Effect of high temperature stress at post anthesis stage on photo system II, senescence, yield and yield attributes of wheat genotypes

Wheat [Triticum aestivum (L.) emend Fiori and Paol.], a major cereal of north India experiences high temperature during anthesis and grain development stages coupled with sharp irradiance, low humidity and moisture deficit, resulting in adverse effect on different vital activities and finally the yield and yield attributes of the crop. Wheat genotypes may have variable response to these stresses, so a field experiment was conducted, where six wheat cultivars (UP-2338, PBW-343, UP-2113, PBW-175, VL¬616 and VL-421) were subjected to variable temperature conditions by sowing them timely and delayed by 20 days. Results revealed that delayed sowing negatively affected growth attributes viz. plant height and leaf area as compare to timely sown crops. The photosynthetic pigments (chI a+b) along with chI at b ratio also recorded reduction under delayed sowing as compared to timely sown cultivars. Chlorophyll fluorescence variable yield (FvIFm), which indicates the functionality of PSII also got impaired under delayed sowing. The higher temperature under delayed sowing enhanced plant growth and hastened both flowering and maturity, resulting in marked reduction in number of days to booting, heading, anthesis and maturity of wheat. Significant interaction was recorded between the genotypes and time of sowing. The yield and yield attributes in terms of spike length plant-' 1000-grain weight, harvest index and finally seed yield ha-1 recorded marked reduction under delayed sowing. UP-2338 recorded the highest grain yield both under timely and late sown conditions closely followed by VL-616. Percent reduction in grain yield due to delayed sowing was lowest in UP-2113 and the highest in VL-421. In case of test weight, PBW-343 and VL-616 maintained its significant superiority. In overall, among all the genotypes, UP-2338 was found to be best performer, while VL-421 was the worst in coping with high temperature stress.