Physiological response of early and late maturity oilseed rape cultivars to drought under two climate conditions

Two experiments were performed in 2011-2012 to investigate the response of three oilseed rape cultivars to drought stress, grown under two climate conditions in Iran (cold and hot climates). The experiments were conducted using a randomized complete-block design arranged in split-plot with three replicates. The irrigation treatments (FI: full irrigation; WIF: withholding irrigation at flowering stage, and WIS: withholding irrigation at the silique formation stage until physiological maturity) were allocated to main plots, whereas subplots consisted of the oilseed rape cultivars: early maturating (GKH2005), relatively late maturing (Opera) and late maturing (Okapi). Drought caused a significant reduction in seed number, 1000-seed weight, seed and oil yield, harvest index, relative water content (RWC) and leaf stomatal conductance. Oilseed rape cultivars responded to irrigation treatments in different ways. The maximum seed number per silique in the main stem was observed in Okapi cultivar under WIS, whereas GKH2005 cultivar produced the minimum seed number per silique in the main stem in WIF conditions. There were no significant differences among oilseed rape cultivars in terms of seed yield when grown under full irrigation condition; however, under drought stress conditions, the maximum and minimum seed yields were obtained from GKH2005 and Okapi cultivars, respectively. In general, results suggest that stomatal conductance, RWC and silique number per secondary branches were the most important traits contributing to drought tolerance.