Effect of terminal heat stress on yield and yield components of bread wheat genotypes

Grain yield of wheat is severely affected by various biotic and abiotic stresses. Among the abiotic stresses, heat (terminal high temperature) is one of the major causes of low productivity in the late sown conditions in India. In the present investigation, two F2 progenies, from PBW 373 x WH 1081 and PBW 373 x PBW 343 along with their parents and four check varieties (Raj 3765, WH 730, DBW 17 and WH 711) were evaluated in field. Parents and checks were sown under normal (29 Nov., 2011) and late (3 Jan., 2012) conditions, while F2 were sown under late condition only. Data were recorded on 152 plants from each of the both crosses along with parents and check varieties for yield, yield components and physiological traits. Two factors ANOVA exhibited highly significant differences for genotypes, environments and for genotype x environment interactions for days to heading, days to anthesis, days to physiological maturity, grain filling duration, plant height, productive tillers/plant, grains/spike, 1000-grain weight, grain yield/plant, biomass/plant, harvest index and membrane thermostability (MTS). Heat susceptibility index (HSI) for 1000-grain weight and grain yield/plant was observed to be low in all tolerant genotypes (PBW 373, Raj 3765 and WH 730). The performance of heat susceptible parents was affected to more extent in late sown conditions as compared to that in tolerant parents. Grain yield/plant showed a positive correlation with plant height (0.69** and 0.28**), biomass/plant (0.98** and 0.94**) and number of productive tillers/plant (0.89** and 0.85**) in both the crosses. A wide range of variation was observed for days to heading, days to physiological maturity, grain filling duration, productive tillers/plant, grains/spike, biomass/plant, 1000-grain weight, grain yield/plant, canopy temperature depression (CTD) and MTS in first cross, while there was lesser variability in this population as compared to the previous population, for grain filling duration, 1000-grain weight, grain yield per plant, biomass, CTD and chlorophyll fluorescence. A total of 10 segregants expected to yield better performing progeny in heat stress/late sown conditions were selected from each of the two F2 populations.