Evaluation of the effects of post-anthesis heat stress and nitrogen levels on grain yield and grain growth of wheat genotypes under Khuzestan conditions

In order to study the effects of post-anthesis heat stress and nitrogen levels on grain yield and yield component of wheat genotypes، two separate field experiments were conducted in delayed and optimum sowing dates under Ahvaz conditions (2006-2007) in Islamic Azad University of Ahvaz. Plants in delayed sowing experienced heat stress from post-anthesis growth stage. Each split-polt experiment had a randomized complete block design with three replications. The application rates of N at three levels (50، 100، and 150 KgNha-1) were in main-plots. Sub-plots were consisted of six bread and durum wheat genotypes. The results indicated that the grain yield reduction in 50 and 100 KgNha-1 compared with 150 KgNha-1 treatment was 41% and 21% under optimum and 44% and 26% under heat stress conditions، respectively. In all genotypes، grain yield and 1000-grain weight (TGW) reduction under post-anthesis heat stress conditions was 42% and 33%، respectively. The highest and the lowest grain yield reduction due to heat stress were observed in Star (39%) and Vee/Nac (27%) cultivars. The Grain yield reduction in low nitrogen levels treatments and post-anthesis heat stress were due to significant reduction in number of grains. m-2 and TGW، respectively. In low nitrogen levels treatments grain number per area was reduced due to reduction in number of fertile florets/spikelets، spikes. m-2، and spikelets. spike-1. Grain growth period average were 23 and 16 days under optimum and post-anthesis heat stress conditions، respectively. Heat stress after anthesis reduced the grain growth rate (12%) and grain growth period (30%) compared with optimum conditions.