Priming of field-sown rice seed enhances germination, seedling establishment, allometry and yield

Abstract Poor seedling establishment is a major

deterrent in adopting direct seeding of rice. Seed

priming to obtain better crop stand could be an

attractive approach. The objective of this study

was to determine the effectiveness of seed priming

strategies on the improved agronomic characters

of direct-sown rice. Seed priming strategies were:

hydropriming for 48 h, osmohardening with KCl

or CaCl2 for 24 h, ascorbate priming for 48 h and

seed hardening for 24 h, pre-germination (tradi-

tional soaking for nursery raising) and untreated

control. Seed priming improved germination and

emergence, allometry, kernel yield, and its quality,

whilst pre-germination displayed poor and erratic

emergence of seedling followed by poor plant

performance. Faster and uniform emergence was

due to improved a-amylase activity, which in-

creased the level of soluble sugars in the primed

kernels. Osmohardening with KCl gave greater

kernel and straw yield and harvest index, followed

by that of CaCl2, hardening and ascorbate prim-

ing. Improved yield was attributed principally to

number of fertile tillers and 1000 kernel weight. A

positive correlation between mean emergence

time and days to heading, while a negative one

between kernel yield and harvest index suggested

long-term effects of seed priming on plant growth

and development. The results suggest that physi-

ological changes produced by osmohardening

enhanced the starch hydrolysis and made more

sugars available for embryo growth, vigorous

seedling production and, later on, improved

allometric, kernel yield and quality attributes.

Keywords a-Amylase Æ Allometry Æ Direct

seeding Æ Osmohardening Æ Seedling vigor Æ Paddy

quality Æ Rice

Introduction

Traditionally, rice is transplanted after puddling,

while wheat cultivation followed by rice, requires

pulverized soil. This reflects an edaphic conflict in

traditional soil management for rice and its del-

eterious effects on the soil environment for the

succeeding wheat and other upland crops. Pud-

dling requires an excess of water at a time when

the reservoirs are low. Late onset of monsoon and

drudgery of operations often delay rice trans-

plantation, which leads to late vacation of fields,

forcing the sowing of wheat when the appropriate

time has passed. Furthermore, in view of the

M. Farooq Æ S. M. A. BarsaDepartment of Crop Physiology, University ofAgriculture, Faisalabad 38040, Pakistan

A. Wahid (&)Department of Botany, University of Agriculture,Faisalabad 38040, Pakistane-mail: [email protected]

Plant Growth Regul (2006) 49:285–294

DOI 10.1007/s10725-006-9138-y

123

ORIGINAL PAPER

Priming of field-sown rice seed enhances germination,seedling establishment, allometry and yield

Muhammad Farooq Æ Shahzad M. A. Barsa ÆAbdul Wahid

Received: 23 February 2006 / Accepted: 12 April 2006 / Published online: 3 November 2006� Springer Science+Business Media B.V. 2006

depleting water resources, it is desirable that rice

culture should also be like wheat so that it can

continually benefit the cropping system in

improving productivity. Direct seeding of rice,

may have certain benefits. Firstly, it eliminates

puddling and labor of nursery growing and

transplantation, and provides an option to resolve

the edaphic conflict. Secondly, it ensures the rice–

wheat cropping system and facilitates timely

establishment of succeeding winter crops. Lastly,

unlike puddled, direct-seeded fields show no soil

crack problems, saving irrigation water. In grow-

ing a successful direct-seeded crop, issues like

weed management and erratic emergence require

serious attention (Balasubramanian and Hill

2002). This necessitates finding strategies to

ensure faster and uniform crop stand.

Improved seed priming techniques are used to

reduce emergence time, accomplish uniform

emergence, better allometric (changes in growth of

plant parts over time) attributes and requisite stand

in many horticultural and field crops (Ashraf and

Foolad 2005; Farooq et al. 2005). These include

hydropriming, osmoconditioning, osmohardening,

hardening, and hormonal priming or soaking prior

to sowing (Basra et al. 2005; Ashraf and Foolad

2005). Effects of priming or pre-treatment of seed

persist under suboptimum field conditions, such as

salinity (Muhyaddin and Weibe 1989; Wahid et al.

2006), low or high temperature (Bradford et al.

1990; Pill and Finch-Savage 1988; Wahid and

Shabbir 2005) and low soil moisture availability

(Lee et al. 1998; Du and Tuong 2002). Different

seed priming tools have been successfully inte-

grated (Taylor et al. 1998; Basra et al. 2004; Farooq

et al. 2006b). Seed hardening is done in water (Lee

et al. 1998; Basra et al. 2005) and priming is per-

formed in a single cycle of wetting and drying (Lee

and Kim 1999). Until recently, Farooq et al.

