محمد مدرسی

There are areas across the world where the temperature in the spring months rises and crops are exposed to late season heat stress, especially during the critical period of grain filling. In south western parts of Iran, including Bushehr and south part of Khuzestan Provinces, wheat grain filling period is shortened due to high temperature stress at the final stages of growth cycle. In these regions, late sowing is responsible for a significant wheat yield loss compared with cooler regions, as temperatures often exceed 30 °C during the grain filling period. Late season heat stress, often occurring during booting, heading, anthesis and grain filling stages is considered as one of the major environmental limiting factors that drastically reduces grain number per spike, grain weight and final grain yield throughout most of the bread wheat growing areas in warm and dry regions of Iran. Post-anthesis heat stress in wheat induces several physiological effects which eventually result in smaller grains due to shortened grain filling period or/and reduced grain filling rate. In addition, early sowing dates are limited due to hot days at the beginning of autumn. So, farmers have to wait until late autumn to find an optimum sowing date to do their cultivation. The adverse effect of temperature can be minimized by sowing a wheat crop within the optimum period or to breed heat-tolerant genotypes that could be sown late and very early to ensure high grain yield. Despite the abundance of research on the effect of late season heat stress on wheat across the world; studies that explore this effect on yield and heat tolerance of spring bread wheat cultivars in Bushehr, remain scant. In an attempt to contribute to this research, a laboratory and a two - year field experiment were conducted to assess and manage heat stress in wheat (Triticum aestivum.L) cultivars under Dashtestan climatic condition. The laboratory experiment was conducted to study germination and seedling growth of six