UNIVERSITI PUTRA MALAYSIA SOME PHYSIOLOGICAL STUDIES ON ORNAMENTAL IPOMORA BATATAS AS A GROUNDCOVER SPECIES NORIAH BT. OTHMAN FP 1991 6
UNIVERSITI PUTRA MALAYSIA
SOME PHYSIOLOGICAL STUDIES ON ORNAMENTAL IPOMORA BATATAS AS A GROUNDCOVER SPECIES
NORIAH BT. OTHMAN
FP 1991 6
SOME PHYSIOLOGICAL STUDIES ON ORNAMENTAL IPOMOEA BATATAS AS A GROUND COVER SPECIES
by
NORIAH BT . OTHMAN
Thesis Submitted in Fulfi lment of the Requirements for the Degree of Master of Agricultural Science in the Faculty of Agriculture,
Universiti Pertanian Malaysi a .
May 1991
ACKNOWLEDGEMENTS
I wish to express my s incere appreciation and thanks to my
supervisors, Professor Mohd . Zain Hj . Abdul Karim and Dr. Maheran Abd .
Aziz of Department of Agronomy and Horticulture, Universi t i Pertanian
Malaysia for their invaluable advice , guidance and encouragement
throughout the s tudy .
Special thanks to Encik Mohd . Said Saad , Lecturer , Department of
Agronomy and Horticulture, Universiti Pertanian Malaysia , for his kind
as s i s tance in providing some articles useful to the present s tudy . I
also wish to extend many thanks to Puan Sabariah Buang for her patience
in typ ing the manuscript, and to a l l the research and field staff at
V. P . M . who one way or other helped in the succes s of this project .
Las t , but not least , I wish to thank my husband, Abu Bakar, for
his help and encouragement, unders tanding and tolerance throughout the
duration of the s tudy .
i i i
TABLE OF CONTENTS
ACKNOWLEDGEMENTS ................................. . LIST OF TABLES ................................... .
LIST OF FIGURES .................................. .
LIST OF PLATES ................................... . ABSTRACT
ABSTRAK
CHAPTER
1 INTRODUCTION
2 LITERATURE REVIEW ......................... .
Int roduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Some Bot anical Aspects of Sweet Potato . . . . . .
Growth Pattern and Devel opment of Sweet Pot ato . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Maj or Factors Af fecting Growth of Sweet Pot ato . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Light . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Shade Tolerance . . . . . . . . . . . . . . . . . . . . . .
Chl orophyl l Content and Chl oropl ast Morpho l ogy in Sun and Shade P l ants . . .
Distribut ion o f Dry Matt e r in P lants . .
P l ant Nutrients
Ni t rogen . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Phosphorus . . . . . . . . . . . . . . . . . . . . . . . . . . .
iv
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v iii
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1
4
4
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5
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13
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15
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Potassium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Cal cium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Magnes i urn . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
3 MORPHOLOGICAL STUDIES OF TWO CULTIVARS OF SWEET POTATO................................ 21
Materia l s and Method . . . . . . . . . . .. . . . . . . . . . . . . . . . 21
P l ant ing Materia l s . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Experimental Design and Layout . . . . . . . . . . . . . 22
Observatio n and Data Col lection . . . . . . . . . . . . 23
Resul ts . . . . . . . . . . . . . . . . . . . . . . . • . . . . . . . . . . . . . . . 24
General Characteris t ics . . . . . . . . . . . . . . . . . . . . . 24
Leaf S hape and S ize . . . . . . . . . . . . . . . . . . . ...... 24
S tem Elongat ion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Growth of Thi rd Branch . . . . . . . . . . . . . . . . . . . . . . 32
Growth of Leaves on Main Stem . . . . . . . . . . . . . . 34
The Flowers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
The Storage Roots . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Discussion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
4 EFFECTS OF SHADING AND FERTILIZER LEVELS ON GROWTH OF THE 'VARIEGATED' CULTIVAR . . . . . • . . 41
Materials and Method . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Experimental Design and Layout . . . . . . . . . . . . 42