(2006b) introduced a new technique of osmohar-

dening for rice seed invigoration, in which both

hardening and osmoconditioning were integrated.

Rice seeds were hardened in various salt solutions

instead of tap or distilled water. Osmohardening in

CaCl2 (ws –1.25 MPa) solution was more effective

for vigor enhancement than simple hardening.

Seed priming is beneficial in many respects.

For instance, it increases the activities of the

enzymes amylase and dehydrogenase in soybean

(Saha et al. 1990), and counteracts the adverse

effects on peroxidation of membrane lipids

(Bailly et al. 2000; Hsu et al. 2003). Seed priming

induces de novo biosynthesis of a-amylase (Lee

and Kim 2000), a key metabolic event in pro-

ducing vigorous seedlings. In a greenhouse study,

osmopriming (with CaCl2 and CaCl2 + NaCl)

improved seedling vigor and stand establishment

in flooded soil (Ruan et al. 2002). Likewise,

priming with 4% KCl solution or a saturated

CaHPO4 solution, increased plant density, fertile

tillers, and grain yield compared with unprimed

treatment when sown in soil with low moisture

content. This suggests that in drought-prone

areas, seed priming can economize seed rate, but

priming could be detrimental if seeding is done

when soil is at or near saturation (Du and Tuong

2002).

Although reports are available on the physio-

logical enhancements of direct-seeded rice (Du

and Tuong 2002; Ruan et al. 2002), no compre-

hensive study has evaluated the response of wide-

ranging seed priming treatments for enhancing

seedling establishment, plant allometry or the

quality of harvested paddy. Information is also

scarce on the physiological implications of prim-

ing-triggered enhancement in germination,

growth or yield, and their inter-relationships

using primed direct-seeded rice. It is surmised

that the priming of seed is beneficial in improving

the agronomic characters of rice under aerobic

conditions without compromising the quality of

harvested paddy. Here we tested this prediction

by evaluating the effects of a range of seed

priming strategies on germination, growth,

allometry and quality of harvested paddy as well

as some physiological determinants of growth

promotion in direct field-sown rice.

Material and methods

Experimental details and seed priming

treatments

Coarse rice (Oryza sativa L. cv. KS-282) seed for

this study was obtained from the Rice Research

286 Plant Growth Regul (2006) 49:285–294

123

Institute, Kala Shah Kakoo, Pakistan. Moisture

content of the seed was ca 8%. The study was

conducted in plots (6.5 m · 4.5 m) at a farm in

the rice growing belt during in the years 2004 and

2005. The experiment was laid out as a random-

ized complete block design (RCBD) with three

replications.

Seed priming treatments, chosen from the pre-

vious experience (Basra et al. 2005; Farooq et al.

2005, 2006a, b), were: (a) hydropriming, soaking

seed in aerated distilled water for 48 h, (b) hard-

ening, soaking seeds in tap water at 27�C ± 3 for

24 h and redrying to initial moisture content and

this cycle repeated once (Lee et al. 1998; Basra

et al. 2005; Farooq et al. 2005); (c, d) osmohar-

dening, similar to hardening but in the presence of

CaCl2 or KCl solutions of ws = –1.25 MPa

(Farooq et al. 2006b) and (e) ascorbate priming,

soaking seeds in an aerated solution of 10 mg l–1

ascorbic acid for 48 h. Pre-germination, soaking

seeds in water for 24 h followed by placing them

between two layers of saturated gunny bags up to

radicle appearance (chitting stage), was used to

compare the traditional rice sowing strategy for

raising nursery, while controls were seeds receiv-

ing no prior treatment. Primed seeds were given

three washings with water and re-dried closer to

original moisture (ca. 8%) under forced air at

27�C ± 3 (except for pre-emergence). These seeds

were put in polythene bags and stored in a

refrigerator at 5 ± 1�C until used.

