Effect of seed and embryo size on early growth of wheat genotypes

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1 African Journal of Microbiology Research Vol. 5(27), pp , 23 November, 2011 Available online ISSN Academic Journals DOI: /AJMR Full Length Research Paper Effect of seed and embryo size on early growth of wheat genotypes Mohsen, Moussavi Nik 1, Mahdi, Babaeian 2 and Abolfazl, Tavassoli 2 1 Department of Agriculture, Zabol University, Zabol. Iran. 2 Department of Agriculture, Bojnourd Branch, Islamic Azad University, Bojnourd. Iran.. Accepted 6 October, 2011 Rapid seedling establishment is an important requirement for successful crop production in dry land farming systems. Seed size, as a characteristic of seed quality, influences seedling growth and establishment. In order to study the effects of seed and embryo size on early growth of wheat genotypes 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 Rose worthy Campus, the University of Adelaide in Two experiments are described; the first experiment was design to correlate the size of embryo with seed size for different genotypes of wheat. The second was a pot experiment conducted for 14 days to ascertain the effect of embryo size on seedling vigor. The result showed that Barunga, Excalibur and RAC655 had similar Embryo weights in large and medium seed, but in other wheat genotypes large seed had heavier Embryos than medium seed and large seed had 42% heavier than small seed. Between genotypes, Yallaroi and Spear had heavier embryos than most other genotypes at all seed sizes and Janz had relatively small embryos in the large seed. Large embryos produced longer coleoptile than small embryos. Between genotypes, Spear had the longest and Yarallinka the shortest coleoptile and there was no interaction between genotypes and embryo size for coleoptile length. Greater seedling dry matter resulted from large seed compared to medium and small seed, except in Tatiara which had similar seedling dry matter when grown from large and medium seed. Generally the result in this experiment showed that, seedlings from large seed have better growth than those from small seed. Key words: Wheat, seed size, embryo, coleoptile, seedling growth. INTRODUCTION In Southern Australia, the top soil may contain sufficient moisture at sowing to sustain crop growth, but this moisture can be lost quickly where ground cover is insufficient to prevent moisture evaporation from the seed-bed. Australia, are considered severely deficient in micronutrients for growth of wheat, oats (Avena sativa L.), or barley (Hordeum vulgare L). The native vegetation in this area is fully adapted to these soils mainly due to their slow growth rate. The difference in nutrient uptake and utilization may be associated with better root geometry, ability of plants to take up sufficient nutrients from lower or subsoil concentrations, plants ability to solubilize nutrients in the rhizosphere, better transport, *Corresponding author. mahdi_bbn@yahoo.com. distribution and utilization within plants and balanced source-sink relationships. Crop physiology and management studies often describe and quantify the changes plant breeders and geneticists have delivered in new germplasm but rarely address the specific changes needed to advance crop establishment, yield potential, or other agronomic goals (Snape, 2001). In wheat, seed size is positively correlated with seed vigour: larger seeds tend to produce more vigorous seedlings (Cookson et al., 2001). Similarly Khah et al. (1989) found that low-vigour spring wheat seed produced lower yields only when it resulted in low plant populations or when planting was later than normal. Many reports suggest that larger seeds produce seedlings with greater early growth and increased competitive ability against weeds and pests (Chastin et al., 1995; Douglas et al., 1994; Mian and Nafziger, 1992). Plants grown from small seeds emerged

