive phase be I1,

and the number of days at P2 during the inductive phase be I2, where P1 and P2 are

the photoperiods in the SD and LD regimes, respectively. Consequently, the

fractional progress through the inductive phase is (a2 – cP1) I1 in SD and

subsequently (a2 –cP2) I2 in LD, where (a2 – cP1) I1 + (a2 – cP2) I2 = 1

4.5.4

and, by definition, the duration of the inductive phase is I1 + I2. Now, from

equation 4.4.3 IL = 1 / (a2 – cP2) and IS = 1 / (a2 – cP1), and so equation can be

re-written as I1 / IS + I2 / IL = 1

4.5.5

and hence I2 can be defined as follows

I2 = IL – I1 IL / IS 4.5.6

A simpler algebraic derivation of equation 4.5.5 is to say that the rate of progress

through the inductive phase is 1 / IS d-1 in PS and 1 / IL d-1 in PL; the fractional

progress accumulated in each photoperiod is thus I1 / IS and I2 / IL, respectively.

Since I1 = tc – a1, I1 in equation 4.5.6 can be replaced by the latter term to give

I2 = IL – (tc – a1) IL / IS 4.5.7

and because by definition f = a1 + I1 + I2 + a3 and I1 = tc – a1 it follows that

f = a1 + tc – a1 + IL – (tc – a1) IL / IS + a3 4.5.8

which simplifies to

f = tc + IL – (tc – a1) IL / IS + a3 4.5.9

Similar logic for the transfers from LD to SD gives

f = tc + IS – (tc – a1) IS / IL + a3 4.5.10

In summery then, for transfers from LD to SD;

f = a1 + IS + a3 when tc ≤ a1 (including the SD control, i.e. tc = 0),

f = tc + IS – (tc – a1) IS / IL + a3 when a1 < tc < a1 + IL, while

f = a1 + IL + a3 when tc ≥ a1 + IL

Similarly, for transfer from SD to LD

f = a1 + IL + a3 when tc ≤ a1 (including the LD control, i.e. tc = 0),

f = tc + IL – (tc – a1) IL / IS + a3 when a1 < tc < a1 + IS, and finally

f = a1 + IS + a3 when tc ≥ a1 + IS

Thus, it is possible to quantify the results of all treatments of reciprocal transfer

experiment by just the four parameters a1, IS, IL, and a3.

4.5.1.2 Analytical approach presented by Adams et al. (2003)

Estimating the phases of photoperiod sensitivity by analysing the flowering time

response: As stated earlier, Ellis et al. (1992) developed a method of analysing the

results of reciprocal transfer experiments using four parameters; a1 (the

photoperiod-insensitive pre-inductive phase), IS and IL (the photoperiod-sensitive

inductive phase in SD and LD), and a3 (the photoperiod-insensitive post-inductive

phase in LD and SD). The analytical approach presented by Ellis et al. (1992)

assumes that at the end of the photoperiod-insensitive, pre-inductive (juvenile)

phase an immediate change in time to flowering will be seen in plants transferred

from both inductive to non-inductive and non-inductive to inductive conditions for

flowering. However, it has been shown that this approach does not consider any

time lag from the onset of photoperiod sensitivity before an effect of photoperiod

on the time to flowering can be observed in plants transferred from an inductive to

a non-inductive environment (Adams et al., 1998). The duration of this phase,

which can be determined provided a short transfer interval is used, coincides with

the number of inductive cycles needed for flower commitment. It has also been

reported in a LDP (opium poppy) that minimum number of inductive cycles for

flowering can be separated from the duration of the juvenile phase (Wang et al.,

1997). Therefore, the analytical approach presented by Ellis et al. (1992) can

confound the effects of juvenility with the number of inductive cycles required for

flower commitment after plants become sensitive to photoperiod, and so may be

inaccurate where a large number of cycles are required for flower commitment.

Therefore, Adams et al. (1999, 2001) separated the effects of photoperiod on

flower induction and development, hence re-labelled the photoperiod sensitive

phase in LD (IL) as PI + Pd (photoperiod sensitive flower induction (PI) and flower

development (Pd) phases).

As these models analyse only flowering time data, however, recently Adams and

co-workers have introduced a new model which analyse flowering time and leaf

number simultaneously and quantify both time to flowering and leaf number at

various photoperiod-sensitive and insensitive phases (Adams et al., 2003). The

modified schematic representation of this model for LDP is shown in Figure

4.5.2(A,B).