Seed sowing and agronomic practices

Field soil was sandy clay loam with pH 8.1, elec-

trical conductivity 0.30 dS m–1 and organic matter

0.75%. Land was ploughed five times with tractor

drawn implements to achieve the required seed-

bed. Fertilizer was applied as urea (46%), single

superphosphate (18% P2O5), sulphate of potash

(50% K2O) and ZnSO4 (35% Zn) at recom-

mended doses. Whole quantities of phosphorus,

potash and zinc, and a half-dose of nitrogen were

applied prior to sowing. Remaining nitrogen was

applied in two equal splits, one at tillering and the

other at panicle initiation. Seed was hand drilled

at 65 kg ha–1 in 22 cm spaced rows on June 1,

2004. Plots were irrigated when the soil moisture

was slightly below field capacity. For weed

control, a mixture of ethoxy sulphuran and

phenoxyprop-p-ethyl at 200 g and 370 ml ha–1,

respectively was applied 20 days after sowing in

saturated soil. Ten irrigations were applied during

the crop growth period. Irrigation was halted

10 days prior to harvesting.

Emergence, growth and yield data

Days to start of emergence were recorded and

mean emergence time (MET), days to 50%

emergence (E50) and final emergence percentage

(FEP) were computed (Ellis and Roberts 1981).

Days taken from emergence to heading and from

heading to maturity were noted. Early at physi-

ological maturity (25 Aug), data on agronomic

characters were recorded four times at 15-day

intervals while spike and kernel characteristics

and yield components were recorded at full

maturity (25 Oct). Leaf area was measured using

a leaf area meter (Licor, Model 3100). Leaf area

index (LAI), crop growth rate (CGR), and net

assimilation rate (NAR) were calculated using

the formulae of Hunt (1978). The crop was har-

vested when fully ripe to determine paddy and

straw yield, and harvest index.

a-Amylase activity and soluble sugar content

For a-amylase activity, 1 g ground seed sample

was mixed with 10 ml phosphate buffer (pH 7.0)

and left for 24 h at 4�C. The enzyme activity was

determined from the supernatant by the DNS

method (Bernfeld 1955). For soluble sugars, 1 g

ground seed sample was mixed with 10 ml dis-

tilled water and left for 24 h at 25�C (Lee and

Kim 2000). The mixture was filtered (with

Whatman No. 42) and the final volume made to

10 ml with distilled water. Total soluble sugars

were determined by the phenol sulfuric method

(Dubois et al. 1956).

Spikelet and kernel quality characteristics

A common electric lamp with an adjustable stand

was used as a light source to determine the pan-

icle and kernel characteristics. A panicle was

positioned in front of the lamp so as to pass light

through it. This enabled the separation of sterile

Plant Growth Regul (2006) 49:285–294 287

123

spikelets or abortive (kernels that do not develop

after fertilization and look dull under light) and

opaque kernels within a spikelet. The chalky

kernels were separated by visually observing

chalky areas on them with a magnifying glass.

Length and width were taken of 100 kernels in

replicate with a digital caliper to determine

length:width ratio. Crude proteins from fresh

kernels were determined from total nitrogen

estimated by the microKjeldahl method (multi-

plied by the factor 5.95). Amylose content of the

fresh milled kernel and kernel water absorption

ratio was determined as described by Juliano

et al. (1965) and Juliano (1971).

Statistical analysis

Data were statistically analyzed using the software

MSTAT-C. Analysis of variance was used to test

the significance of variance sources, while LSD test

(p = 0.05) was used to compare the differences

among treatment means. Trend lines were set and

linear correlation coefficients were determined to

find the relationship of different attributes.

Results

Characteristics of primed seeds

Priming treatments increased the a-amylase

activity of kernels, which was in the order: KCl-

osmohardening > pre-germination > CaCl2-osmo-

hardening > hardening > ascorbate priming > hy-

dropriming > control (Fig. 1a). Maximum soluble

sugars were determined in KCl-osmohardened

kernels, followed by those of pre-germinated,

CaCl2-osmohardened, and hardened (Fig. 1b). A

strong positive correlation existed between in-

creased a-amylase activity and soluble sugars

content (Fig. 2).

Germination and seedling establishment

Seed priming treatments significantly changed

seedling emergence and establishment. Minimum

days to start of seedling emergence, MET, E50,

and greater FEP were obtained in seeds osmo-

hardened with KCl followed by CaCl2, hardened,

and ascorbate primed, whilst the reverse trend for

these attributes was evident in pre-germinated

and controls (Table 1).

