Effect of heat stress due to sowing date on grain yield of rapeseed cultivars in north Khuzestan conditions in Iran

To study the effects of heat stress due to changing sowing date on grain yield of rapeseed cultivars, an experiment was carried out in Safiabad Agricultural Research Center, Dezful, Iran, in2010 11 and 2011-12 as split plot arrangement in randomized complete block design with three replications. Main plots were consisted of three sowing dates (1st November, 16th November and 1st December) and sub-plots included 7 canola cultivars (Hyola60, Hyola308, Hyola330, Hyola401, Hyola420, RGS003 and Option500). Combined analysis showed that sowing date×cultivar interaction effect was significant on flowering duration, growth duration, number of branch plant-1, number of silique.plant-1, grain yield and biological yield. The interaction effects of year×sowing date and year×cultivar were significant on oil content. The highest silique.plant-1(219.51) belonged to Hyola420 in the 1st sowing date. The lowest silique.plant-1 (124.34) belonged to the last sowing date (1st Dec) in Hyola330. The highest grain yield (4316 kg.ha-1) obtained in 1st sowing date (1st Nov) for Hyol 420 and the lowest grain yield (2022 kg.ha-1) belonged to the last sowing date (1st Dec) for Option500 cultivar. It is concluded that sowing date in early November and Hyola420 would be suitable for producing optimum grain yield and avoiding heat stress.