Figure 4.5.2(A) assumes that the number of days to first flower (f) from emergence

in continuous LD can be quantified as:

f = a1 + PIL + PdL + a3 4.5.11

This applies when plants are transferred from SD to LD before the end of photo-

insensitive juvenile phase (a1), when the day of transfer (tc) from SD to LD ≤ a1 or

for plants transferred from LD to SD while in the photo-insensitive flower

development phase (a3) which means that tc ≥ a1 + PIL + PdL.

In a similar way, time to flowering (f) in continuous SD for LDP can be estimated

as:

f = a1 + PIS + PdS + a3 4.5.12

This applies when plants are transferred from LD to SD before the end of the

photoperiod-sensitive flower induction phase (PIL), when tc ≤ a1 + PIL or if plants

are transferred from SD to LD during the photoperiod-insensitive flower

development phase (a3) i.e. tc ≥ a1 + PIS + PdS. Similar to the analytical approach

reported by Ellis et al. (1992), the time to first flower when plants are transferred

from LD to SD during the photoperiod-sensitive flower development phase (PdL)

(a1 + PIL ≤ tc ≤ a1 + PIL + PdL), can be estimated as:

f = tc + PIS + PdS – [(tc – a1 – PIL) (PIS + PdS – PIL) / PdL] + a3 - PIL 4.5.13

PdL

a1 + PIL

a1 PIS + PdS

a1 + PIL

a1 PIS

Figure 4.5.2(A,B) Schematic representation (not to scale) of the model for a LDP

transferred from LD to SD (────) and from SD to LD (--------) at regular

intervals from seedling emergence to first flowering. The response of the plants

being described by five developmental phases, a photoperiod-insensitive juvenile

Day

s to

flo

wer

(f)

a1 + PIS + PdS + a3

a1 + PIL + PdL + a3

A

B


Ls

LL

Lea

f n

um

ber


phase (a1), photoperiod-sensitive flower induction (PIL) and flower development

(PdL) phases in LD, a photoperiod-sensitive phase for flowering in SD (PIS) and a

photoperiod-insensitive flower development (a3) phase (from Adams et al., 2003).

Similarly when plants are transferred from SD to LD during the photoperiod-

sensitive inductive phase in SD (IS) when a1 ≤ tc ≤ a1 + PIS +PdS, the time to first

flower time can be estimated as:

f = tc + PdL – [(tc – a1) (PdL + PIL) / (PIS + PdS)] + a3 + PIL 4.5.14

Estimating the phases of photoperiod sensitivity by analysing the leaf numbers: It

is possible to indicate the phases of photoperiod sensitivity by counting leaf

numbers below the inflorescence in annual ornamentals, which produce a terminal

inflorescence [4.5.2(B)]. A model presented by Adams et al. (2003) allows us to

quantify these phases by counting the leaf numbers at each phase. This approach

considers three phases: a1, the photoperiod-insensitive juvenile phase; PIL and PIS,

the photoperiod-sensitive induction phases in LD and SD, respectively. All theses

three parameters are same as mentioned in the above flowering model.

Plants produce the same leaf numbers in continuous LD (LL) and plants transferred

from SD to LD before the end of juvenile phase (a1), tc ≤ a1, or plants transferred

from LD to SD after the commitment of flower (tc ≥ a1 + PIL). Similarly, the leaf

numbers produced under continuous SD (LS) will be the same as the leaf numbers

of plants transferred from LD to SD before flower commitment (tc ≤ a1 + PIL), or

when plants are transferred from SD to LD after flower commitment under SD (tc

≥ a1 + PIS). When plants are transferred from SD to LD during the photoperiod-

sensitive flower inductive phase in SD (PIS) i.e. a1 ≤ tc ≤ a1 + PIS, the leaf numbers

can be estimated as below:

L = LL + (LS – LL) [(tc – a1) / PIS] 4.5.15

All this shows that the duration of photo-sensitive/insensitive phases can be

calculated using the five equations above i.e. 4.5.11 to 4.5.15 (Adams et al., 2003).


This piece of work was carried out at Agricultural Research Institute, Dera Ismail