2 4860 Afr. J. Microbiol. Res. faster but accumulated less shoot dry weight than plants grown from large seeds. There was no cultivar by seed size interaction observed for speed of emergence and seedling shoot dry weight. Seed size, speed of emergence all contributed to differences between cultivars in seedling vigour. Seed size accounted for approximately 50% of the variation in seedling shoot dry weight. It was concluded that selecting for seedling vigour could be done by selecting for seed size, speed of emergence and rate of plant development (Lafond and Baker, 1986). As such, plants derived from large seed appear to have greater vigour and are able to acquire a larger share of plant growth factors relative to plants derived from small seed (Robert and Stogarda, 2004). Use of large seed size and increased seeding rates can improve wheat competitiveness and provide an effective means to reduce wild oat biomass and seed production (Qingwu and Robert, 2002). Willenborg et al. (2005) reported that germination characteristics were affected by cultivar, seed size and moisture stress in six western Canadian oat genotypes. They also reported that large oat seed had greater final germination that resulted in better stand establishment, particularly where low spring soil moisture limits stand establishment than that of small seed. With increased seed size higher germination and emergence were determined in pearl millet (Kawade et al., 1987) and 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). Addae and Pearson (1992) reported positive relationships between seed size and coleoptile length in wheat. Amico et al. (1994) also concluded that higher vigor that occurred in larger seed is due to the larger food reserves in these seeds. These results also are in conformity with Singh and Singh (2003) in wheat. 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. Early vigor in crops lead to better moisture conservation because plants cover the soil more quickly, thus reducing evaporation from soil surface. The crops capacity to quickly provide effective ground cover can be especially important in dry land farming regions. Generally as shown, seed size is a crucial factor determining the emergence, establishment and final yield of annual crops. The experiment were design to investigate (i) whether there is a relationship between seed size and embryo size, (ii) weather wheat genotypes differ in embryo size, and (iii) whether embryo size can influence early seedling vigor of wheat. 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 Rose worthy Campus, the University of Adelaide in Two experiments are described; the first experiment was design to correlate the size of embryo with seed size for different genotypes of wheat. The second was a pot experiment conducted for 14 days to ascertain the effect of embryo size on seedling vigor. Embryo measurement Ten seeds from 10 genotypes and three seed size were soaked in distilled water for 12 h at 20 C. Seed length was measured along the long axis, the embryo was then excised using a scalpel under a microscope and the length of embryo measured using an ocular scale in the right eyepiece. Embryos were then dried at 30 C for 12 h and weighted. Seedling vigor experiment Plastic pots 15 cm in diameter were filled with about 2 kg of UC soil. Each pot was divided into three equal sectors by using hard plastic partitions (30 10 cm). Seeds were surface-sterilized, pregerminated at 20 C and 80% humidity in the dark for 24 h five pregerminated seeds from each genotype and each seed size were sown 2.5 cm depth in each sector of a pot. Pots were located in a glasshouse with temperature and light as in the external environment. Black polyethylene beads were added to the soil surface to reduce evaporative water loss. Pots were watered to the field capacity every day. After 10 days, the width and length of the second leaf of each established seedling were measured and leaf area calculated as though the leaf was a rectangle. Plants were harvested 14 days after sowing, dried at 80 C for 24 h and seedling dry matter (shoot + root) was determined. The experiment was set up in a split-plot with genotype as the main plot (pot) and embryo size as subplots (10 genotypes three seed size) with four replicates. Results were analyzed SUPER ANOVA computer program. RESULTS Relationship between seed size and embryo size Seed weight and embryo size Embryo size depended on interaction of seed size and genotype (Table 1). Barunga, Excalibur and RAC655 had similar embryo weights in large and medium seed, but in other wheat genotypes large seed had heavier embryos than medium seed. Generally, large seed had 42% heavier than small seed. Between genotypes, Yallaroi and Spear had heavier embryos than most other genotypes at all seed sizes. Janz had relatively small embryos in the large seed. Except for the fact that there was not a significant interaction between genotypes and seed size for embryo length, the overall results closely mirrored those for embryo size (Figures 1 and 2). The ratio embryo to seed weight depended on seed size and genotype as well as their interaction (Table 1). The

27 Excalibur 530 520 260 1.27 1.77 1.31 Janz 380 250 230 0.93 0.92 1.49 Machete 480 350 250 1.14 1.18 1.23 RAC655 530 470 220 1.04 1.57 0.88 Spear 650 520 270 1.39 1.66 1.

3 Nik et al Table 1. The effect of genotype and seed size on embryo characters in wheat Embryo weight (ug) Embryo W/ seed W (%) Genotype Seed size Seed size L M S L M S Barunga Excalibur Janz Machete RAC Spear Tatiara Trident Yarralinka Yallaroi LSD 5% (G SS) G, genotype; SS, seed; W, weight; L, large x > 2.5; M, medium, 2.5 > x > 2.25; S, small 2.25 >x > 1.9 mm diameter. Figure 1. The effect of genotype on embryo length. Figure 2. The effect of seed size on embryo length.

