Seed yield and physiological responses to deal with drought stress and late sowing date for promising lines of rapeseed (Brassica napus L.)

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.