Comparative analysis of heat stress indices for selection of thermo-tolerant genotypes in Indian mustard (Brassica juncea L.)

Indian mustard ( Brassica juncea L.) is a major oilseed crop in India, accounting for about 90% of the country’s Brassica oilseed area. Increasing heat stress, particularly terminal heat stress during flowering and grain filling, is a significant threat to mustard productivity. This study aimed to identify heat-tolerant mustard genotypes using yield-based stress tolerance indices. A total of 154 genotypes were evaluated under timely-sown (non-stress) and late-sown (terminal heat-stress) conditions over two Rabi seasons in an augmented block design. Grain yield data were used to compute eleven stress tolerance indices. Analysis of variance revealed significant genetic variability among genotypes for all indices. Correlation and principal component analyses identified STI, GMP, MP, HM and MRP as the most effective indices for selecting high-yielding, heat-tolerant genotypes; because these five indices are strongly inter-correlated ( r = 0.99–1.00), STI together with GMP is recommended as a parsimonious selection criterion. Cluster analysis grouped the genotypes into 13 clusters, with clusters 5 and 6 showing superior performance under stress. Genotypes RH-2049 and RH-2050 exhibited superior stability and adaptability, showing the highest values for the key productivity indices and maintaining high yields across environments, whereas Varuna, Radhika and Pusa Vijay were highly susceptible, with grain-yield reductions exceeding 40% (up to 42.4%). Overall, the study demonstrates substantial genetic variability for heat tolerance in mustard and highlights RH-2049, RH-2050 and related cluster members (RH-725, RH-2004, RH-2041, RH-1935) as potential donors for breeding climate-resilient cultivars. The findings provide a strong basis for developing climate-smart mustard breeding strategies to sustain oilseed production under rising temperatures.