4 4862 Afr. J. Microbiol. Res. Figure 3. Regression of embryo characters of wheat on seed weight (10 genotype 3 seed classes). Table 2. Genetic difference for some plant parameters in wheat. Genotype Coleoptile length (mm) Second leaf width Second leaf length (mm) Barunga Excalibur Janz Machete RAC Spear Tatiara Trident Yarralinka Yallaroi LSD 5% Table 3. The effect of seed size on some plant characters of wheat. Characters Seed size Large Medium Small LSD 5% Coleoptile length (mm) Leaf width (mm) Leaf length (cm) interaction between seed size and genotypes was highly significant in this experiment. The ratio was higher in small seed than in large seed, except for Yallaroi, Excalibur and Spear. These three genotypes had a higher ratio, while the ratio was low in Trident and Janz. Excalibur, Spear and RAC655 had higher ratios in medium and small seed. In contrast, Janz, Yarralinka and Yallaroi showed the highest ratio in small (Table 1). Machete was unusual in that the ratio did not change across seed sizes. Combining all data across genotypes the correlations between seed weight with embryo length and embryo weight were r=0.71, respectively (Figure 3 a,b). Embryo size and plant growth Coleoptile Large embryos produced longer coleoptile than small embryos. Between genotypes, spear had the longest and Yarallinka the shortest coleoptile (Tables 2 and 3). There

5 Nik et al Figure 4. Relationship between seedling growth characters and seed embryo size in wheat (10 genotype 3 seed size). was no interaction between genotypes and embryo size for coleoptile length. The simple correlations between embryo length and weight with coleoptile length were highly significant (r=0.81 and 0.65, respectively) (Figure 4). Leaf measurement The width of the second leaf was influenced by embryo size and genotype effects (Tables 2 and 3). Large seed and large embryos are produced wider leaves. The leaves of Tatiara, Mechete and RAC655 were wider than those of other genotypes. Janz had the narrowest leaves. There were no significant interactions between genotype and embryo size on leaf width. Similarly, leaf length was influenced by embryo size and genotype and there was no interaction between them. Large seeds that are large embryos produced longer leaves than seed of medium and small embryos (Table 3). Embryo size and genotype significantly influenced leaf area (Figures 5 and 6). Among genotypes, Mechete, RAC655, Tatiara and Yarralinka had larger leaf areas than Janz. The interaction of embryo size and genotypes was not significant. Relationship between shoot and shoot dry matter with embryo size and root dry matter production measured at 14 days after sowing were plotted against embryo length and embryo weight. Significant positive

4864 Afr. J. Microbiol. Res. Figure 5. Deference between wheat genotype in the leaf area of the second leaf. Figure 6. The effect of seed size on the area of second leaf.

Greater seedling dry matter resulted from large seed compared to medium and small seed, except in Tatiara which had similar seedling dry matter when grown from large and medium seed (Table 4).

6 4864 Afr. J. Microbiol. Res. Figure 5. Deference between wheat genotype in the leaf area of the second leaf. Figure 6. The effect of seed size on the area of second leaf. correlations were found (Figure 4). Seedling dry weight Genotype, seed size and the interaction of these treatments were significant for seedling dry matter. Greater seedling dry matter resulted from large seed compared to medium and small seed, except in Tatiara which had similar seedling dry matter when grown from large and medium seed (Table 4). In the medium seed, no difference was observed between genotypes for seedling dry matter. In contrast, in large and small seed size there were differences between genotypes. For example, Exculibur and Janz. The correlation of embryo length or weight with seedling dry matter was r=0.78 and 0.71, respectively (Figure 4 g-h). DISCUSSION The result showed that, generally, seedlings from large seed have better growth than those from small seed. This experiment suggests that the initial size of the meristematic tissue (embryo) in the seed, which is positively correlated with seed weight, is at least part of the reason for this phenomenon. There was a wide range of variation for embryo size between the wheat genotypes studied (Table 1 and Figure 1) did not always follow seed weight. For instance, RAC655 produced heavier seed than spear, but the spear had the larger embryo. Thus there is genetic variability for embryo size over that for seed size alone. Embryo weights of small seeds varied between 39 to 58% that of large seeds between wheat genotypes. Variation is seedling attributes was associated with differences in the embryo size. Embryo weight had a positive effect on coleoptile length, leaf width, leaf length, leaf area of second leaf and seedling dry matter at a level to be of a practical significance (Figure 6, Tables 3 and 4). Genotypes with greater embryo weight produced longer coleoptiles. Embryo length was better correlated with coleoptile length than embryo weight. Amongst the genotypes, it would seem that spear`s large embryo is an important attribute contributing towards the good seedling vigour of this genotype. A balance between the embryo and the

