Investigates the Physiological and Biochemical Aspects of Rapeseed (Brassica napus L.) Cultivars under Drought Stress and Delayed Planting Date

Rapeseed is a valuable oil crop due to its high nutritious value and ample oil content. Water deficit is one of the crucial limiting factors which reduce crop growth and productivity. The present study aimed to evaluate rapeseed cultivars in the irrigation cut-off conditions in the final stage of reproductive growth (pod formation until full maturity) and planting date delay in selecting the best cultivars for recommendation in autumn rapeseed planting. This experiment was implemented in two crop years of 2015-2016 and 2016-2017 as a factorial split-plot in the form of a randomized complete block design with three replications in Karaj region, Iran. In the present study, irrigation in two levels, including well-watered irrigation and irrigation cut-off from the sowing and pod formation stages in two levels, including September 27 and October 27 as the main plot and four winter rapeseed cultivars, including Tassilo, Elvise, Neptune and Okapi were placed in subplots. The highest content of chlorophyll in both planting dates (September 27 and October 27, respectively, with values of 1.59 and 1.88 mg.g-1 Fw) and under normal irrigation conditions belonged to Elvise cultivar. Irrigation cut-off reduced relative water content of leaves and increased leaf proline, soluble protein content and soluble carbohydrate content. Elvise and Neptune cultivars had the highest seed yield under normal irrigation conditions with 3346 and 3220 kg.ha-1, respectively, and under irrigation cut-off conditions, with a mean of 3211 and 3081 kg.ha-1, respectively. According to the stress tolerance index (STI), Elvise cultivar was identified as the most tolerant cultivar under dehydration stress in pod formation stage. Elvise cultivar can be recommended as a suitable cultivar for planting in areas similar to the experimental area where moisture stress is likely to occur in the late stages of growth due to its yield indices in drought stress and non-stress conditions highest seed yield.