Khan, Pakistan during the year 2006 and 2007. Seeds of Pansy cv. Baby Bingo,

Snapdragon cv. Coronette, Petunia cv. Dreams and Cosmos cv. Sonata Pink were

sown on 15th of June 2006 into seed trays which were kept at room temperature at

night and they were moved out during the day (08:00–16:00 h) under partially

shaded area. After 70% seed germination, plants were potted into 9cm pots

containing leaf mould compost and river sand (3:1 v/v). These seedlings were then

transferred to the LD (17 h.d-1) and SD (8 h.d-1) photoperiods chambers. Plants

remained for 8h (from 08:00 to 16:00h) in the field (outside the photoperiod

chambers) where they were exposed to natural daylight and temperature (Table

4.5.1 and 4.5.2). At 16:00h each day, all plants were moved into the photoperiod

chambers where they remained until 08:00h the following morning. Photoperiod

within each of the chambers was extended by two 60Watt tungsten light bulbs and

one 18Watt warm white florescent long-life bulb (Philips, Holland) fixed above 1

m high from the trolleys providing a light intensity (PPFD) of 7mol m-2 s-1. In all

photoperiod chambers, the lamps were switched on automatically at 1600 h for a

duration dependents on the day length required. These chambers were continuously

ventilated with the help of micro exhaust fan (Fan-0051, SUPERMICRO USA)

with an average air speed of 0.2 m.s-1 over the plants when inside the chambers, to

minimize any temperature increase due to heat from the lamps. Temperature and

solar radiation were measured in the weather station situated one kilometer away

from the research venue. Temperature was recorded with the help of

Hygrothermograph (NovaLynx Corporation, USA) while solar radiation was

estimated using solarimeters (Casella Measurement, UK). Six plants were

reciprocally transferred from LD to SD and vice versa on every fourth day from

emergence until the appearance of first flower whereas 20 plants were kept as

controls in either chamber.

Plants were regularly watered by hand and a nutrient solution [(Premium Liquid

Plant Food and Fertilizer (NPK: 8-8-8); Nelson Products Inc. USA)] was applied

twice a week. Plants were observed daily until the end of experiment. Time to

flowering (corolla fully opened) from emergence was counted. The analytical

approach applied has been defined in Section 4.5.1.3 (Adams et al., 2003). Data

were analysed using the regression statistical technique of GenStat-8 (Lawes

Agricultural Trust, Rothamsted Experimental Station, U.K. and VSN International

Ltd. U.K.).

Table 4.5.1 Environmental detail of experiment 4.5 (June 15, 2006).

Growing Season Diurnal temperature (ºC) Daily light integral

08:00-16:00 Maximum Minimum Average June 2006 41.33 25.37 33.35 9.86 MJ.m-2.d-1 July 2006 40.65 27.74 34.19 9.23 MJ.m-2.d-1 August 2006 38.29 26.74 32.52 9.31 MJ.m-2.d-1 September 2006 37.60 24.00 30.80 9.69 MJ.m-2.d-1 October 2006 33.61 20.58 27.10 8.53 MJ.m-2.d-1

Table 4.5.2 Environmental detail of experiment 4.5 (June 15,

2007).

Growing Season Diurnal temperature (ºC) Daily light integral

08:00-16:00 Maximum Minimum Average June 2007 41.33 27.47 34.40 10.12 MJ.m-2.d-1 July 2007 38.32 26.13 32.23 9.76 MJ.m-2.d-1 August 2007 37.61 27.06 32.34 9.50 MJ.m-2.d-1 September 2007 36.53 23.10 29.82 9.69 MJ.m-2.d-1 October 2007 34.16 15.39 24.77 8.64 MJ.m-2.d-1

4.5.3 Results

4.5.3.1 Pansy cv. Baby Bingo (LDP)

Pansy cv. Baby Bingo flowered 58 days after emergence under continuous LD

whereas plants under continuous SD took 71 days to flower (Fig 4.5.3(A), Table

4.5.3). The durations of the development phases of photoperiod sensitivity are

shown in Table 4.5.4. The duration of juvenile phase of development (a1) was

recorded 16 days. However, the duration of other photoperiod-sensitive phases

were much less affected than the juvenile phase such as the duration of

photoperiod-sensitive phases in LD (PIL and Pd) was recorded only 5 days. The

duration of photoperiod-sensitive inductive phase in SD (PIS) was 18 days

photoperiod-insensitive flower development phase (a3) was the extended up to 38

days.

4.5.3.2 Snapdragon cv. Coronette (LDP)

Snapdragon cv. Coronette flowered 92 days after emergence under continuous LD

whereas plants under continuous SD took 127 days to flower (Fig 4.5.3(B), Table








days.

4.5.3.3 Petunia cv. Dreams (LDP)

Petunia cv. Dreams flowered 58 days after emergence under continuous LD

whereas plants under continuous SD took 81 days to flower (Fig 4.5.4(A), Table








days.

4.5.3.4 Cosmos cv. Sonata Pink (SDP)

Cosmos cv. Sonata Pink flowered 88 days after emergence under continuous LD

whereas plants under continuous SD took 60 days to flower (Fig 4.5.4(B), Table





photoperiod-sensitive phases in SD (PIS and Pd) was recorded only 10 days. The

duration of photoperiod-sensitive inductive phase in LD (PIL) was 37 days


days.

