Effects of post-anthesis heat stress and nitrogen levels on grain yield in wheat (T. durum and T. aestivum) genotypes

      In order to study the effects of post-anthesis heat stress and nitrogen levels on grain yield and yield components of wheat genotypes, two separate field experiments were conducted in delayed and optimum sowing dates under Ahvaz conditions (2006-2007). The Ahvaz site located in south west of Iran (32°20' N, 40°20' E) with subtropical climate condition. The experiment site had a moderate winter and dry and hot summer. Plants in delayed sowing date experienced heat stress at post-an thesis 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 assigned 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 treatments 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 33% and 42%, respectively. The highest and the lowest grain yield reduction due to heat stress were observed in Star (39%) and Vee/Nac (27%) genotypes. The Grain yield reduction in nitrogen deficiency treatments and post-anthesis heat stress was due to significant reduction in number of grains. m-2 and TGW, respectively. In nitrogen deficiency treatments grain number per area was reduced due to reduction in number of fertile florets. Spikelets-1, spikes. m-2, and spikelets. spike-1. Further research are recommended for full understanding the effects of heat stress and low N level on yield and yield components of recommended wheat genotypes under agroclimatic conditions such as south west of Iran.