7 Nik et al optimum endosperm is, however, to be maintained for both crop establishment and milling quality. Such effect of embryo and endosperm size on seedling growth can be explained by the fact that large embryos would have more embryonic cells to initiate growth, while a larger endosperm would lead to higher supply of energy for germination and subsequent growth of the seedling. In this study embryo size was highly and positively correlated with seedling dry matter. Another potential difference between large seed and small seed, apart from carbohydrate reserve and embryo size, is differences between seed content of other nutrient such as protein or trace elements. Such differences could occur if there is disproportionate accumulation in different seeds on the mother plants. Across genotypes, large seeded genotypes do not always have large embryos, so it should be possible to select for seed size and embryo size independently. The genetic variation show in this experiment for embryo size would influence the probability of achieving good crop establishment which could then lead to greater crop yields. Adoption and pursuit of objective in plant breeding depends upon the important of attribute under consideration, that adequate genetic variability and that there is a means by which the attribute can be measured. From this experiment embryo size seems to be an attribute which could contribute to grain yield and adaptation; genetic variation in embryo size exists from which to breed and select. However, the actual measurements of embryo weight as total weight is too time consuming and subject to seed size variation within a cultivar to be attractive to breeders. Embryo length was closely correlated with embryo size; it can be measured quickly and easily on whole grain and is possibly more precise. In fact correlation between embryo length and seedling parameters was better than those for embryo weight. The embryo length as an index of embryo size could easily be used by breeders wishing to select for embryo size and subsequent seedling vigour. Care should be taken when breeding and selecting for embryo size to take notice of overall grain conformation and shape. Protruding embryos, particularly a radical protruding beyond the tip of a wheat seed could render it liable to physical damage during harvesting, seed processing and seedling operation. REFERENCES Chastin TG, Ward KJ, Wisocki DJ (1995). Stand establishment responses of soft white winter wheat to seedbed residue and seed. Crop Sci., 35: Cookson WR, Rowarth JS, Sedcoli JR (2001). Seed vigour in perennial ryegrass (Lolium perenne L.) effect and cause. Seed Sci. Technol., 29: Douglas CLJ, Wilkins DE, Churchill DB (1994). seed size and seed density effects on performance of soft whit winter wheat. Agron. J., 86: Kawade RM, Ugale SD, Patil RB (1987). Effect of seed size on germination, seedling vigor, and test weight of pearl millet. Seed Res., 15: Kaydan D, Yağmur M (2008). Germination, seedling growth and relative water content of shoot in different seed sizes of triticale under osmotic stress of water and NaCl. Afr. J. Biot., 7: Khah EM, Robert EH, Ellis RH (1989). Effects of seed aging on growth and yield of spring wheat at different plant population densities. Field Crops Res., 20: Larsen SU, Andreasen C (2004). Light and heavy seeds differ in germination percentage and mean germination thermal time. Crop Sci., 44: Mian AR, Nafziger ED (1992). Seed size effects on emergence, head number and grain yield of winter wheat. J. Prod. Agric., 5: Nerson H (2002). Relationship between plant density and fruit and seed production in muskmelon. J. Am. Society Hortic. Sci., 127(5): Qingwu X, Robert NS (2002). Spring wheat seed size and seeding rate affect wild oat demographics. Weed Sci., 50(3): Robert N, Stougarda QX (2004). Spring wheat seed size and seeding rate effects on yield loss due to wild oat (Avena fatua) interference. Weed Sci., 52(1): Singh, Singh (2003). Seed size and adventitious (nodal) roots as factors influencing the tolerance of wheat to water logging, Australian J. Agric. Res., 54: Snape J (2001). The influence of genetics on future crop production strategies: From traits to genes, and genes to traits. Ann. Appl. Biol., 138: Soltani A, Galeshi S, Zeinali E, Latifi N (2002). Germination, seed reserve utilization and seedling growth of chickpea as affected by salinity and seed size. Seed Sci. Technol., 30(1): Willenborg CJ, Wildeman JC, Miller AK, Rossnaged BG, Shirtliffe SJ (2005). Oat Germination Characteristics Differ among Genotypes, Seed Sizes, and Osmotic Potentials. Crop Sci., 45:

Seed Size of Wheat Variety Grown in Multi-Environment

Romanian Biotechnological Letters Vol. 15, No. 6, 2010 Copyright 2010 University of Bucharest Printed in Romania. All rights reserved ORIGINAL PAPER Seed Size of Wheat Variety Grown in Multi-Environment