Agronomic characters and yield components

All treatments, with significant differences,

reduced the time taken (in days) from emergence

to heading and from heading to maturity, except

control and pre-germination. This time was shorter

α-A

myl

ase

activ

ity (

units

)*

(a) b

f

a

ce d

0

2

4

6

8

10

12

Solu

ble

suga

rs (

mg

g-1 f

resh

wei

ght)

(b)

e

b

d

a

b

c

b

0

4

8

12

16

20

Seed priming treatments

Fig. 1 Effect of seed treatments on (a) a-amylase activityand (b) total soluble sugars in direct-seeded coarse rice.*One unit of the enzyme’s activity is the amount ofenzyme which released 1 lmol of maltose by 1 ml originalenzyme solution in 1 min. , control; , pre-germinated;

, hydropriming; , osmohardening (KCl); , osmohar-dening (CaCl2); , ascorbate priming; , hardening

288 Plant Growth Regul (2006) 49:285–294

123

in plants from KCl- and CaCl2-osmohardening

treatments followed by hardening and ascorbate

priming (Table 2). A positive correlation was no-

ted between MET and days to heading (Fig. 3a).

Priming treatments produced significant differ-

ences in most of the growth and yield attributes.

Plants originating from control and pre-germina-

tion treatments had remarkably short while those

from CaCl2- and KCl-osmohardening had long

statures compared to others. Reduced number of

total or fertile (panicle-bearing) tillers was re-

corded in pre-germination and controls plants;

nonetheless, this number reached a maximum in

hydropriming and osmohardening with KCl and

CaCl2 (Table 3). Branches or kernel numbers per

panicle did not differ much among the treatments

(data not shown), but 1000 kernel weight was the

greatest in KCl osmohardening, followed by

hardening and ascorbate priming. Seed priming

produced an increase in kernel number per panicle

and 1000 kernel weight led to increased kernel

yield, which was the greatest under KCl- and

CaCl2-osmohardening. Although all priming

strategies were effective in enhancing growth, yield

and yield components, osmohardening with KCl

was the best (Table 3). Osmohardening with KCl

yielded 0.32 kg m–2 and 0.90 kg m–2 kernel and

straw, respectively and a harvest index (26.34%).

These results were followed by treatments of

osmohardening with CaCl2, hardening, and ascor-

bate priming (Table 4). Inverse but close associa-

tions were noted of MET with kernel yield

(Fig. 3b) and harvest index (Fig. 3c), reflecting the

specific effects of priming on these attributes.

Allometry

Regardless of seed priming treatments, values of

all derived growth attributes were greater at mid-

harvest, compared to others, displaying maximal

growth and dry matter production early at phys-

iological maturity. Priming treatments improved

LAI at all harvests, KCl-followed by CaCl2-

osmohardening, and ascorbate priming (Fig. 4).

Likewise, osmohardening with KCl and CaCl2maximally improved CGR at all harvests.

Maximum value of NAR was derived in KCl and

CaCl2 osmohardened plants at first harvest and

osmohardened with CaCl2, KCl, and hardened

treatments at the second harvest (Fig. 4).

Spike and kernel quality characteristics

Priming strategies remarkably reduced the number

of sterile spikelets, as well as abortive, opaque, and

Fig. 2 Relationship between a-amylase activity and totalsugars in direct-seeded coarse rice as affected by differentseed priming treatments. *One unit of the enzyme’sactivity is the amount of enzyme, which released 1 lmolof maltose by 1 ml original enzyme solution in 1 min

Table 1 Effect of seedpriming on the seedlingestablishment of direct-seeded coarse rice

Treatmentmeans ± standard error.Means sharing samealphabets differ non-significantly

Treatments Days to startof emergence

Mean emergencetime (days)

Days to 50%emergence

Final emergence(%)

Control 4 ± 0.3a 6.6 ± 0.2b 5.3 ± 0.8a 80 ± 2.1dPre-germination 4 ± 0.3a 7.0 ± 0.2a 5.6 ± 0.6a 80 ± 2.1dHydropriming 3 ± 0.3b 6.0 ± 0.2c 4.3 ± 0.9ab 85 ± 1.9bOsmohardening (KCl) 2 ± 0.3b 4.7 ± 0.2e 4.0 ± 0.9b 88 ± 2.0aOsmohardening (CaCl2) 3 ± 0.4b 5.2 ± 0.2d 4.3 ± 0.8b 88 ± 2.3aAscorbate priming 3 ± 0.4b 5.9 ± 0.3c 4.8 ± 0.7ab 82 ± 2.4cHardening 3 ± 0.3b 4.9 ± 0.3e 4.4 ± 0.8b 84 ± 2.5bc

Plant Growth Regul (2006) 49:285–294 289

123

chalky kernels. Osmohardening with KCl and

CaCl2 followed by ascorbate priming and harden-

ing produced lower numbers of spikelets and

kernels with the above-mentioned characters,

whilst this number was greater in the case of pre-

germination and control (Table 4). No remarkable

differences were evident in kernel length and

width, although kernel length was the greatest in

both osmohardening treatments (data not shown).

