Effect of seed size and genotype on germination characteristic and seed nutrient content of wheat

In order to study the effects of seed size and genotype on nutrient uptake and growth characteristic of wheat, a field experiment was conducted in a split plot randomized block design with genotypes as main plots and seed size as subplots, with four blocks at the Roseworthy Campus, the University of Adelaide in 2010. Two experiments were designed (1) a laboratory experiment with seeds germinated in wet filter paper for 14 days to determine coleoptile length (2) a pot experiment with three harvest times to determine the effect of seed size and genotype on seedling vigor, the relation between seed nutrient content. The wheat genotypes used were Burunga, Excalibur, Janz, Machete, RAC655, Trident, Spear, Tatiara, Yarralinka (Triticum aestivum L.) and Yallaroi (Triticum durum). Obtained results showed that genotype and seed size had significant effect on total nutrient content, coleoptile length, emergence efficiency and root and shot dry matter production. Tatiara had more amount of Fe, Cu and K concentration in wheat seed among all genotype. Maximum amount of B, Mn, Mg and Na were observed in Janz, Yarralinka, Machete and Yallaroi. Among all genotype, large coleoptile length was recorded in Spear and small of it was observed in Yallaroi and among seed sizes large seeds had maximum amount of coleoptile length. Tatiara, Exculibur, Spear and RAC655 had a significantly greater seedling growth (shoot and root) compared to other genotype. Plant grown from large seeds compared to those grown from small seeds was more vigorous and produces greater dry matter for all genotypes.


INTRODUCTION
Rapid seedling establishment is an important requirement for successful crop production in dryland farming systems.Seed size, as a characteristic of seed quality, influences seedling growth and establishment.Studies of the relationship between seed size and early growth have been reported since early this century (Zavits, 1908).Seedling establishment and speed of emergence influence the time required for seedling to reach the autotrophic phase.Most investigators have reported a positive relationship between seedling vigor, improved stand establishment and higher productivity of cereal crops with plants originating from large seed compared to those grown from smaller seed.Chastin et al. (1996) suggest that larger seeds produce seedlings with greater *Corresponding author.E-mail: Mahdi_bbn@yahoo.com.
early growth and increased competitive ability against weeds and pests.Amico et al. (1994) concluded that higher vigor that occurred in larger seed is due to the larger food reserves in these seeds.They also noted a positive linear relationship between seed weight and emergence in the field.Baalbaki and Copeland (1997) reported that in wheat, seed size not only influence emergence and establishment but also affected yield components and ultimately grain yield.A similar observation was made by Arunachalam et al. (2003), while working with the tree species, and this was attributed to the larger food reserves in the larger seeds.These results also are in conformity with Singh (2003) in wheat.Also, these results indicated that seed size had greater effect on percent than index of germination and emergence.With increased seed size, higher germination and emergence were determined in triticale (Kaydan and Yamur, 2008), but besides higher germination percentage declined median germination time were determined in some forage plants (Larsen and Andreasen, 2004).In another study, Willenborg et al. (2005) stated that germination was increased with increasing seed size in oat (Avena sativa L.).In pea (Pisum sativum L.) it was showed that cultivars with low 100 seed weight had higher germination percentage than larger seed ones (PekÕen et al., 2004).The superior germination of larger seed is ascribed to a greater amount of endosperm reserves that are available during the germination process (Schmidt, 2000).The possible effect of seed size on germination is associated with the length of the structures that form the seedling, but not necessarily with the subsequent biochemical conversion of storage reserves into germinating tissues (Soltani et al., 2002).Nerson (2002) showed that small muskmelon seeds had the lowest percentage germination, emergence, and the lowest seedling growth demonstrating that there is an association between seed physical parameters and seed quality.Seed size plays a major role in germination and establishment of vigorous seedlings that is essential to achieving high yield.
The experiments are designed to investigate the relative effects of seed character on seedling vigor in wheat varieties in South Australia.

