During the formation of callus besides of genotypic factors, the effects of nutritional supplements of the culture media are well known (Mathias and Simpson 1986; Kato et al. 1991). Also, correlation between seed size and several physiological events such as germination of the seed and development of the plantlet are also known to be significantly important (Kalakanavar et al. 1989; Ries and Everson 1973). Since in the endosperm-supported mature embryo culture method, nutritive materials of the endosperm are used during the formation of the calli, the amount of these materials with respect to seed size becomes another significant factor. Therefore, as shown in Table 1, for the cultured embryos of two different seed sizes for each genotype, while the response of callus induction of large seed changes between 90% to 100%, this value was observed to be between 76.6% to 88.3% for small size seeds. In the species, the variation of the callus induction ability with respect to seed size was also found to be statistically significant.

Such significant difference between calli fresh weight and seed size was also observed when compared both interspecifically and intraspecifically. ally. In contrast, while genotypically higher 1000-kernel weight containing hexaploid (T. aestivum, 48.2 + or - 0.33g) and tetraploid (T. durum, 58.2 + or - 0.86g) wheats reached to highest average callus fresh weight (1462.0g and 1442.3g, respectively) at their large seed group, smaller 1000-kernel weight containing diploid wheats (T. boeoticum, 24.5 + or - 0.39g and T. monococcum, 23.8 + or - 0.49g) reached to much lower average callus fresh weight (1170.7g and 1051.0g, respectively) at their large seed group. When each species was examined within itself, mean weight of callus of large seed group was also found to be significantly higher than the small seed group. Seed size was observed to have obviously significant effect (P<0.05) on the weight of callus, especially when the results from the large seeds both genotypically and specially selected ones among the species, were compared with the small seeds.

As stated by Vasil (1987), embryonic calli with high regeneration capacity consist of low intercellular space containing compact tissue. Thus, such tissues of calli are expected to be heavier and as a consequence, callus fresh weight may be used as a good indicator of regeneration capacity. Besides, when the regeneration capacity of calli for each species were examined, calli with higher weight from large seeds had also higher regeneration capacity (P<0.01) than calli with lower weight from small seeds. This has also reflected on the culture efficiency of large seeds, which changed between 88.3%-93.3% whereas in small seeds of each species such change occurred with significant decrease (P<0.01) between 60%-65% (Table 1).

In conclusion, the results suggested that seed size have profound effect not only on the calli formation, but also on the fresh weight dependent increase in the regeneration capacity of those calli. It was also possible to support these results when the correlation values between seed size and total callus weight (r=0.86**) as well as between total callus weight and regenerative callus amount (r=0.85**) were examined. Significant positive correlation between callus induction and number of plants regenerated have been reported previously (Ozgen et al. 1996). Finally, it is possible to conciliate that when the endosperm-supported mature embryo culture method is applied on genotypes with selectively larger seed size, callus induction and its regeneration can be increased significantly and mature embryos can be used as an effective explant source in wheat tissue culture.

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