Plant Growth Regul (2006) 49:285–294 DOI 10.1007/s10725-006-9138-y

ORIGINAL PAPER

Priming of field-sown rice seed enhances germination, seedling establishment, allometry and yield Muhammad Farooq Æ Shahzad M. A. Barsa Æ Abdul Wahid

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

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 (traditional 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 increased 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 priming. Improved yield was attributed principally to

M. Farooq Æ S. M. A. Barsa Department of Crop Physiology, University of Agriculture, Faisalabad 38040, Pakistan A. Wahid (&) Department of Botany, University of Agriculture, Faisalabad 38040, Pakistan e-mail: [email protected]

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 physiological 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 deleterious effects on the soil environment for the succeeding wheat and other upland crops. Puddling requires an excess of water at a time when the reservoirs are low. Late onset of monsoon and drudgery of operations often delay rice transplantation, which leads to late vacation of fields, forcing the sowing of wheat when the appropriate time has passed. Furthermore, in view of the

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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 growing 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 integrated (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 performed in a single cycle of wetting and drying (Lee and Kim 1999). Until recently, Farooq et al. (2006b) introduced a new technique of osmohardening 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

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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 producing 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 physiological enhancements of direct-seeded rice (Du and Tuong 2002; Ruan et al. 2002), no comprehensive study has evaluated the response of wideranging seed priming treatments for enhancing seedling establishment, plant allometry or the quality of harvested paddy. Information is also scarce on the physiological implications of priming-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

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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 randomized complete block design (RCBD) with three replications. Seed priming treatments, chosen from the previous experience (Basra et al. 2005; Farooq et al. 2005, 2006a, b), were: (a) hydropriming, soaking seed in aerated distilled water for 48 h, (b) hardening, soaking seeds in tap water at 27C ± 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) osmohardening, 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 receiving no prior treatment. Primed seeds were given three washings with water and re-dried closer to original moisture (ca. 8%) under forced air at 27C ± 3 (except for pre-emergence). These seeds were put in polythene bags and stored in a refrigerator at 5 ± 1C until used. Seed sowing and agronomic practices Field soil was sandy clay loam with pH 8.1, electrical conductivity 0.30 dS m–1 and organic matter 0.75%. Land was ploughed five times with tractor drawn implements to achieve the required seedbed. Fertilizer was applied as urea (46%), single superphosphate (18% P2O5), sulphate of potash (50% K2O) and ZnSO4 (35% Zn) at recommended 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

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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 physiological 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 harvested 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 4C. 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 distilled water and left for 24 h at 25C (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 panicle 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

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a

(a)

b

10

α-Amylase activity (units)*

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 (multiplied 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).

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c e

f

d

8 6 4 2 0 20

Statistical analysis

a

Results Characteristics of primed seeds Priming treatments increased the a-amylase activity of kernels, which was in the order: KClosmohardening > pre-germination > CaCl2-osmohardening > hardening > ascorbate priming > hydropriming > 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 increased a-amylase activity and soluble sugars content (Fig. 2).

-1

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.

Soluble sugars (mg g fresh weight)

(b) b

b

16

b c

d

12

e 8

4

0

Seed priming treatments Fig. 1 Effect of seed treatments on (a) a-amylase activity and (b) total soluble sugars in direct-seeded coarse rice. *One unit of the enzyme’s activity is the amount of enzyme which released 1 lmol of maltose by 1 ml original enzyme solution in 1 min. , control; , pre-germinated; , hydropriming; , osmohardening (KCl); , osmohardening (CaCl2); , ascorbate priming; , hardening

and ascorbate primed, whilst the reverse trend for these attributes was evident in pre-germinated and controls (Table 1).

Germination and seedling establishment Agronomic characters and yield components 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 osmohardened with KCl followed by CaCl2, hardened,

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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

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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 ascorbate priming (Table 4). Inverse but close associations were noted of MET with kernel yield (Fig. 3b) and harvest index (Fig. 3c), reflecting the specific effects of priming on these attributes.

Fig. 2 Relationship between a-amylase activity and total sugars in direct-seeded coarse rice as affected by different seed priming treatments. *One unit of the enzyme’s activity is the amount of enzyme, which released 1 lmol of maltose by 1 ml original enzyme solution in 1 min

Allometry

in plants from KCl- and CaCl2-osmohardening treatments followed by hardening and ascorbate priming (Table 2). A positive correlation was noted between MET and days to heading (Fig. 3a). Priming treatments produced significant differences in most of the growth and yield attributes. Plants originating from control and pre-germination 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 recorded 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

Table 1 Effect of seed priming on the seedling establishment of directseeded coarse rice

Treatment means ± standard error. Means sharing same alphabets differ nonsignificantly

Regardless of seed priming treatments, values of all derived growth attributes were greater at midharvest, compared to others, displaying maximal growth and dry matter production early at physiological maturity. Priming treatments improved LAI at all harvests, KCl-followed by CaCl2osmohardening, and ascorbate priming (Fig. 4). Likewise, osmohardening with KCl and CaCl2 maximally 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

Treatments

Days to start Mean emergence Days to 50% Final emergence of emergence time (days) emergence (%)

Control Pre-germination Hydropriming Osmohardening (KCl) Osmohardening (CaCl2) Ascorbate priming Hardening

