Integrating heat stress tolerance indices based on grain yield for the selection of resilient wheat genotypes

Wheat productivity is threatened by terminal heat stress, which hampers yields 6-10% per 1 °C above optimal temperatures during grain filling. Although heat stress tolerance indices offer objective selection criteria, their individual effectiveness varies with genetic background and environment. This study evaluated 230 diverse bread wheat genotypes across six environments (three locations × two seasons, 2021-23) under timely- and late-sown conditions to identify heat-tolerant germplasm using an integrated multivariate framework. Significant genotypic variation ( P < 0.001) was detected for grain yield under non-stress (Yp), heat-stress (Ys) conditions, TOL, and STI, whereas HSI showed no significant genotypic effect. Correlation analysis revealed strong positive associations among the yield-derived stress tolerance indices, reflecting their shared dependence on grain yield under contrast conditions. PCA captured 95.23% of the total variation in the first two components, with Yp, Ys, STI, and TOL defining the major productivity-related dimension and HSI contributing predominantly to a susceptibility-related dimension. Hierarchical clustering separated the genotypes into three contrasting stress-response profiles. MGIDI selected 34 genotypes at 15% selection intensity, with 28 (82.4%) belonging to the cluster showing a comparatively favorable stress-response profile. Genotypes G10037, G10018, and G12015 showed consistent identification across index-based ranking, clustering, and multi-trait selection. These genotypes represent promising candidates for further evaluation under terminal heat-stress environments. The results demonstrate that combining complementary multivariate approaches can improve prioritization of wheat germplasm while avoiding overreliance on highly correlated yield-derived stress indices.