Same experiment was repeated in June 15, 2007 to confirm these results and 2-4


pattern as observed in the first year of experiment (June 15, 2006) i.e. a non-



was 0.88ºC and light integrals difference was 0.22 MJ.m-2.d-1.

Table 4.5.3 Effect of long days and short days on flowering time of Pansy cv. Baby Bingo, Snapdragon cv. Coronette, Petunia cv. Dreams and Cosmos cv. Sonata Pink. Standard errors of means are shown in parenthesis.

Name of LDPs Days to flower LD SD

Pansy cv. Baby Bingo 58.20 (±0.29) 71.20 (±0.49) Snapdragon cv. Coronette 92.00 (±0.54) 126.90 (±0.43) Petunia cv. Dreams 57.90 (±0.38) 80.60 (±0.31)

Name of SDP Cosmos cv. Sonata Pink 88.40 (±0.52) 60.20 (±0.29)

Table 4.5.4 The durations of the phases of photoperiod sensitivity of three LD annual ornamentals, Pansy cv. Baby Bingo, Snapdragon cv. Coronette, Petunia cv. Dreams and one SD annual ornamental Cosmos cv. Sonata Pink. Values in parenthesis are the standard errors of the estimates of the parameters of the model fitted using the FITNONLINEAR directive of GenStat-8. Name of LDPs a1 PIL Pd PIS a3 r2

Pansy cv. Baby Bingo 15.70 (0.79)

2.03 (4.29)

2.79 (3.21)

17.60 (1.45)

37.63 (0.92)

0.98

Snapdragon cv. Coronette 30.12 (0.82)

6.54 (0.67)

0.12 (0.94)

41.32 (1.11)

55.33 (0.39)

0.97

Petunia cv. Dreams 15.54 (0.67)

5.44 (0.56)

0.28 (0.73)

28.25 (0.93)

36.62 (0.38)

0.99

Name of SDP a1 PIS Pd PIL a3 r2

Cosmos cv. Sonata Pink 15.38 (0.70)

6.33 (0.48)

3.96 (0.76)

37.06 (0.96)

34.79 (0.34)

0.99

N.B. Student t-test was used to compare means.

4.5.4 Discussion

Previous experiments were based on assumption that all cultivars are equally

sensitive to photoperiod and light integral throughout development. This

assumption is tested in present experiment using Pansy, Snapdragon, Petunia

(LDPs) and Cosmos (SDP) for their photoperiod sensitivity. It was revealed that

these annuals showed a distinct response towards their inductive environment and

five flower development phases were estimated when a non-linear model was

applied. However, the duration of these flower development phases varies in

different annual species. Plants grown under inductive environment flowered after

58 days (Pansy cv. Baby Bingo and Petunia cv. Dreams), 92 days (Snapdragon cv.

Coronette) and 60 days (Cosmos cv. Sonata Pink) i.e. 13 (Pansy), 23 (Petunia), 35

(Snapdragon) and 28 days (Cosmos) earlier flowering than those grown in non-

inductive environment.

Findings of some previous studies on Pansy are in line with the results of present

experiment i.e. plants grown in LD flowered earlier. For example, Pansy cv.

Crystal Bow flowered after 74 days from sowing when grown under 16 h.d-1 LD

environment at 20 ºC (Karlsson, 1996). Similarly, Adams et al. (1997a) reported

that rate of progress to flowering increased significantly under LD (17 h.d-1) in

Pansy cv. Universal Violet. It is also reported that Petunia cv. Express Blush Pink

flowered 30 days earlier when received 16 h.d-1 LD at an average temperature of

28.7 ºC as compared to 8 h.d-1 SD environment. In present study the difference in

flowering time of Petunia cv. Dreams was 23 days. This difference could be due to

the increase in photoperiod (17 h.d-1) and temperature (31.6 ºC) and cultivar

variability. In another study Petunia cv. Midnight Madness required 8 to 10 more

days for flowering in SD (8 h.d-1) compared to plants grown in 16 h.d-1 (Karlsson,

1996). Munir (2003) obtained 23 days earlier flowering when Snapdragon cv.