MATERIALS AND METHODS
The experiment was conducted in a split plot randomized block design with genotypes as main plots and seed size as subplots, with four blocks at the Roseworthy Campus, the University of Adelaide in 2010.Two experiments were designed (1) a laboratory experiment with seeds germinated in wet filter paper for 14 days to determine coleoptile length and (2) a pot experiment with three harvest times to determine the effect of seed size and genotype on seedling vigor and seed nutrient content.Ten wheat genotypes were selected from the wheat breeding programs of the University of Adellide.The wheat genotypes used were Burunga, Excalibur, Janz, Machete, RAC655, Trident, Spear, Tatiara, Yarralinka (Triticum aestivum L.) and Yallaroi (Triticum durum).Seed was collected for all genotypes from Kapunda, South Australia, in 2010 for use in the glasshouse.Seeds were graded into three groups by sieving, namely large (>2.5 mm diameter), medium (2.25 to 2.5 mm) and small (1.9 to 2.25 mm) for each genotype.In laboratory experiment, seeds of each group and each genotype were surface sterilized using hypochlorite solution (3%v/v) for 30 s, followed by washing three times with distilled water.Rectangular filter paper (Ekwip, 46 × 23 cm) was marked 15 cm from the bottom of the long side and soaked for a few seconds in distilled water.Twenty seeds were placed along this mark with the embryo facing the base of filter paper.The filter paper was rolled and covered with aluminum foil to prevent drying out and to exclude light, and was placed with embryo facing downwards in a container and kept for 12 to 14 days at 15°C in the dark until coleoptiles elongation had stopped.This was determined by monitoring some test papers until the first leaf have protruded from the tip of the coleoptile.The final lengths of the coleoptile were measured with a ruler.This technique is used for determining germination and coleoptile lengths in seed certification tests in South Australia (K.Boyce, personal communication, 1994).In pot experiment, fifteen seeds of each seed size of each genotype were weighed and sown at 5 cm depth in plastic pots (15 cm diameter).Each pot contained 1.7 kg of UC (University of California) standard soil.Pots were watered every other day to prevent water stress.Pots were kept in the same conditions in glasshouse at 24 ± 4 and 10 ± 4°C (day/night) with an average relative humidity of 60% and approximately 14 h day length.Plants were thinned to 10 seedlings per pot after emergence.Shoots were cut 1 cm from the soil surface, and roots were washed free of soil under running tap water.For measuring seed nutrient content, seed samples were washed, oven dried, ground and extracted with wet acid digestion method and analyzed for elemental content by atomic absorption spectrophotometer, model-2380 (Jones and Case, 1990).
All data were analyzed using the SUPER ANOVA statistical computer program.Means were compared using the LSD (P < 0.05).

Seed nutrient content
Result in Table 1 showed genotype had significant effect on total concentration of Fe, Cu, B, Mn, Ca, Mg, Na, K and P in wheat seeds and there was no significant effect on concentration of Zn and S. Tatiara seed contained very high concentration of Fe compared to other genotypes and minimum amount of Fe was recorded in Janz.High amount of B was obtained in Jaze and minimum amount of B was recorded in Trident seeds.The concentration of Cu was significantly higher in Tatiara and lower in machete, RAC655 and Jans with average of 6.08, 4.76, 4.96 and 4.97 mg/Kg, respectively.Higher amount of Mn concentration was obtained in Yarralinka seeds (40 mg/Kg) and lower of it was observed in Yalloari (31.02 mg/Kg).Yallaroi, durum wheat, had a much higher concentration of Na, K and P in the seed in comparism with other genotypes with mean of 71.8 mg/ Kg, 5.15 g/Kg and 3.04 g/K, respectively but lower amount of Na, K and P concentration was recorded in Trident, Baronga and Janz with mean of 25.4, 3.90 and 2.26, respectively as shown in Table 1.Obtained results in this part showed that seed size had significant effect on seed concentration of Cu, Mn, Zn, Ca, Na, K and P, but there was no significant effect on concentration of Fe, B, Mg and S. High amount of Cu, Mn, Zn, and P was observed in large seed with main of 5.72, 38.4,21.1 mg/Kg and 2.82 g/Kg while maximum amount of Na and K were obtained in small seed with mean of 38.4 Mg/Kg and 4.82 g/Kg, respectively.The concentration of other nutrients tended to be lower in the medium sized seed than both of the large and small seeds as shown in Table 1.

Coleoptile length
Coleoptile length was significantly affected by genotype and seed size, but the interaction between these two factors was not significant.Among 10 genotypes, Spear produced the longest coleoptiles (91 mm) compared with 69 mm for Janz and 62 mm for Yallaroi.Excalibur and Trident were in the middle of the range for coleoptile  length.Similar results were found by Cornish and Hindmarsh (1988) in wheat.They concluded that differences in inherent grain size between genotypes did not explain the differences in coleoptile length (Figure 1).

Emergence efficiency (EE) or speed of emergence
Emergence efficiency (EE) or speed of emergence was significantly affected by genotype (P≤0.05).Trident, Exculibur and Barungare presented a group of genotypes with somewhat better EE than other genotypes.Bread wheat Yarralinka and durum wheat Yallaroi had the lowest EE.The ten wheat genotypes can be classified into three classes for speed of emergence.Trident, Excalibur and Barunga was found to be the fastest class, Spear and RAC655 in a middle class and Janz, Machete, Tatiara, Yarralinka and Yallaroi in a slowest class (Figure 3).