Priming treatments improved kernel quality char-

acteristics in terms of crude protein and amylose,

the highest content of the former and lowest of the

latter being found in kernels from osmohardening

followed by hardening treatments. These changes

increased the kernel water absorption ratio in a

similar order (Table 4), which was substantiated by

a positive trend of kernel water absorption ratio

with crude proteins (Fig. 5a), but a negative one

with kernel amylose content (Fig. 5b).

Discussion

This study revealed that seed priming strategies,

with significant differences, promoted plant

growth and agronomic characters throughout the

ontogeny of rice. The changes produced in

primed kernels were crucial in this regard.

Osmohardening with KCl and CaCl2 exhibited

the most pronounced effect in enhancing seedling

vigor, as was evident from changes in germination

and seedling emergence (Table 1). This is

plausible because a positive correlation exists

between seed vigor and field performance of rice

(Yamauchi and Winn 1996). Furthermore, seed

priming produces more vigorous, faster, and uni-

form seedlings and their establishment (Hampton

and Tekrony 1995; Ruan et al. 2002; Zheng et al.

2002). This study revealed a direct relationship

between increased a-amylase activity and levels

of soluble sugars in primed kernels (Figs. 1, 2),

which support the view that seed priming either

induces the de novo synthesis or increases the

Table 2 Effect of seed priming on days to heading andmaturity of direct-seeded coarse rice

Treatments Emergence toheading days

Heading tomaturity days

Control 92 ± 6a 34 ± 2aPre-germination 96 ± 5a 34 ± 2aHydropriming 85 ± 6b 29 ± 2bOsmohardening

(KCl)79 ± 6c 24 ± 2cd

Osmohardening(CaCl2)

81 ± 5bc 26 ± 2bcd

Ascorbate priming 85 ± 6bc 27 ± 2bHardening 81 ± 6bc 25 ± 2cd

Treatment means ± standard error. Means sharing samealphabets differ non-significantly

Fig. 3 Relationship between mean emergence time and(a) days to heading (b) kernel yield and (c) harvest indexin direct-seeded coarse rice as affected by different seedpriming treatments

290 Plant Growth Regul (2006) 49:285–294

123

activities of existing enzymes (Sung and Chang

1993; Lee and Kim 2000), thereby producing

germination metabolites in requisite amounts.

The benefit of these changes was not lost during

re-drying, as was evident from better germination

(Table 1). Poor performance of pre-germinated

kernels in delayed and erratic emergence of

seedlings and subsequently poor plant perfor-

mance are due to the crippled ability of these

kernels to utilize germination metabolites

optimally.

Field appraisal of seed priming strategies was

made in terms of growth, allometry, and kernel

yield and its quality characteristics. Improved

plant height as noted here (Table 1) might be due

to earlier, uniform, and vigorous seedlings giving

a stronger and more energetic start. Improved

kernel and straw yield and greater harvest index

with seed priming is possibly due to enhanced dry

matter partitioning to the developing grain (Ta-

ble 3) as a result of greater CGR, NAR, and LAI

manifested at various growth stages (Fig. 4). The

inverse relationship of MET with kernel yield and

harvest index (Fig. 3) suggests that earlier estab-

lishment of seedlings had persistent effect on

subsequent plant growth and allometry. Among

the priming treatments, osmohardening with KCl

and CaCl2 greatly improved plant height and

reduced the days from emergence to heading and

from heading to maturity (Table 2). This is due to

the enhanced ability of these treatments to pro-

duce long-lasting and persistent changes on the

growth attributes and the timely accomplishment

of phenological events. Another manifestation of

seed priming was the substantial increase in the

number of total and fertile tillers (Table 4),

stemming from the events taking place during

earlier stages of crop growth such as faster

Table 3 Effect of seed priming on agronomic and yield characters of direct-seeded coarse rice

Treatments Plant height(cm)

No. of tillers(m–2)

No. of fertiletillers (m–2)

1000 kernelweight (g)

Straw yield(kg m–2)

Kernel yield(kg m–2)

Harvest index(%)