Chimes was grown in LD (17 h.d-1) at 19.4 ºC. However, in present study this

difference was 35 days between LD and SD environment. The reason could be the

variation in cultivars and their genetic makeup as cv. Coronette is a mid-flowering

cultivar while cv. Chimes is an early-flowering one. High temperature (31.6 ºC)

could be another cause of this difference. Cosmos cv. Sonata Pink flowered earlier

in SD environment and Warner (2006) obtained a similar response also. However,

Kanellos and Pearson (2000) obtained an opposite response in Cosmos

atrosanguineus and reported that plants in LD (17 h.d-1) flowered 33 days earlier

than those at 8 h.d-1. The LD response of this plant could be due to the difference

in the species as Cosmos bipinnatus specie was tested in the present study. It is

also reported that LD environment delayed flowering in SDPs such as

Chrysanthemum cv. Snowdon (Adams et al., 1998a), Oryza sativa (Collinson ey

al., 1992) and Glycine max (Collinson ey al., 1993).

Previous analyses of the phases of photoperiod sensitivity (Collinson et al., 1992,

1993; Ellis et al., 1992, 1997; Yin et al., 1997; Adams et al., 1998a,b, 1999, 2003;

Bertero et al., 1999) have successfully analysed all of the flowering data

simultaneously to quantify the duration of flower development phases using

reciprocal transfer technique. Flowering time data were effectively estimated using

the same technique in Pansy, Snapdragon, Petunia and Cosmos. Results of present

research revealed that the duration of photoperiod-sensitive juvenile phase (a1) was

shorter than the photoperiod-sensitive phase in inductive environment (PIS in LDPs

Pansy, Snapdragon and Petunia and PIL in SDP Cosmos) and photoperiod-

insensitive flower development phase (a3). Although photoperiod increased the

duration of juvenile phase in Petunia cv. Express Blush Pink but light integrals

caused a dramatic increase in the length of this phase of development (Adams et

al., 1999). However, in Snapdragon cvs. Chimes, Liberty, Annabel, Bells, La

Bella, Pirouette, Ribbon and Sonnet the duration of juvenile phase was short as

compared to PIS and a3 phases and varied within the cultivars (Adams et al., 2003).

In another study on Snapdragon cv. Chimes Munir (2003) reported that the

duration of these phases are not only affected by photoperiod but light integrals

and temperature also had a significant effects i.e. low light integrals and low

temperature enhanced the duration of a1, PIS and a3. Munir (2003) also compared

CENTRORADIALIS (CEN) mutant of Snapdragon with wild type using reciprocal

transfer tool and reported that CEN gene present in wild type reduced the duration

of juvenile phase up to 10 days. CEN gene is expressed in the inflorescence apex a

few days after floral induction (after perceiving the LD inductive signal),

interacting with the floral meristem identity gene FLORICAULA (FLO) to regulate

flower position and morphology at the spike and carries on its determinate

inflorescence growth. However, mutant CEN first terminates the inflorescence

growth (indeterminate inflorescence) and then FLO genes produce flowers. The

size of CEN mutant is obviously shorter than the Wild type one. Its counterpart,

TERMINAL FLOWER 1 (TFL1) plays a similar role in Arabidopsis. But, unlike

CEN, TFL1 is expressed during the vegetative phase and therefore affects all

phases (vegetative and reproductive) of development (Bradley et al., 1997;

Ratcliffe et al., 1998, 1999).

In Pansy (LDP) and Cosmos (SDP) no such type of research has been reported

previously. However, the photoperiod sensitivity response of Pansy was similar to

Snapdragon and Petunia and the reason for shorter duration of a1 could be the same

as described above. Cultivars of these LDPs were most sensitive under non-

inductive SD environment (PIS phase). However, this duration was shorter than the

flower development photoperiod-insensitive phase (a3) in all three LDPs. The

reason could be that during PIS phase plants remain vegetative (produce leaves) in

non-inductive environment (SD) while in a3 phase of flower development plants

use the reserved assimilates because floral parts are incapable to do photosynthesis

hence the duration of this phase is longer than PIS phase (Munir 2003).

In Cosmos the duration of photoperiod-sensitive juvenile phase (a1) was shorter

(15 days) than the photoperiod-sensitive phase in LD inductive environment (PIL)

and photoperiod-insensitive flower development phase (a3). In contrary to LDPs,

the duration of PIL was two days longer in LD environment (37 days) as compared

to a3 phase (35 days) however this difference seems to be non-significant

statistically. Similarly, Collinson et al. (1993) reported that the duration of the

photoperiod-insensitive phase (juvenile phase) varied three-fold between cultivars

of Glycine max, i.e. from 11 to 33 days and the duration of the photoperiod-

sensitive phase (PIL) was greater in LD (non-inductive environment). However,

there was little variation in the photoperiod-insensitive post-inductive phase (a3), it

ranged from 15 to 20 days. Working on Chrysanthemum cv. Snowdon (SDP)

Adams et al. (1998a) observed that plants were capable of responding to SD

immediately after pinching. When they had received a sufficient number of SD (5

SD) they became induced to flower, although the leaf number of plants could be

increased by the subsequent use of LD, suggesting LD could still delay

inflorescence initiation. Plants needed a further 2–3 SD before the meristem was

committed to flower.