Management P ract ices . . . . . . . . . . . . . . . . . . . . . . 44
Data Col lection . . . . . . . . . . . . . . . . . . . . . ...... 46
v
Page
Resul ts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
Dry Wei ght . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . 48
Effect of Shadi ng . . . . . . . . . . . . . . . . . . . . . 48
Effect of Fert i l i zer Leve l s . . . . . . . . . . . 50
Growth of Mai n Stem . . . . . . . . . . . . . . . . . . . . . . . 52
Total Leaf Area . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
LAR and LALW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
Chl o rophyl l Content . . . . . . . . . . . . . . . . . . . . . . . 55
Qua l i ty Rat i ng of the P l ants . . . . . . . . . . . . . . 58
Nut r i e nt Content . . . . . . . . . . . . . . . . . . . . . . . . . . 59
Di scuss i o n . . . . . .. . .. . .. .. ... .. . . .. ... .. . . . .. 62
5 EFFECTS OF SHADE ON LIGHT COMPENSATI ON POINT . . . . . . . . . . . . . . . . . . . . . . . , ......... " . . . . 66
Mater i al s and Method . . . . . . . . . . . . . . . . . . . . . . . . 66
Resul ts . . . . . . . . , . . .. . . . . . . . . . . . . . .. . .... . . .. 70
Di scus s i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
6 MINERAL NUTRITION . . . . . . .. . . . . . . . . . . . . . . . .. . 7 7
Mater i a l s and Method . . . . . . . . . . . . . . . . . . . . . . . . 77
S i te of Experiment . . . . . . . . . . . . . . . . . . . . . . 79
Ster i l i z at i on of Equi pment . . . . . . . . . . . . . . 7 9
Nut r i ents i n Solution . . . . . . . . . . . . . . . . . . . . 7 9
Experimental Layout . . . .. . . . . . . . . . . . . .. . . 80
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Management of Nutrient Solution . . . . . . . . . . . . . 8 2
Control o f E l ec t r i cal Conduct iv i ty ( E . C ) . . 82
Cont rol of pH . . .. . . . . . . . . . . . . . . . . . . . . . . . . 8 2
Data Col lect i on . . . • . . . . . . . . . . • • . . . . . . . . . . . . . 8 3
Resul ts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
Growth o f t he P l ant Organs with Time . . . . • • • . 8 3
Nutrients Content of the P l ants . . . . . . . . . . . . . . 85
Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
7 GENERAL D I SCUSSION • . . . • • . . . . . • • • • • . . • • • . . . . . . . . . 92
8 SUMMARY . . . . . . . . . . . . . • . . • . . . . . . . . . . . . . . . . . . . . . . . . 9 5
BIBLIOGRAPHY 97
APPENDI CES
A - METEOROLOGI CAL DATA 105
B - DETERM I NAT ION OF CHLOROPHYLL CONTENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
C - DETERMINATION OF MINERAL NUTRI ENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
D - T - TEST . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
E - ANALYS I S OF VARIANCE . . . . . . . . . . . . . . . . . . . . . 120
F - GROWTH RATE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124
VITA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127
v ii
Table
1
2
3
4
5
6
7
8
9
10
11
12
1 3
LIST O F TABLES
Weekly I ncrements ( em ) of Main Stem of Two Sweet Potato Cul tivars Grown Under Lathhouse Condi tions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Weekly Increments ( em ) of Third Branch o f Two Sweet Potato Cultivars Grown Under Lathhouse Condi tions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Weekly Increments of Leaves of Two Sweet Potato Cul tivars Grown Under Lathhouse Condi tions . . . . . . . . . . . .
Light Intensi ties (mol m-2s-1 ) at Three Different Time at the Beginning of the Experiment ( A ) , and at Harves ting ( B ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Influence of Di fferent Leve ls of Ferti lizer on the Dry Wei ght of the Plants Grown Under Five Shade Leve l s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Growth of Main Stem ( em ) as Affected by S hades and Ferti l izer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The E ffects of Di fferent Shades and Ferti lizer L evels on LAR , LALW , Qual ity Ratings and Chlorophyll Content of the ' variegated' Cul tivar . . . . . . . . . . . . . . . . . .
Chlorophyl l Content. of Leaves ( mg/cm2 x 10-3) as Affected by Shades and Ferti l izer Level s . . . . . . . . . . . . . .
