Selection indices for enhanced selection efficiency in Indian mustard under terminal heat stress conditions

With global increase in temperature, terminal heat stress (THS) has emerged as a major challenge in food crops. Indian mustard (Brassica juncea L. Czern and Coss), C3 plant, grows well at 15-20°C. Heat stress at seedling as well as at flowering stage leads to enhanced vegetative growth and flower abortion leading to loss in seed yield. Late sowing after cotton and rice harvest expose the crop to high temperature stress during reproductive stage of development. A fixed diversity stock of 486 Indian mustard lines were evaluated under delayed planting conditions to expose the crop to THS for two consecutive years. Selection indices were computed using four different combinations of traits via Kang_SAS Path computer program along with expected genetic advance (GA) at 5% selection intensity. Set1, comprised of five traits viz., plant height (PH), number of secondary branches (NSB), number of siliquae on main shoot (NSMS), seed yield (SY) and 1000-seed weight (TSW) were recorded the highest GA (8.612) in comparison to other trait combinations tested in present study. Other important finding was slight difference in GA of set I (8.612; SY included) and set II (8.599; SY excluded) with efficiency of selection index 131% and 130%, respectively. This recommended that in initial breeding generations (F2/F3), a breeder may base his selection on four yield related traits (PH, NSB, NSMS and TSW) only without significant loss in genetic gains. This will save resources and time of breeders to compute seed yield. This is the first report on computation of selection index for efficient simultaneous selection under THS in Indian mustard.