In this study, reciprocal transfer experiment has been shown to be a useful tool in

understanding how photoperiod environment influences the flowering process.

Although the effects of photoperiod and light integral on time to flowering have

been investigated in previous studies, the data presented here have shown which

developmental phases are most sensitive particularly in Pansy and Cosmos as no

attempt has been made previously to quantify their flower developmental phases.

General flowering models tend to ignore the phases of sensitivity to photo-thermal

environment. The model applied here provides the basis of a more physiologically-

based quantitative model of flowering. Many flowering studies have concentrated

on flower induction, the biochemical changes that occur within the plant at this

time, and the associated genetics. Consequently, juvenility and the later phases of

flower development tend to be ignored, despite their importance in the overall

flowering process. Therefore, the commercial benefits from the use of day

extension at a particular time could be significant.

56

58

60

62

64

66

68

70

72

74

0 10 20 30 40 50 60

Days of transfer from emergence

Day

s to

flo

wer

ing


A

85

90

95

100

105

110

115

120

125

130

0 10 20 30 40 50 60 70 80 90


Day

s to

flo

wer

ing


B

Fig 4.5.3(A,B) Effect of transferring plants from LD (17h.d-1) to SD (8h.d-1) (○)

and from SD to LD () at regular intervals from seedling emergence, starting on

15th June 2006 of (A) Pansy cv. Baby Bingo and (B) Snapdragon cv. Coronette.

The vertical bars (where larger than the points) represent the standard error within

replicates. The solid lines show the fitted relationships (Table 4.5.4 for parameters

estimates) for plants transferred from LD to SD and from SD to LD respectively.

56

60

64

68

72

76

80

84

0 10 20 30 40 50 60


Day

s to

flo

wer

ing

Petunia cv. Dreams

A

55

60

65

70

75

80

85

90

0 10 20 30 40 50 60


Day

s to

flo

wer

ing


B

Fig 4.5.4(A,B) Effect of transferring plants from LD (17h.d-1) to SD (8h.d-1) (○)

and from SD to LD () at regular intervals from seedling emergence, starting on

15th June 2006 of (A) Petunia cv. Dreams and (B) Cosmos cv. Sonata Pink. The

vertical bars (where larger than the points) represent the standard error within

replicates. The solid lines show the fitted relationships (Table 4.5.4 for parameters

estimates) for plants transferred from LD to SD and from SD to LD respectively.

CHAPTER 5

SUMMERY

Five experiments were designed to investigate the flowering response of important

summer (long day) and winter (short day) ornamental annuals to different light

environment. However, a sixth experiment was designed to study plant height

variable in ornamental annuals usually grown for cut flower production, keeping

the consumer’s preference in view.

The findings of first experiment illustrated an enhanced flowering response in all

plants when grown under their respective inductive environment such as short day

plants (Zinnia cv. Lilliput, Sunflower cv. Elf, French Marigold cv. Orange Gate,

African Marigold cv. Crush, Cockscomb cv. Bombay and Cosmos cv. Sonata Pink)

took minimum time to flower when exposed to short day length (shorter days and

longer nights). Hence, these plants received low light integrals (PAR), which

enabled them to recognize the floral signal and induce flowering. When the seeds

of these plants were sown late in January, plants received long days and high light

integrals, which eventually increased their flowering time. A most likely response

was observed in long day plants (Moss Rose cv. Sundance, Pansy cv. Baby Bingo,

Snapdragon cv. Coronette, Petunia cv. Dreams, Pot Marigold cv. Resina, Annual

Phlox cv. Astoria Magenta, Cornflower cv. Florence Blue, Oriental Poppy cv.

Burning Heart, Flax cv. Scarlet Flax and Annual Verbena cv. Obsession). These

plants were raised in full sunshine long day environment (longer days and short

nights) took minimum time to flower. They also received high light integrals at

flowering time therefore easily recognized the floral stimulus and produced

inflorescence or flower. Flowering time was delayed in LDPs when sown late

(July) because at flowering time they received short days and low light integrals,

which subsequently affect flower induction process. The findings of first

experiment provided important first hand information about the general flowering

behaviour of those cultivars, which were further examined in forthcoming

controlled photoperiod experiments.