Influence of Di fferent Rates of Fert i l izer on Percentage of N, P , K , Ca and Mg Content Under Five Shade Levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Content of Elements ( % ) Based on Dry Wei ght of Leaves at Di fferent Shades and Fertilizer Level s . . . . . . Light Compensation Point ( umol m2s-1 ) of Two Sweet Potato Cul tivars Under Di fferent Shades Level . . . . . . . . . Light Saturation Point ( umol m2s-1 ) of Two Sweet Potato Grown Under Di fferent Level of Shades . . . . . . . . . . Content of E l ements ( % ) at the E nd of F ive Weeks Growth in Control led Nutrient Solution . . . . . . : . . . . . . . .
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Table Page
1 4 Amount of Nutrient s (%jg) Removed at F ive Weeks Growth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1 5 Amount of Nutrients ( %/g ) Removed b y cv. ' variegated ' P lanted in the Soil at the Age o f Twelve Weeks . . . . . . . 91
ix
LIST OF FIGURES
Figure
1 The Hypothetical Respons e of Photosynthesis t o Light I ntens ity and CO2 Concentration . . . . . . . . . . . . . . . .
2 Length of Main Stem of Two Sweet Potato Cult ivars Under Lathhouse Condit ions . . . . . . . . . . . . . . . . . . . . . . . . . . .
3 Length of Third Branch of Two Sweet Potato Cultivars Under Lathhouse Conditions . . . . . . . . . . . . . . . .
4 Number o f Leaves of the Main S t em Under Lathhouse
Page
7
30
33
Condi tions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
5
6
7
8
9
10
1 1
12
13
1 4
Diagram of the Factorial Experiment in Sp l it P l ot Des ign in Experiment 2 .............................. .
Diagram of the Shade House and the Posit ion of the Wooden Box . Each Shade House is Ful l y Cov ered with Sarlon Mesh of Dif f e rent Shade L ev el s . . . . . . . . . . . . . . . . I nf luence of Dif f erent Shade L evel s on t he Total Dry Weight of the P l ants Grown Under Four Fert il izer Leve l s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I nf l uence of Dif f e rent Levels o f Fertil iz er o n the Total Dry Weight of the P l ants Grown Under Five Shade Level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Growth of the Main S t em ( cm) as Aff ect ed by Shades and Ferti l iz e r Levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Total Leaf Area of 'variegated ' Cul t ivar Subjected to Diff erent Shading and Rates o f Fertil iz er Treatment at the End o f Three Month's Growt h . . . . . . . . .
Chl orophyl l Cont e nt of ' variegated ' L eave s Subj ect ed to Dif f e rent Shading and Rat e of Fertil iz er Treatments at the End of Three Month ' s Growth . . . . . . . .
Parkinson Leaf Chamber {ADC ) . . . . . . . . . . . . . . . . . . . . . . . . . Diagrammat ic S et-up of the Equipment . . . . . . . . . . . . . . . . .
Light Compensation Point of Two Sweet Potato Cul t ivars Under Dif f erent Shading Treatment s at the End of One Month's Growth . . . . . . . . . . . . . . . . . . . . . . . . . . . .
x
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45
49
51
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54
57
68
69
72
Figure
1 5
1 6
1 7
1 8
1 9
20
2 1
Regression o f Light Compensation Point on Shades in Two Cult ivars of Sweet Potato . . . . . . . . . . . . . . . . . . . . . . . . . Ligh t Saturation Curves for Both Cultivars Grown Under Different Levels of Shade . . . . . . . . . . . . . . . . . . . . . . . Hydroponic System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Diagram of Two Sweet Potato Cul tivars P lanted in Completely Randomized Block Design Under Hydroponic System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Dry Weight Accumulation of Two Sweet Potato Cultivars Grown in Contro lled Nutrient Solution
Nutrient Content of Leaves , Stem and Root s of Two Sweet Potato Cul tivars Grown in Controlled Nutrient Solution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Diagram of the Comp lete Module Used to Determine Nitrogen in Kj eldahl Digests by the Autoanalyser Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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7 3
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78
8 1
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III
LIST OF PLATES
Plate Page
1 The Two Sweet Potato Cultivars . . . . . . . . . . . . . . . . . . . . . . . . 25
2 The Branching Pattern of Both Cul tivars . . . . . . . . . . . . . . 26
3 Adaxial View of the ' variegated ' Leaves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 7
4 Abaxia l View of the ' variegated ' Leaves . . . . . . . . . . . . . 2 7
5 Adaxial View of the Leaves of cv . Imelda . . . . . . . . . . . . . . 29
6 Abaxial View of the Leaves of cv . Imelda ... . . . . . . . . . . . 29
7 The Flowers of cv . Imelda . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
8 Closer View of the Flower of cv . Imelda . . . . . . . . . . . , . . . 36
9 The S torage Roots of the Two Sweet Potato Cul tivars . . . 3 8
xii
Abs tract o f the thesi s presented to the Senate o f Universi t i Pertanian Mal aysia in fulfillment of the requirements for the degree of Master of Agricultural Science .
