Evaluation of source restriction intensifying of wheat spring wheat (Triticumaestivum L.) genotypes under post-anthesis heat stress

In order to study the effects of heat stress after anthesis on source limitation of six wheat genotypes, two separate field experiments were conducted in delayed and optimum sowing dates. Plants in delayed sowing date experienced heat stress in after anthesis growth stage. 50% spikelet removal was used for calculating source limitation. Study of stress indexes indicated that the highest and the lowest stress susceptibility index (SSI) for grain yield and also the highest and the lowest reduction in grain yield was in S79–10 and Fong genotypes, respectively. The highest and the lowest stress tolerance index (STI) for grain yield was found in Chamran and Kaveer genotypes, respectively. In all genotypes, mean of source limitation in optimum and heat stress conditions was 8.3% and 24%, respectively. Higher source limitation in late maturity genotypes such as S79–10 was related to delay in anthesis and contact of grain growth period with heat stress. In early mature genotypes such as Fong and Vee/Nac with early anthesis, grain growth period was before heat conditions. Indeed source limitation and also grain yield and weight reduction was the lowest in these genotypes.