Evaluation of the response of Brassica species genotypes to drought and heat stresses at terminal growth stages in Gonbad area.

In order to study the effect of sowing date on different species of Brassica, an experiment was conducted at Agricultural Research Station of Gonbad during 2008– 2010 in three replications. Two genotypes of mustard (Bard-1 and J-98-102/51-5), two genotypes of turnip (Rainbow and Parkland), three genotypes of canola (Hyola401, RGS003 and Shiralee) and Select4 (a cross between canola and mustard) were genotypes of the experiment. The experiment was replicated at three sowing dates of mid November, mid December and mid January. With a delay in sowing date the number of days to physiological maturity and aboveground dry matter decreased, considerably. The number of days to physiological maturity in first, second and third sowing dates was 168, 156 and 141 days, respectively. Also Mean of aboveground dry matter at physiological maturity in first, second and third sowing dates was 11412, 10154 and 9606 kg/ha, respectively. With a delay in sowing date seed yield decreased, considerably. The mean seed yield in first, second and third sowing dates was 2362, 2227and 1939 kg/ha, respectively. Compared with mustard and turnip genotypes, seed yield of canola genotypes decreased higher, with delay in sowing date. Hyola401 hybrid had the highest seed yield and harvest index, due to higher seed number per pod and 1000-seed weight. The mean seed yield of Hyola401 hybrid in first, second and third sowing dates was 2851, 2524 and 2173 kg/ha, respectively. Also the mean harvest index of Hyola401 hybrid in first, second and third sowing dates was 24.3, 23.3 and 21.4%, respectively. In Gonbad area, occurring of terminal drought and heat stresses are current, which can decrease growth period, seed filling period, and so seed weight and seed yield. Under these conditions, sowing date is an important management tools to decrease negative impact of high temperature during flowering and seed filling periods, increasing seed number per square meter, seed weight, and seed yield.