SOME PHYSIOLOGICAL STUDIES ON ORNAMENTAL IPOMOEA BATATAS AS A GROUND COVER SPECIES
by
Noriah Binti Othman
May 1 9 9 1
Supervisor Professor Mohd . Zain Haj i Abdul Karim
Facul ty Agricul ture
The morphological development and some physiological aspects were
s tudied on two cultivars of sweet potato whi ch are normally used as an
ornamenta l plant . Among the s tudies undertaken were those on the
botanical characteristics of the plants , effects of shade and
fertilizer and nutrient uptake . The cul tivar examined were Imelda and
an unnamed ' variegated ' type.
The effects of shading and fertilizer l eve l s showed growth of the
t variegated ' cul t i var were severely reduced in heavy shading (70% and
80%) . Increasing s hade level s i ncreased leaf area ratio ( LAR) and
leaf area to leaf weight ( LALW ) , but decreased dry matter production ,
visible quality , chlorophyll content and elemental composi tion in the
leaf tissue . However , ferti lizer levels were less effective than shade
in altering the parameters above. As shade l evel s increased , the
content of nitrogen , phosphorus , potas sium , calcium and magnesium in
xi i i
the l eaves increased . Shade levels signi fi cantly affected l i ght
compensation point (Lep) in both cul tivars . Increasing shade levels
decreased LCP . LCP of cv. ' variegated ' is lower than cv . Imelda ,
suggesting that cv . ' variegated ' i s more adaptable to a moderate shade .
S tudies on the nutrient uptake of both cul tivars using hydroponic
techniques showed that the highest element in the leaves , s tem and root
was potassium and fol lowed in descending order by nitrogen , calcium ,
phosphorus and magnesium . However , instead o f calcium , phosphorus was
higher in the root .
In general , both cultivars are suitable as groundcove r p l ants
with the 'variegated' cultivar more adaptab l e to shade than cv . Imelda .
xiv
Abstrak tesis yang dikemukakan kepada S enat Universiti Pertanian Malaysia sebagai memenuhi syarat untuk rj azah Master Sains Pertanian .
BBBBRAPA KAJIAN FISIOLOGI IB ATAS IPOMOEA BATATAS SRBAGAI SPESIBS TANAMAN HIASAN PRNUTUP BUMI
oleh
Noriah Binti Othman
Mei 1991
Penyel i a Profes'sor Mohd . Zain Haj i Abdul Karim
Fakulti Pertanian
P erkembangan morfologikal dan beberapa aspek fisiologikal telah
dikaj i ke atas dua kultivar ubi keledek yang biasanya digunakan s ebagai
tanaman hiasan . Kaj ian ini tertumpu pada ciri-ciri botanikal tanaman
ini , kesan baj a dan cahaya serta pengambi lan nutrien . Kultivar yang
dikaj i ialah Imelda dan j enis warna-warni yang tidak bernama.
