Evaluation of indigenous and exotic wheat genotypes for tolerance to severe terminal heat stress in the agro-climatic conditions of Bihar

Terminal heat stress is a major constraint limiting wheat productivity in tropical and subtropical regions. This study aimed to assess genetic diversity and identify key traits and genotypes associated with terminal heat stress tolerance using multivariate and stress-index-based approaches. A diverse panel of 500 wheat genotypes, comprising 119 indigenous and 381 exotic entries, were evaluated under three field sowing conditions (timely, late, and very late) to impose natural terminal heat stress. Data were recorded for important phenological, physiological, and yield-related traits. Principal component analysis effectively differentiated genotypes along a tolerance–susceptibility gradient under very late sown conditions. Very late sowing (VLS) imposed severe terminal heat stress, resulting in a grain yield reduction of 58.33% and 59.41% during 2022–23 and 2023–24, respectively, with an average reduction of 58.89% compared with timely sowing. Based on their ability to maintain grain yield under terminal heat stress, as reflected by low Stress susceptibility index (SSI) and Tolerance index (TOL) values and high mean productivity (MP), Stress tolerance index (STI), Grain mean productivity (GMP), Yield index (YI), and Yield stability index (YSI) values, 22 superior genotypes (13 indigenous and 9 exotic) were identified. These genotypes were further classified based on SSI. The heat-tolerant group included genotypes such as 21HTWYT-31, 40SAWSN-3160, DBW-173, PHSL-10, NEST-20-30, 40SAWSN-3080, MP-1323, NEST-20-39, and HD-2967 © . The identified genotypes and associated traits constitute valuable genetic resources for breeding wheat cultivars with enhanced terminal heat tolerance.