Shoot and root dry matter production
Shoot and root growth was affected by genotype in all  three harvests time.At harvest, 1 and 2, Tatiara, Exculibur, Spear and RAC655 had a significantly greater seedling growth (shoot and root) compared to Yarralinka and Yallaroi as shown in Table 2. Seed size had significant effect on shoot and root dry matter production.plant grown from large seeds compared to those grown from small seeds were more vigorous and produces greater dry matter for all genotypes (Tables 2 and 3).Large seed produces more shoot and root dry matter in all three harvests.The interaction of genotypes and seed size was significant for shoot growth at harvest 1 and root production at harvest 2. Differences in initial seed weight had a pronounced effect on the vegetative characteristic of 10 wheat genotypes in glasshouse experiments (Table 2).

DISCUSSION
Both genetic and environmental factors affect seed size (Primackand Autonomics, 1981).Temperature, nutrient and water availability are some of the factors affecting Nik et al. 2023

Emergence efficiency (%)
Figure 3.Effect of wheat genotype on emergence efficiency of wheat.
final seed weight.Assuming that seed size is limited either directly by the availability of resources or current photosynthesis, it is not surprising that seed size should be reduced in conditions of reduced nutrients or water availability or different season, since both these factors affect photosynthetic rates and finally seed size.Results showed that there was difference among wheat genotype in seed nutrient content and some of genotypes had more amount of seed nutrient content than other genotype.Some of wheat genotype had a high growth and high dry matter production in contrast with other genotype.The genotype with high dry matter production accumulates more seed nutrient (Cu, Mn, Zn, Ca, Na, K and P) (Marschner, 1995).Obtained result in this research showed that coleoptile length was highly correlated with seed size.Large seed produced longer coleoptiles than small seed (Figure 2).This suggests that the use of large seed for deep sowing 2024 Sci.Res.Essay provides not only extra seed reserves for emergence but also long coleoptile to allow the successful utilization of those reserves (Radford, 1987).Environmental factors also affect coleoptile length, including soil type, soil strength, surface crusting, light penetration, crop residue, source of seed and temperature.Nebreda and Parodi (1977), working with three triticale genotypes, found that coleoptile derived from large seeds were significantly longer than those from ungraded seed and small seeds; the last group always producing the shortest coleoptile.Cornish and Hindmarsh (1988) reported that within cultivars and size effects on coleoptile length were statistically significant but that this was a relatively small source of the total variation for coleoptile length.
Compared to plants derived from small seeds, those from large seeds were more vigorous as indicated by greater increases in dry matter under glasshouse conditions.Plants grown from large seeds produced more shoot and root dry matter than plants grown from small seed and subsequently more grain yield under field conditions.Reis and Everson (1973) found the same in that in wheat large seeds produced larger seedling in glasshouse conditions.Tomer and Maguire (1990) stated that the effect of seed vigor on grain yield is dependent on the environment.Thus, low plant populations which may result from low seed vigor may not influence yield under good soil conditions, but may cause significant yield loss when conditions are suboptimal.This conclusion is supported by the earlier observation that dry matter production of plant grown from large seeds was always significantly greater than plants grown from small seed.The larger root system of seedling grown from larger seeds may be useful in maintaining water availability under a limited soil moisture supply, especially during early growth when surface soil may often be drier than subsurface soil.Later in the season, when moisture is limited, larger root systems produced from large seed explore more of the soil to extract more soil moisture without accompanying increases in transpiration and this may contribute to higher grain yield under limited soil moisture conditions (Mian and Nafziger, 1994).This probably accounts for the better seed size and hence grain yield of the plots sown with large seed.

Conclusion
It may be concluded from this experiment that positive relation was found among large seed grade and genotype in all characteristic of wheat that are investigated in this research.The research revealed that large seeds had high amount of nutrient content such as, Mn, Zn, Cu and Ca. while maximum amount of Na, K and P was observed in small seeds.Among all genotype, large coleoptile length was recorded in Spear and small of it was observed in Yallaroi and large seeds had maximum amount of coleoptile length.Tatiara, Exculibur, Spear and RAC655 had a significantly greater seedling growth (shoot and root) compared to all wheat genotype that measured in this experiment.Other result in this investigation showed plant grown from large seeds compared to those grown from small seeds were more vigorous and produces greater dry matter for all genotypes.These data support the hypothesis among of all wheat genotype in this experiment, Trident was the best in emergence efficiency that was measured compared to other genotypes but most coleoptile length was recorded in Spear and that large seeds have superior performance to small seeds.

Figure 1 .
Figure 1.Effect of wheat genotype on coleoptile length.

Figure 2 .
Figure 2. Effect of seed size on coleoptile length.

Table 1 .
Effect of genotype and seed size on total nutrient content of wheat seeds.

Table 2 .
Effect of genotype and seed size on shoot dry matter production at 14 days in ten wheat genotype (glasshouse experiment).

Table 3 .
Effect of genotype and seed size on shoot and root in wheat in glasshouse experiment.