Has i 1 kaj ian kesan teduhan dan baj a menunj ukkan pertumbuhan
kul t ivar yang berwarna-warni kel ihatan jelas terencat di bawah teduhan
yang tinggi ( 70% dan 80%) . Peningkatan paras teduhan telah menambahkan
kadar keluasan daun ( LAR ) dan kadar luas daU1\ p er berat daun (LALW),
tetap i mengurangkan penghasilan berat kering , kual i t i tanaman
dilihat dari sudut mata kasar , kandungan klorofil dan kompos i s i
elemen di dalam tisu daun . Namun demiki an , paras baja kurang memberi
kesan berbanding dengan teduhan di dalam mengubah parameter-parameter
di atas . Apabi l a paras baj a bertambah , kandungan nitrogen , posforus ,
xv
kalium , kalsium dan magnesium di dalam daun j uga turut bertambah . Paras
teduhan memberi kesan yang bererti pada tahap tepu cahaya ( LCP ) pada
kedua-dua kul tivar . Meninggikan paras teduhan menyebabkan tahap tepu
cahaya menurun . Kultivar berwarna-warni mempunyai LCP yang lebih rendah
dari kul tivar Imelda , mencadangkan kultivar berwarna-warni ini l ebih
dapat mengadaptasi pada keadaan teduhan yang s ederhana .
Kaj ian mengenai pengambilan nutrien pada kedua-dua kul tivar
menggunakan teknik hidroponik menunj ukkan elemen yang tertinggi di
dalam daun , batang dan akar ia lah kalium diikuti dalam susunan menurun
nitrogen , kals ium , posforus dan magnesium . Sungguhpun demikian ,
bukannya kal sium tetapi posforus lebih tinggi di dalam akar .
Amnya , kedua-dua kul tivar adalah sesuai sebagai tanaman penutup
bumi dan kul tivar yang berwarna-warni lebih dapat mengadaptas ikan diri
daripada kultivar Imelda .
CHAPTER 1
INTRODUCTION
The deve lopment o f the sweet potato ( Ipomoea batatas ) as a food
crop is as old as civi lization itsel f . Its ances tral home i s Tropical
America , in Central America or North Western South America ( Brand ,
1 9 7 1 ) . The species was an important food crop of the Mayans in Central
America and of the P eruvians in the Andes . Both civil izations
developed an advanced type of agriculture . Although maize was the
maj or crop , the natives also grew sweet potatoes . In fact by the time
of the discovery of America , they had extended the culture of thi s
important crop to Mexico , the Wes t Indies and certain parts of South
America ( Brand 1 9 7 1 ) .
Many records show that Spanish exp lorers of the early part of the
sixteenth century carried the plant , presumably by means of the fleshy
roots , in both the eas terly and wes terly directions , to Spain , Africa
and the Far Eas t ( Horne1 , 1 9 4 5 ) .
The pres ent day sweet potato w�s developed through centuries o f
culture in which a large number of cu1 tivars have risen through natural
hybridization and selection , mutations as well as through systematic
breeding efforts ( Purseglove , 1 9 6 8 ) .
One of the advantages of sweet potato compared to other tuber
crops , e . g . , tapioca , is that it is more drought tolerant ( Culwick ,
1
2
1 9 4 1 ) . Furthermore , the crop is considered useful as a famine reserve
( Brooke , 1 9 7 2 ) . Sweet potato has the advantage of being a good cover
crop , minimizing soil erosion and suppresses weed growth as wel l as
providing addi tional income from the tubers . The protective cover
provided by its vines reduces the e ros ivi ty of raindrops and run off ,
and competes we l l with weeds .
So far , s tudies on sweet potato have been emphas ized on the tuber
production and as food crop ( Lantican and Soriano , 1 9 6 1; B i swas and
Bos e , 1 9 80; Bartolini , 1 983) . Recentl y , two cul tivars of sweet potato
were introduced to Malays ia and were p l anted as ornamental groundcover
along the roadsides and under trees . One cul tivar is characterised by
large yel lowi sh green leaves believed to be originated from the
Phi lippines . The cultivar is known as Ime lda . It i s used as borders
of yield tests becaus e of i ts distinct colour at Phi l ippine Root Crop
Research & Training Center ( PRCRTC ) . However , i t is low yie lding and
is susceptible to attack by weevi l s ( Cylas formicarius ) . A second
cultivar is a ' variegated ' typ e with the l eaves having two different
co lours , i . e . dark green and purp li sh . It i s s aid to be originated
from Hawaii . Unfortunately the name of this cul tivar is s ti l l unknown .
