Dissection of Physiological Traits for Terminal Heat Stress Tolerance in Indian Mustard (Brassica juncea L.) Using Microsatellite Markers

Heat stress, especially during the reproductive stage, has been exacerbated by changing climatic conditions, resulting in reduced seed yield in crops like Indian mustard. In the present study, 154 genotypes of Indian mustard were used to find novel SSR marker-based associations for seed yield and physiological traits by linkage disequilibrium. Extensive phenotyping of 154 genotypes for seed yield and various physiological traits was done for two consecutive years (2020-2021 and 2021-2022) in timely and late-sown environments. Out of 237 SSR markers, a total of 111 polymorphic markers containing 312 alleles were used for analysis. Two different models, i.e., general linear model (GLM) and mixed linear model (MLM), were used to detect the significant marker-trait associations for timely and late-sown environment separately. A total of 12 and 10 MTAs were found to be associated under timely and late-sown conditions with seed yield and physiological traits using MLM model. Out of these promising MTAs identified in the present study, five SSRs were specifically detected only in late-sown environments which meant that these specific genomic regions and QTLs were associated under terminal heat conditions. This is the first report on the identification of marker-trait associations for physiological traits under terminal heat stress conditions. It may be possible to develop the molecular markers for significant SSRs after due validation. The findings contribute to our understanding of the genetic basis of heat tolerance and provide valuable information for breeding programs aiming to improve crop productivity under heat stress conditions.