Evaluation of the Dry Matter Remobilization to Seeds in Winter Rapeseed Cultivars under Drought Stress Conditions

In order to evaluate dry matter remobilization to seeds in the winter type rapeseed cultivars grown under drought stress conditions, an experiment was carried out using a randomized complete block design arranged in a split plot with three replicates in Shahre-Qods, Iran, in the 2011-2012 growing season. Irrigation treatments including control (irrigation after 80 mm evaporation from evaporation pan class A) and drought stress (irrigation withholding starting from stem elongation, flowering and silique formation stages) were allocated to the main plots and three winter type rapeseed cultivars (GKH2005, Opera and SLM046) were considered as the subplots. The results showed that drought stress increased dry matter remobilization and remobilization efficiency. By contrast, agronomic traits such as the number of siliques on the main stem and secondary branches, number of seeds per silique, 1000 seed weight, oil yield, harvest index and productivity effort (silique dry weight/biomass ratio) were decreased. The GKH2005 cultivar showed the maximum seed yield, which was 1058, 1409 and 2099 kg ha-1, when irrigation withholding started from stem elongation, flowering stage, and silique formation stages, respectively; this  was due to the higher amount of remobilization and the efficiency of remobilization and maximum number of silique in  the secondary branches. In general, the results suggest that higher remobilization and remobilization efficiency are among the most important drought stress tolerance mechanisms in the oilseed rape.