Second experiment was designed to study flowering response under four distinct

controlled day length / photoperiods (8, 11, 14 and 17 h.d-1 for facultative LDPs

and SDPs; 11, 13, 15 and 17 h.d-1 for obligate LDPs). A curvilinear response was

observed in almost all cultivars. Facultative LDPs (Moss Rose cv. Sundance,

Pansy cv. Baby Bingo, Snapdragon cv. Coronette, Petunia cv. Dreams and Annual

Verbena cv. Obsession) grown under 14 and 17 h.d-1 photoperiods took minimum

time to flower however it was significantly increased when photoperiod decreased

i.e. 11 and 8 h.d-1. Similar trend was observed in obligate LDPS (Pot Marigold cv.

Resina, Annual Phlox cv. Astoria Magenta, Cornflower cv. Florence Blue, Oriental

Poppy cv. Burning Heart and Flax cv. Scarlet Flax) i.e. time to flowering was

minimum when these plants were grown under 15 and 17 h.d-1 photoperiods.

Flowering time was significantly increased when photoperiod decreased i.e. 13 and

11 h.d-1. An opposite flowering response but similar trend was observed in short

day plants (Zinnia cv. Lilliput, Sunflower cv. Elf, French Marigold cv. Orange

Gate, African Marigold cv. Crush, Cockscomb cv. Bombay and Cosmos cv. Sonata

Pink) i.e. SDPs when grown under 8 h.d-1 photoperiod took minimum time to

flower however it was decreased when photoperiod increased i.e. 11, 14 and 17

h.d-1. Some SD cultivars showed a non-significant difference when grown in 8 or

11 h.d-1. Cultivars of LDPs and SDPs took slightly more days (a week or so) as

compared to first experiment. This indicated that flowering process might be

affected because of light intensity or light integrals. Rate of progress to flowering

(per day) was also estimated for each cultivar, which showed a rapid progress

under inductive environment i.e. 17 h.d-1 for LDPs and 8 h.d-1 for SDPs. It was

decreased significantly with alteration in photoperiod in either case. Moreover,

data pertaining to rate of progress to flowering were also validated by fitting them

against the predicted ones, which indicated an acceptable fit as most of values were

plotted near the line of identity.

Third and fourth experiments were conducted to investigate flowering response of

important ornamental annuals under different artificial (light intensities) and

natural light integrals (shade levels). In third experiment LDPs (Moss Rose cv.

Sundance, Pansy cv. Baby Bingo, Snapdragon cv. Coronette, Petunia cv. Dreams,

Annual Verbena cv. Obsession, Pot Marigold cv. Resina, Annual Phlox cv. Astoria

Magenta, Cornflower cv. Florence Blue, Oriental Poppy cv. Burning Heart and

Flax cv. Scarlet Flax) and SDPs (Zinnia cv. Lilliput, Sunflower cv. Elf, French

Marigold cv. Orange Gate, African Marigold cv. Crush, Cockscomb cv. Bombay

and Cosmos cv. Sonata Pink) were grown under four light intensities (42, 45, 92

and 119 µmol.m-2.s-1). The results of this experiment revealed that LDPs grown

under high light intensity (119 µmol.m-2.s-1) flowered in minimum time whereas

SDPs grown under low light intensities (42 and 45 µmol.m-2.s-1) bloomed in

minimum duration. On the other hand, LDPs and SDPs were grown under 0%,

20%, 30% and 40% shade in fourth experiment. The findings of this experiment

coincided with the results obtained from third experiment (light intensity). LDPs

grown under low light integrals (40% shade) significantly delayed flowering as

compared to control and other treatments. Time to flowering decreased when shade

light integrals increased i.e. 30%, 20% and 0% shade levels. An opposite response

was observed in SDPs i.e. flowering time was delayed when plants were grown

under high light integrals (0% shade). SDPs when grown under low light integrals

(40% shade) took minimum time to flower. The results of both experiments

conducted under artificial and natural environment indicated that all these cultivars

were significantly affected by the light integrals.

In first four experiments, the general response of flowering to the day length /

photoperiod environment was quantified by using the general photoperiod model.

