The introduction of new genotypes of crop plants is among the most strategic research programmes, especially in arid and semi-arid regions. To study the effect of drought stress on seed yield and some physiological traits of promising lines of rapeseed at different sowing dates, an experiment was conducted for two years (2015-2017) in a semi-arid region of Iran. In this research, two conventional sowing dates were set in October 12 and November 1 (late sowing). Irrigation was carried out at two levels: normal irrigation (control) and irrigation interruption from the silique formation stage to the next stage (late-season drought stress). The genotypes included four promising lines (L1112, L1091, L1093, L1206), and a cultivar (Okapi) as a control. Results showed that delayed sowing and drought stress increased carbohydrate content and decreased seed yield, with the highest carbohydrate content and highest yield loss in L1112 and the lowest carbohydrate and lowest yield loss in the L1206 line. Among the physiological traits measured, stomatal resistance had the highest degree of correlation and the highest direct negative effect on seed yield, which declined with increasing stomatal resistance. L1112 had the highest stomatal resistance (52.76 s cm-1) in delayed sowing and drought stress conditions. Therefore, L1206 and L1112 were revealed to be resistant and sensitive lines, respectively.

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Climate change and water scarcity are among the significant limited factors to constrain the production and development of oilseed crops, especially rapeseed (Brassica napus L.), in arid and semi-arid areas. The effects of drought stress and late-sowing on the grain yield and oil quality of rapeseed were studied by conducting a factorial split-plot experiment as a randomized complete block design with three replications for two years (2015-2017) in Karaj, Iran. Irrigation and sowing date treatments were considered in the main plots as factorial, and cultivars were placed in subplots. Two sowing dates were the regular date (October 7th) and the late-sowing date (November 6th). Irrigation was also carried out at two levels of normal irrigation and irrigation interruption from the flowering stage onwards. Experimental cultivars included ES Hydromel, ES Alonso, ES Darko, ES Lauren, and Ahmadi. The highest grain yield (4505.6 kg ha-1) was obtained on the regular date, and the normal irrigation. ES Hydromel had the best quality of oil and grain meal due to the highest percentage of palmitic acid (4.44%) under late cultivation and drought stress and the lowest glucosinolates (23.19 µmol g-1 DW) content under late cultivation. Therefore, the ES Hydromel hybrid cultivar was more successful in optimal use of water resources in the face of water scarcity and late-planting in arid and semi-arid regions.