Physiological Response of Wheat Genotypes to Post Anthesis Hyperthermal Stress

Physiological response to hyperthermal stress during grain filling stage was studied in a set of 25 diverse bread wheat varieties evaluated in four environments. In each of the two crop seasons, the mid-November sown experiment was taken as non-stress environment whereas the mid-December sown as thermal stress environment. Highly significant differences among environmental means for all the traits except photosynthetically active radiation interception (PARI) revealed the successful creation of thermal stress environment as well as the sensitivity of grain yield, its component traits and various physiological traits to thermal stress. Genotypes differed highly significantly for all the traits studied and also interacted either with crop season or with thermal regime or with both. In thermal stress environment, K 2008, PBW 498 and 9HTWYT-21 had low membrane injury (Ml) and WH 736 recorded more PARI. Most sensitive trait to thermal stress was biological yield (reduction 31.50%) followed by grain yield (29.94%), Ml (−15.19%) and days to maturity (13.54%) whereas PARI and harvest index were least affected by thermal stress. Heat susceptibility index for each genotype with respect to various traits was calculated.