Control 82 ± 0.5bc 623 ± 58b 584 ± 4.2d 16.3 ± 2b 0.81 ± 0.02c 0.27 ± 0.09d 24.0 ± 0.2fPre-germination 80 ± 4.3c 676 ± 55bcd 574 ± 5.2d 15.3 ± 2b 0.80 ± 0.01c 0.26 ± 0.09de 24.5 ± 0.2eHydropriming 85 ± 5.0ab 738 ± 63a 659 ± 16.2a 16.7 ± 2b 0.84 ± 0.02a 0.28 ± 0.08d 24.8 ± 0.2dOsmohardening (KCl) 85 ± 4.6ab 729 ± 58ab 658 ± 14.2a 19.0 ± 1a 0.90 ± 0.02b 0.32 ± 0.08a 26.3 ± 0.2aOsmohardening (CaCl2) 88 ± 4.3a 656 ± 57cd 628 ± 13.9b 16.3 ± 2b 0.89 ± 0.02b 0.31 ± 0.09b 25.8 ± 0.2bAscorbate priming 82 ± 4bc 706 ± 63abc 643 ± 12.6ab 16.7 ± 2b 0.89 ± 0.09b 0.30 ± 0.09c 25.3 ± 0.3cHardening 84 ± 4.6abc 713 ± 65abc 611 ± 17.2c 17 ± 2ab 0.90 ± 0.03b 0.30 ± 0.09c 25.3 ± 0.2c

Treatment means ± standard error. Means sharing same alphabets differ non-significantly

Table 4 Effect of seed treatments on the spikelet and kernel characteristics of direct-seeded coarse rice

Treatments Sterilespikelets(%)

Opaquekernels(%)

Abortivekernels(%)

Chalkykernels(%)

Normalkernels(%)

Kernelprotein(%)

Kernelamylose(%)

Kernel waterabsorptionratio

Control 7.1 ± 0.1b 18.7 ± 2.2a 2.4 ± 0.05a 27.0 ± 0.6a 51.9 ± 8.8b 6.6 ± 0.2d 31.3 ± 0.4a 3.3 ± 0.1cPre-germination 7.3 ± 0.1a 17.7 ± 2.2abc 2.4 ± 0.05a 26.0 ± 0.6b 54.7 ± 9.1ab 6.5 ± 0.3d 31.5 ± 0.4a 3.1 ± 0.1dHydropriming 6.9 ± 0.2c 18.0 ± 2.2ab 1.9 ± 0.05b 25.7 ± 0.6b 54.4 ± 9.7ab 6.9 ± 0.3c 31.3 ± 0.4a 3.3 ± 0.1cOsmohardening

(KCl)5.5 ± 0.2f 15.3 ± 2.3d 1.5 ± 0.05e 20.6 ± 0.6e 55.5 ± 9.5ab 7.4 ± 0.3a 28.1 ± 0.4c 3.7 ± 0.1a

Osmohardening(CaCl2)

6.1 ± 0.1e 16.3 ± 2.3bcd 1.6 ± 0.05d 21.3 ± 0.6d 60.7 ± 9.7ab 7.2 ± 0.2ab 28.4 ± 0.3c 3.6 ± 0.2ab

Ascorbatepriming

6.4 ± 0.1d 16.3 ± 2.3bcd 1.8 ± 0.05c 22.7 ± 0.7c 59.2 ± 9.6ab 7.0 ± 0.2bc 29.5 ± 0.4b 3.5 ± 0.1b

Hardening 6.1 ± 0.1e 15.7 ± 2.4cd 1.6 ± 0.05e 21.0 ± 0.6de 61.7 ± 8.8a 7.2 ± 0.3ab 28.2 ± 0.5c 3.6 ± 0.1ab

Treatment means ± standard error. Means sharing same alphabets differ non-significantly

Plant Growth Regul (2006) 49:285–294 291

123

production of more vigorous seedlings. Previous

studies showed that seed priming in rice seedlings

led to more uniform, vigorous, and faster emer-

gence of seedlings, bestowing wide-ranging phe-

nological and yield-related benefits (Harris et al.

2002). Nonetheless, further investigations are

imperative on plant growth changes taking place

in time and space.

Plant allometry is an effective approach to as-

sess time course changes in growth and dry matter

accumulation (Niklas 1994). Improved LAI,

CGR, and NAR from primed direct-sown rice

(Fig. 4), might be due to improved efficiency of

the plant in the production and partitioning of

photosynthates to the developing reproductive

parts (Ashraf and Foolad 2005). Reduced emer-

gence to heading and heading to maturity days

from primed seeds also seemed to improve LAI,

CGR, and NAR (Fig. 4). Seed priming enhances

vigor and improves later growth in both coarse

and fine rice as revealed from previous compari-

sons of more versus less vigorous seedlings

(Yamauchi and Winn 1996; Basra et al. 2004,

2005).

