ANTIOXIDANT ENZYME ACTIVITIES AND GRAIN YIELD OF RAPESEED (Brassica napus L.) OF RESPONSE TO LATE-SEASON DROUGHT AND SOWING DATE

Drought stress and oxidative damage are among the most important factors that limit the growth and yield of drought crop plants. The global climate change has led us to adapting planting dates and select tolerant cultivars to encounter the new climatic conditions. To evaluate the effect of late-season drought stress under different planting dates on rapeseed cultivars, a 2- year field experiment was conducted as a factorial split-plot based on randomized complete block design (RCBD) in Karaj - Iran, from 2015 to 2017. Irrigation treatments were considered in the main plots and planting dates and cultivars as factorial were placed in subplots. Two planting dates were regular date (September, 26) (PD1) and late planting date (October, 26) (PD2). Irrigation was also carried out at two levels of normal irrigation (NI) and irrigation cut-off (II) from the pod formation stage onwards. Rapeseed cultivars included Tassilo, Elvise, Neptune and Okapi. Late-season drought stress and delayed planting date reduced anthocyanin (AN), guaiacol peroxidase (GPX) activity, and grain yield (GY), but increased malondialdehyde (MAD), in all rapeseed cultivars. The highest GY (3346.6 kg ha(-1)) was obtained in NI conditions and PD1. According to the results of stepwise regression, AN, GPX, and MAD with a coefficient of determination (R-2 =0.774) explained about 78% of the changes in the GY, among which MAD with a value of (-0.72) showed the greatest negative and significant impact on the GY. Therefore, Elvise can be introduced as a superior cultivar to be selected as a genotype that presents acceptable resistance under drought stress and late sowing in arid and semi-arid regions.