The effect of drought stress on qualitative and quantitative traits of spring rapeseed (Brassica napus L.) cultivars

In order to evaluate spring rapeseed (Brassica napus L.) cultivars subjected to drought stress, the experiments were laid out as a randomized complete block design with split-plot arrangement (4 replications), during 2008-2009 and 2009-2010 cropping seasons at Seed and Plant Improvement Institute of Karaj, Iran. In this research the main factors, allotted to the main plots, consisted of two irrigation regimes including normal irrigation (I) during the total growing period based on 80 mm evaporation from class A pan and water deficit stress (S) as ceased irrigation since the flowering stage until full maturity. Subplots, which consisted of split plots, were devoted to twenty spring rapeseed cultivars. Water deficit stress, caused reduction in plant height, branch plant(-1), siliqua plant(-1), seed siliqua(-1), 1000-seed weight, seed yield, biological yield, oil content, and oil yield while it did not affect harvest index significantly. Correlation coefficient analysis revealed that number of siliquae per plant had the highest correlation with seed yield (r = 0.65, P < 0.01) as compared with other yield components. Among cultivars, 'Hyola 401' (hybrid) produced the highest seed yield (4588 kg ha(-1)) under normal irrigation, and RGS003 had the maximum seed yield (3577 kg ha(-1)) and stress tolerance index (STI = 0.952) under water deficit stress conditions. 'Quantum' with the least seed yield in both irrigation patterns (I - 3492 kg ha(-1) and S - 2948 kg ha(-1)) and low STI (0.601) had the highest susceptibility to water deficit stress. Based on the result of this study, it can be concluded that RGS003 cultivar had better capability to tolerate drought stress and could produce greater seed yield under stress conditions.