The attractive colour of the leaves is the main reason that triggered
the interes t of some horti culturists to cul tivate them as ornamental
plants either as individual s or in combination with other ornamental
p lants to emphasiz e the colour and to give an appea ling look to
onlookers . Because there i s l ittle information on the two cul tivars ,
especi a l ly on the morphological and physiological behaviour under
3
Malaysian conditions, i t is essential that certain aspects of their
phys iology be studied . I t is hoped that these s tudies will help to
assess the potential of the cul tivars as ornamental groundcover .
Effects of varied light intensities on the growth of the p l ants ,
and mineral requirements for the growth and development o f the
cultivars are important phys iological aspects that wi l l contribute
towards our understanding of the physiological behaviour of the two
cultivars thus enabling us to provide the appropriate environment for
their growth . The s tudies reported here examine the aspects mentioned
above . With a better understanding o f the characterist i cs of these
two cultivars , i t is hoped that they can be grown as ornamentals under
appropriate conditions and es tabli sh as important groundcover plants in
Malaysia .
The specific objectives of the inves tigation reported in thi s
the s i s are:
1 . To s tudy the morpho logical development o f the two
cul tivars under lathhouse conditions ( Experiment 1 ) .
2 . To study the e ffects o f shading and different rates o f
fertil izer on the growth , nutrient composition and qua l i ty
of the 'vari egated ' cul tivar ( Experiment 2 ) .
3 . To determine the l i ght compensation point o f the two
cul tivars at varying degrees o f shading ( Experiment 3 ) .
4 . To s tudy the mineral requirement of the two cultivars
( Experiment 4 ) .
CHAPTER 2
LITERATURE REVIEW
Introduc t i on
Very l i t t l e s tud ies have been made on Ipomoea batat as f r om the
point of view of the use of the species f or ornament al purposes . The
review of l i terature therefore wi l l consi de r phys i ol ogical s tudies on
the spec i es as a whol e par t i cu l arly those aspects that re l at e to the
present i nves t igat i ons .
S ome Bot an i ca l Aspects of Sweet Potato
The sweet potato bel ongs t o the f ami ly Convolvul aceae , a group
whi ch c omprises about 50 genera, 1 20 0 or more species ( Pursegl ove ,
1 9 6 8 ) . The p l ant i s a twining perenn i a l herb but t reated as an annual
in cul t i vat i on . The p lants i n thi s fami l y have d i s t i ngui shing
characterist i cs : l atex i s present in the i r sap , the stems are erect,
t rai l i ng or cl imbing according t o the species , and contain b i c oll ateral
vascul ar bundles. Advent i t i ous roots are progress ive ly at the nodes
and i n thi s manner the p l ants creep a l ong ( Purseg l ove , 1 9 68) . The
f l owers are compl ete with a super i or p i st i l , f ive stamens , and a
trumpet shaped corol l a . The f ru i t i s a capsul e and the seed contains
an embryo with f olded cotyl edons ( Pursegl ove , 1 968 ) .
The major part of the t op system of the stem consi st s of primary
l ateral s . Varietal d i f f erences and simi l ar i t i es occured in l ength of
4
the main axis and
(Pursegl ove , 1 9 68).
5
in number of primary and secondary l aterals
The leaf system in the sweet potato deve lops a
re l at i vel y l arge number of simpl e , moderate l y l arge- bladed , l ong
pet iol ated leaf ( Purseg l ove , 1 9 68 ) . Hayward (1938) s t ated the first
l eaves were cordate whil e those formed l ater may be hastate , cut or
l obed. Thus the l eaf shade varies with the age of the pl ant.
The tubers are the f l eshy enl argement of cert ain of the l arger
roots and deve l op in the f irst 2 2 .5 cm of the soil . They are either
bunched together or borne on l ateral s , varying in length f rom several
cent imeter to 30 cm . The shape of the tubers cou l d vary considerabl y
even in the same variety depending on soil or other environmental
f actors (Pursegl ove , 1 9 6 8).
Growth Pattern and Development of Sweet Potato
Miltho rpe ( 1 967) and Mi l thorpe and Moorby ( 1 9 74 ) have described
the growth pattern of root crops ( with particul ar references to t he
pot at o , sugar beet and sweet potat o) as roughly consis t ing of three
vegetat ive phases . The phases comprise a pre-emergence or estab l ishment
phas e , a canopy deve l opment phase and the st orage or bul king phase .
