Deciphering heat stress tolerance indices for identifying terminal heat-tolerant bread wheat genotypes

High temperatures during the grain-filling period are a significant constraint in wheat production. Effective selection criteria help plant breeders utilize genetic variation more efficiently, improving stress tolerance in wheat. This study intends to investigate bread wheat genotypes' heat stress tolerance indices to identify and select heat stress-tolerant wheat genotypes. This study assessed 48 bread wheat genotypes during the wheat growing seasons 2021 and 2022 under both optimum and heat stress conditions. Twelve different stress indices were calculated, followed by correlation analysis, principal component analysis (PCA), cluster analysis and Multi-Trait Genotype-Ideotype Distance Index (MGIDI) analysis, all performed using the stress indices. Analysis of variance results showed that genotypes differed significantly for each stress index examined in the study. The significant drop in average grain yield across all genotypes under stress compared to optimal conditions indicates a considerable effect of heat stress on grain production. The results of the correlation, PCA and MGIDI analyses revealed that mean productivity (MP), geometric mean productivity (GMP), harmonic mean (HM) and mean relative performance (MRP) were key discriminating indices in explaining heat stress tolerance among 48 wheat genotypes. Principal component, cluster analysis and MGIDI results were used to draw the inference that GS/2019-20/6046, GS-2018- 19/1007, HPYT-2019-20/416, SAWYT-2018-19/309 and GS/2019-20/5042 show high yielding indices and are suitable under heat stress environment. Thus, the mentioned genotypes hold promise for cultivation in high-temperature environments or as genetic reservoirs for integrating genetic variants into wheat genotypes, enhancing their resilience to heat stress.