The improved nutrient, photoassimilates, and

moisture supply in plants arising from primed

seeds results in lower numbers of sterile spikelets

for direct-seeded rice primed with salts of potas-

sium (Thakuria and Choudhary 1995). Seed

priming with KCl and CaCl2 improved kernel

quality characteristics in osmoprimed direct-

seeded rice under normal (Paul and Choudhary

1991) or stressful conditions (Zheng et al. 2002).

It appears that greater partitioning and uniform

distribution of photoassimilates due to osmohar-

dening treatments resulted in a greater number of

normal kernels with improved crude proteins and

reduced amylose content and/or lower number of

opaque, abortive, and chalky kernels (Table 4).

Reduced amylose content within specified limits

(Panlasigui et al. 1991) and increased protein

content are important determinants of kernel

quality. The positive relationship of crude pro-

teins and the negative one of amylose with water

absorption ratio (Fig. 5a,b) are plausible justifi-

cations for better kernel quality.

In crux, these findings strongly suggest that

seed priming is a pragmatic strategy in direct-

seeded rice. The physiological changes occurring

in kernels as a result of priming were important.

Of these, increased a-amylase activity hydrolyzed

more starch and made more soluble sugars

available and helped to promote vigorous seed-

lings, better plant growth, allometry, yield attri-

butes, and kernel quality characteristics. The

greater efficiency of osmohardening with KCl and

CaCl2 is related to the osmotic advantage that

both K+ and Ca2+ have in improving cell water

status, and also that they act as cofactors in the

activities of numerous enzymes, most of which are

Fig. 4 Influence of seed priming treatments on the (a) leafarea index (LAI), (b) crop growth rate (CGR) and (c) netassimilation rate (NAR) in direct-seeded coarse rice. ,control; , pre-germination; , hydropriming; ,osmohardening (KCl); , osmohardening (CaCl2); ,ascorbate priming; , hardening

292 Plant Growth Regul (2006) 49:285–294

123

active when reserve mobilization and radical

protrusion are in progress. These results may

have implications for growing rice in water

scarce-areas of the world.

Acknowledgment Financial help from the Higher Edu-cation Commission, Government of Pakistan, is acknow-ledged.

References

Ashraf M, Foolad MR (2005) Pre-sowing seed treat-ment—a shotgun approach to improve germination,plant growth, and crop yield under saline andnon-saline conditions. Adv Agron 88:223–271

Balasubramanian V, Hill JE (2002) Direct seeding of ricein Asia: emerging issues and strategic research needsfor 21st century. In: Pandey S, Mortimer M, Wade L,Tuong TP, Lopes K, Hardy B (eds) Direct seeding:research strategies and opportunities. InternationalResearch Institute, Manila, Philippines, pp 15–39

Basra SMA, Farooq M, Tabassum R (2005) Physiologicaland biochemical aspects of seed vigor enhancementtreatments in fine rice (Oryza sativa L.). Seed SciTechnol 33:623–628

Basra SMA, Farooq M, Hafeez K, Ahmad N (2004)Osmohardening: a new technique for rice seed invig-oration. Inter Rice Res Notes 29:80–81

Bailly C, Benamar A, Corbineau F, Come D (2000) Anti-oxidant systems in sunflower (Helianthus annuus L.)seeds as affected by priming. Seed Sci Res 10:35–42

Bernfeld P (1955) Amylases a and b. Method Enzymol1:149

Bradford KJ, Steiner JJ, Trawatha SE (1990) Seed priminginfluence on germination and emergence of pepperseed lots. Crop Sci 30:718–721

Dubois M, Giles KA, Hamilton JK, Roberes PA, Smith F(1956) Colorometric method for determination ofsugars and related substances. Ann Chem 28:350–356

Du LV, Tuong TP (2002) Enhancing the performance ofdry-seeded rice: effects of seed priming, seedling rate,and time of seedling. In: Pandey S, Mortimer M,Wade L, Tuong TP, Lopes K, Hardy B (eds) Directseeding: research strategies and opportunities. Inter-national Research Institute, Manila, Philippines,pp 241–256

Ellis RA, Roberts EH (1981) The quantification of ageingand survival in orthodox seeds. Seed Sci Technol9:373–409

Farooq M, Basra SMA, Hafeez K, Ahmad N (2005)Thermal hardening: a new seed vigor enhancementtool in rice. Acta Bot Sin 47:187–193

Farooq M, Basra SMA, Cheema MA (2006a) Integrationof pre-sowing soaking, chilling and heating treatmentsfor vigor enhancement in rice (Oryza sativa L.). SeedSci Technol 34:521–528

