A Study of the Effect of Terminal Heat Stress on Source Restriction and Grain Yield in Bread Wheat (Triticum aestivum L.) Genotypes under Khuzestan Conditions

In order to study the effects of post – anthesis heat stress on source of six wheat genotypes (Vee/Nac, Chamran, S79-10, Dez, Fong and Kaveer), two separate field experiments were conducted as delayed as against optimum sowing dates in Ahvaz coditions. Plants in delayed sowing date experienced heat stress at post-anthesis growth stage. As study of grain yield indicated that the highest and the lowest grain yields in optimum conditions belonged to Chamran and Fong genotypes, respectively. The highest and the lowest grain yields in stress conditions were obtained for Vee/Nac and S79-10 genotypes, respectively. The highest and the lowest stress susceptibility index (SSI) for grain yield and also the highest and the lowest reduction in grain yields occurred for S79-10 and Fong genotypes, respectively. Chamran and Kaveer genotypes expressed the highest and the lowest stress tolerance indexes (STI) for grain yield. Mean of source restriction in optimum and heat stress conditions were 8.3% and 24%. Mean of source restriction aggravation in late heat stress was 29%. Higher source limitation in a late maturity genotype such as S79-10 was related to delay in anthesis and a coincidence of grain growth period with heat stress. In such short-season genotypes as Fong and Vee/Nac with early anthesis, grain growth period was ahead of heat domineering conditions. Indeed the lowest source restriction along with the lowest grain yield reduction were recorded in these latest mentioned genotypes.