Ram AvtarChoudhary, Raju Ram2024-04-022024-04-022023-02-03https://krishikosh.egranth.ac.in/handle/1/5810208028Indian mustard is one of the most important oilseed crops and contributes more than 30% to the Indian vegetable oil pool. Heat stress is one of the major yield-limiting factors under changing climate conditions. Its impact is most severe at the reproductive stage, resulting in low seed yield. Therefore, assessment of genetic diversity, population structure, and molecular marker-traits associated with terminal heat stress tolerance in Indian mustard germplasm is necessary to accelerate the breeding effort. In the present study, a set of advanced breeding lines and genetic stocks representing 154 genotypes of Indian mustard were phenotyped for various morpho-physiological traits under control and terminal heat stress conditions. Besides, these genotypes were genotyped using 237 SSR markers. The results of the present study revealed significant effects of year, sowing date, and genotypes on various morpho-physiological traits under investigation. For the majority of the traits studied, high heritability and genetic advance were estimated. Trait association results revealed that seed yield/plant was significantly and positively correlated with plant height, number of primary branches/plant, number of secondary branches/plant, main shoot length, number of siliquae on the main shoot, siliqua length, number of seeds/siliqua, 1000-seed weight, photosynthetic rate, stomatal conductance, total chlorophyll content, and carotenoid content. DNA was isolated from all 154 genotypes by the standard method and subjected to SSR marker analysis. Out of total of 237 SSR markers, 111 were polymorphic. PIC values for all polymorphic SSR markers ranged from 0.013 to 0.627, with an average PIC value of 0.31. Unweighted Neighbor Joining-based dendrogram and population structure analysis divided the 154 genotypes into three clusters and two sub-populations, respectively. A total of 29 SSRs under timely sown and 33 SSRs under late sown environment were found to be associated with morphological and physiological traits by the MLM (Q + K) method. Chromosome B06 harbored the maximum number of SSRs (12), followed by chromosomes A08 (11) and A07 (five SSRs). Under terminal heat conditions, a total of 20 SSRs were specifically detected that were not associated under normal sown conditions. This meant that these particular genomic regions and QTLs were linked under extreme heat conditions. Overall, the heat-tolerant genotypes identified in this study and the SSR markers associated with terminal heat stress tolerance attributes will be helpful for the development of a heat-tolerant cultivar of Indian mustard through marker-assisted selection.EnglishThesis