However, this model assumes that all cultivars are equally sensitive to photoperiod

throughout development. Therefore, this assumption was tested in the subsequent

experiment (five). Due to limited availability of space only four plants, three LDPs

(Pansy cv. Baby Bingo, Snapdragon cv. Coronette and Petunia cv. Dreams) and

one SDP (Cosmos cv. Sonata Pink) were selected to study their different phases of

photoperiod sensitivity. The duration of five developmental phases was estimated

in all four plants by transferring them from non-inductive to inductive

environments. Data of each cultivar were analysed using a non-linear model. The

response of the plants is described by five developmental phases, a photoperiod-

insensitive juvenile phase (a1), photoperiod-sensitive flower induction (PIL) and

flower development (Pd) phases in LD, a photoperiod-sensitive phase for flowering

in SD (PIS) and a photoperiod-insensitive flower development (a3) phase. The

duration of these phases varied in all four plants studied. Following germination,

Pansy, Snapdragon, Petunia and Cosmos passed through a distinct juvenile phase

(a1) during which they are not able to flower. After completion of juvenile phase

plants of all cultivars became receptive to recognize the signal. After this phase

when LDPs and SDP transferred to non-inductive environment they carried on to

develop flower and the non-inductive environment did not cease the floral

induction process (PIL and Pd phases). However, when plants were transferred

from non-inductive environment to inductive they took time to become competent

to recognize the signal. So this stage is labelled as photoperiod-sensitive phase

(PIS). After this phase plants entered into flower development phase (a3), which

seemed as photoperiod-insensitive phase.

After quantifying the flowering period and developmental phases in LDPs and

SDPs, last experiment was designed to control plant height which is second

preferable character after flowering particularly in cut flowers. Therefore, two

bedding plants viz. Moss Rose and Pansy were excluded in this experiment. Three

commonly used plant growth regulators (PGRs) viz. A-Rest (30 ppm.L-1), Bonzi

(30 ppm.L-1) and Cycocel (1000 ppm.L-1) were tested along with untreated checks

to control plant height in LDPs (Snapdragon cv. Coronette, Petunia cv. Dreams,

Annual Verbena cv. Obsession, Pot Marigold cv. Resina, Annual Phlox cv. Astoria

Magenta, Cornflower cv. Florence Blue, Oriental Poppy cv. Burning Heart and

Flax cv. Scarlet Flax) and SDPs (Zinnia cv. Lilliput, Sunflower cv. Elf, French

Marigold cv. Orange Gate, African Marigold cv. Crush, Cockscomb cv. Bombay

and Cosmos cv. Sonata Pink). Same plants’ cultivars were also grown under non-

inductive environment (LDPs under SD environment and SDPs under LD

environment) for 2, 4, 6 and 8 weeks duration. The results of this experiment

showed that use of PGRs reduce plant height significantly. More or less similar

results were obtained when plants were kept for short duration under non-inductive

environment.

CHAPTER 6

CONCLUSION

The first experiment was aimed to explore the possibility of plant

scheduling grown under ambient day length. Local gardeners and

nurserymen usually grow SDPs in LD and vice versa at the expense of

plant height. Present research findings expand the duration of growing

period for both LDPs and SDPs in their own responsive environment,

which can also be extended by raising them at later dates. By manipulating

the ambient day length time to display of bedding and cut-flower plants can

be prolonged in the garden, parks and indoor. Moreover, the duration of

availability of these plants in the market can also be enhanced.

The results of second experiment showed that flowering time can be

extended by controlling the photoperiod environment. LDPs grown under

SD environment took long time to flower. Therefore, non-inductive

environment (SD) lengthened the juvenile phase. Similarly, SDPs grown

under LD environment took more time to flower as non-inductive

environment (LD) stretched the duration of juvenile phase. By combining

the findings of experiments one and two plant scheduling technique for

year-round production can be efficiently used in ornamental annuals.

The outcome of third and fourth experiments can be incorporated for year-

round production of the ornamental annuals. LDPs grown under low light

intensity (42 and 45 µmol.m-2.s-1) or received low light integrals (40%

shade) maximized flowering induction time. On the other hand, flowering

time can also be extended if SDPs grown under high light intensity (92 and

119 µmol.m-2.s-1) or received high light integrals (0 and 20% shade). In

either case, a grower can also achieve his objectives by manipulating these

environmental factors to maintain the supply of ornamental annuals in the

market.

The findings of fifth experiment indicated that Pansy, Snapdragon, Petunia

and Cosmos have five distinct phases of photoperiod sensitivity. In both

LDPs and SDP, it was envisaged that these plants require 4-8 days of

inductive environment after completing juvenile phase. It means that the

supply of light (photoperiod) before and after this phase is mere wastage of

resources. However, transfer of plants from non-inductive environment to

inductive environment after completing the juvenile phase can be integrated

with the marketing demand. Hence, a continuous chain of supply of these

plants can be maintained in the market, which will ultimately increase the

income of the growers.

The results of last experiment indicated that plant growth regulators [A-

Rest (30 ppm.L-1), Bonzi (30 ppm.L-1) and Cycocel (1000 ppm.L-1)]

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