4 4 3 2 3 3 3

± ± ± ± ± ± ±

0.3a 0.3a 0.3b 0.3b 0.4b 0.4b 0.3b

6.6 7.0 6.0 4.7 5.2 5.9 4.9

± ± ± ± ± ± ±

0.2b 0.2a 0.2c 0.2e 0.2d 0.3c 0.3e

5.3 5.6 4.3 4.0 4.3 4.8 4.4

± ± ± ± ± ± ±

0.8a 0.6a 0.9ab 0.9b 0.8b 0.7ab 0.8b

80 80 85 88 88 82 84

± ± ± ± ± ± ±

2.1d 2.1d 1.9b 2.0a 2.3a 2.4c 2.5bc

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Table 2 Effect of seed priming on days to heading and maturity of direct-seeded coarse rice Treatments

Emergence to heading days

Heading to maturity days

Control Pre-germination Hydropriming Osmohardening (KCl) Osmohardening (CaCl2) Ascorbate priming Hardening

92 96 85 79

34 34 29 24

± ± ± ±

6a 5a 6b 6c

± ± ± ±

2a 2a 2b 2cd

81 ± 5bc

26 ± 2bcd

85 ± 6bc 81 ± 6bc

27 ± 2b 25 ± 2cd

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

chalky kernels. Osmohardening with KCl and CaCl2 followed by ascorbate priming and hardening produced lower numbers of spikelets and kernels with the above-mentioned characters, whilst this number was greater in the case of pregermination 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 characteristics 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

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

between seed vigor and field performance of rice (Yamauchi and Winn 1996). Furthermore, seed priming produces more vigorous, faster, and uniform 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

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

Plant height No. of tillers No. of fertile 1000 kernel Straw yield Kernel yield Harvest index tillers (m–2) weight (g) (kg m–2) (kg m–2) (%) (cm) (m–2)

Control Pre-germination Hydropriming Osmohardening (KCl) Osmohardening (CaCl2) Ascorbate priming Hardening

82 80 85 85 88 82 84

± ± ± ± ± ± ±

0.5bc 4.3c 5.0ab 4.6ab 4.3a 4bc 4.6abc

623 676 738 729 656 706 713

± ± ± ± ± ± ±

58b 55bcd 63a 58ab 57cd 63abc 65abc

584 574 659 658 628 643 611

± ± ± ± ± ± ±

4.2d 5.2d 16.2a 14.2a 13.9b 12.6ab 17.2c

16.3 ± 2b 15.3 ± 2b 16.7 ± 2b 19.0 ± 1a 16.3 ± 2b 16.7 ± 2b 17 ± 2ab

0.81 0.80 0.84 0.90 0.89 0.89 0.90

± ± ± ± ± ± ±

0.02c 0.01c 0.02a 0.02b 0.02b 0.09b 0.03b

0.27 0.26 0.28 0.32 0.31 0.30 0.30

± ± ± ± ± ± ±

0.09d 0.09de 0.08d 0.08a 0.09b 0.09c 0.09c

24.0 24.5 24.8 26.3 25.8 25.3 25.3

± ± ± ± ± ± ±

0.2f 0.2e 0.2d 0.2a 0.2b 0.3c 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

Sterile spikelets (%)

Opaque kernels (%)

Abortive kernels (%)

Chalky kernels (%)

Normal kernels (%)

Kernel protein (%)

Kernel amylose (%)

Kernel water absorption ratio

Control Pre-germination Hydropriming Osmohardening (KCl) Osmohardening (CaCl2) Ascorbate priming Hardening

7.1 7.3 6.9 5.5

18.7 17.7 18.0 15.3

2.4 2.4 1.9 1.5

27.0 26.0 25.7 20.6

51.9 54.7 54.4 55.5

6.6 6.5 6.9 7.4

31.3 31.5 31.3 28.1

3.3 3.1 3.3 3.7

± ± ± ±

0.1b 0.1a 0.2c 0.2f

± ± ± ±

2.2a 2.2abc 2.2ab 2.3d

± ± ± ±

0.05a 0.05a 0.05b 0.05e

± ± ± ±

0.6a 0.6b 0.6b 0.6e

± ± ± ±

8.8b 9.1ab 9.7ab 9.5ab

± ± ± ±

0.2d 0.3d 0.3c 0.3a

± ± ± ±

0.4a 0.4a 0.4a 0.4c

± ± ± ±

0.1c 0.1d 0.1c 0.1a

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

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

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

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 performance 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 (Table 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 establishment 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 produce 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

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

production of more vigorous seedlings. Previous studies showed that seed priming in rice seedlings led to more uniform, vigorous, and faster emergence of seedlings, bestowing wide-ranging phenological 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 assess time course changes in growth and dry matter accumulation (Niklas 1994). Improved LAI,

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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 emergence 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 comparisons 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 potassium (Thakuria and Choudhary 1995). Seed priming with KCl and CaCl2 improved kernel quality characteristics in osmoprimed directseeded 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 osmohardening 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 proteins and the negative one of amylose with water absorption ratio (Fig. 5a,b) are plausible justifications for better kernel quality. In crux, these findings strongly suggest that seed priming is a pragmatic strategy in directseeded 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 seedlings, better plant growth, allometry, yield attributes, 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

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

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 Education Commission, Government of Pakistan, is acknowledged.

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