Sweet pot at o may al so exhibit an initial l ag phase in which no
tubers are formed unt il a cert ain amount of l eaf growth has taken place
( Mil t horpe , 1 9 67). I n yet another pattern of growth there is
simu l t aneous shoot and tuber growth without the requirement f or an
6
ini t i al canopy development phase ( Lowe and Wi l son, 1 9 7 4 ) . There are
contras t i ng opinions as to the importance of l eaf area in the sweet
potat o . It has been shown that st aking the pl ants improves l eaf
d i s pl ay and increases Leaf Area Index ( LAI ) with the f i nal resu l t of
incre ased yields ( Chapman and Cowl ing , 1 9 6 5 ) . Haynes et al . , ( 1 9 6 7 )
beli eved in the exi s tence of an opt imal LAI . Lowe and Wil son (1 974 ) ,
on the other hand were of the opinion that the sink e f fect o f the
devel oping tubers was more cruci al in determi ning yield rather than
fol i age characteris t i cs . Nevertheless , t he i r work , showing that ear l y
v i go rous shoot growth delayed tube r bulking in gene ral and leading t o
lowered part i t i oning o f total dry matter to the tubers , seems to be
consi s tent with the concept of an opt imal LAI for economi c yi e l d .
Major Factors Affecting Growth of _Sweet Potato
Light
Growth of autotrophic pl ants is inf l uenced by the intenSity of
l i ght . Plants occupying sunny habi tats ( sun plants ) are general l y
capab l e of hi gher photosynthetic rates at high quantum f l ux densit i es
(l i ght intens i ty ) than pl ants restr i cted t oshaded locat ions ( shade
pl ant s ) ( Gabri e l sen , 1 9 6 0 ) .
At l ow quantum f l ux dens i t ies , photosyntheSis is l inearl y
dependent on quantum f l ux dens i ty and the e f f iciency of l ight as shown
in f i gure 1 ( Bjorkman , 1 9 8 1 ) . At higher quantum f lux densities, the
Respira tlOn PhotosynthesIs
-z -1 (umol CO2 m s )
/
/' / //
// / /
- - -/- - - - - - - - -- - - - - ---V
-------------
o ,1 .... /
LIght CompensatlOn
Pomt
Saturatmg LIght IntensIty
LIGHT INTENSITY
-2 -1 (UE m s )
HIgh CO 2
�ledlUm CO z
Low CO2
FIgure 1. The Hypothetical Response of PhotosynthesIS
to LIght IntensIty and C02 ConcentratlOn
"'-, 7
.....
8
increase in photosynthes i s i s less than proportional to the increase in
quantum flux dens ities ( partial light saturation ) and u ltimately ,
photosynthes i s fai l s to increase wi th increasing light intensi ty ( light
saturation ) ( Bj orkman , 1 9 8 1 ) .
Reduced light intens ity may a l s o s t imulate compensatory growth or
movement , including new chlorophyll producti on , epinasty and leaf
expansi on . In contras t , changes i n photop eriodism or in l ight-induced
germination are often controlled by very low light intensities and
brief exposure ( Bickford and Dunn , 1 9 7 2 ) .
The l i ght intensi ty at whi ch photosynthesis j us t balances
respiration ( net carbon dioxide exchange is zero ) is called the l ight
compensation point ( Salisbury and Ros s , 1 9 7 8 ) . This point varies wi th
the speci es , with the light intensi ty during growth ( Conover and Pool e ,
1 97 5 ) and to some extent wi th the temperature a t which measurements are
made and carbon dioxide concentrat i on ( Salisbury and Ross , 1 9 78 ) .
Species with a s teep photosynthet i c curve would be expected to show an
unfavourab le photosyntheti c balance when subjected to changed light o r
temperature whi l e those wi th sha l l ow curve would be expected t o b e
little a ffected by the environment ( Banni ster , 1 9 76 ) .
At atmospheric concentrations o f carbon di oxide , the values of the
light compensation point are s trongly influenced by temperature; this
effect may be very marked at high temperatures ann even at lower