Farooq M, Basra SMA, Hafeez K (2006b) Rice seedinvigoration by osmohardening. Seed Sci Technol34:181–186

Hampton JG, Tekrony DM (1995) Handbook of ISTAvigour test methods, 3rd edn. ISTA, Zurich, p 10

Harris D, Tripathi RS, Joshi A (2002) On-farm seedpriming to improve crop establishment and yield indry direct-seeded rice. In: Pandey S, Mortimer M,Wade L, Tuong TP, Lopes K, Hardy B (eds) Directseeding: research strategies and opportunities.International Research Institute, Manila, Philip-pines, pp 231–240

Hsu CC, Chen CL, Chen JJ, Sung JM (2003) Acceleratedaging-enhanced lipid peroxidation in bitter gourdseeds and effects of priming and hot water soakingtreatments. Sci Hort 98:201–212

Hunt R (1978) Plant growth analysis. Edward Arnald,London

Juliano BO (1971) A simplified assay for milled riceamylose. Cer Sci 16:334–340

Juliano BO, Onate LU, Mundo AM (1965) Relation ofstarch compaction, protein content and gelatinizationtemperature to cooking and eating quality of milledrice. Food Technol 19:1006–1011

Lee SS, Kim JH (1999) Morphological change, sugarcontent, and a-amylase activity of rice seeds undervarious priming conditions. Kor J Crop Sci 44:138–142

Lee SS, Kim JH (2000) Total sugars, a-amylase activity,and emergence after priming of normal and aged riceseeds. Kor J Crop Sci 45:108–111

Fig. 5 Relationship between (a) kernel proteins and(b) kernal amylose with kernel water absorption ratio indirect-seeded coarse rice as affected by different seedpriming treatments

Plant Growth Regul (2006) 49:285–294 293

123

Lee SS, Kim JH, Hong SB, Yun SH (1998) Effect ofhumidification and hardening treatment on seedemergence of rice. Kor J Crop Sci 43:157–160

Muhyaddin T, Weibe HJ (1989) Effect of seed treatmentswith polyethyleneglycol (PEG) on emergence ofvegetable seeds. Seed Sci Technol 17:49–56

Niklas KJ (1994) Plant allometry. The University ofChicago Press, Chicago, Illinois

Panlasigui LN, Thompson LU, Juliano BO, Perez CM,Yiu SH, Greenberg GR (1991) Rice varieties withsimilar amylose content differ in starch digestibilityand glycemic response in humans. Amer J Clinic Nutr54:871–877

Paul SR, Choudhary AK (1991) Effect of seed primingwith salts on growth and yield of wheat under rainfedconditions. Ann Agric Res 12:415–418

Pill WG, Finch-Savage WE (1988) Effects of combiningpriming and plant growth regulator treatments on thesynchronization of carrot seed emergence. Ann ApplBiol 113:383–389

Ruan S, Xue Q, Tylkowska K (2002) Effects of seedpriming on emergence and health of rice (Oryzasativa L.) seeds. Seed Sci Technol 30:451–458

Saha R, Mandal AK, Basu RN (1990) Physiology of seedinvigoration treatments in soybean (Glycine max L.).Seed Sci Technol 18:269–276

Sung FJ, Chang YH (1993) Biochemical activities associ-ated with priming of sweet corn seeds to improvevigor. Seed Sci Technol 21:97–105

Taylor AG, Allen PS, Bennett MA, Bradford JK, BurrisJS, Misra MK (1998) Seed enhancements. Seed SciRes 8:245–256

Thakuria RK, Choudhary JK (1995) Effect of seed prim-ing, potassium and anti-transpirant on dry-seededrainfed ahu rice (Oryza sativa). Ind J Agron 40:412–414

Wahid A, Shabbir A (2005) Induction of heat stresstolerance in barley seedlings by pre-sowing seedtreatment with glycinebetaine. Plant Growth Regul46:133–141

Wahid A, Parveen M, Gelani S, Basra SMA (2006) Pre-treatment of seeds with H2O2 improves salt toleranceof wheat seedling by alleviation of oxidative damageand expression of stress proteins. J Plant Physiol(published online)

Yamauchi M, Winn T (1996) Rice seed vigor and seedlingestablishment in anaerobic soil. Crop Sci 36:680–686

Zheng HC, Jin HU, Zhi Z, Ruan SL, Song WJ (2002)Effect of seed priming with mixed-salt solution onemergence and physiological characteristics of seed-ling in rice (Oryza sativa L.) under stress conditions.J Zhejiang Uni 28:175–178

294 Plant Growth Regul (2006) 49:285–294

123