Genome wide association studies for yield and its component traits under terminal heat stress in Indian mustard (Brassicajuncea L.)

Breeding for terminal heat stress (THS) in Brassica juncea L. Czern & Coss is recognized as an imperative objective for sustained productivity in contemporary climatic changes. A fixed diversity stock of 491 genotypes was documented for wide range of variations for seed yield under natural terminal heat stress. A set of top 20 genotypes comprising introgression lines from wild species Erucastrum cardaminoides and B. tournefortii; derived B. juncea lines using B. carinata and B. napus; land races;, commercial cultivars and breeding lines, having the lowest heat susceptibility index and the least yield reduction under heat stress, have been identified as potential heat tolerant donors. A panel of 96 genotypes was constituted from this stock on the basis of their differential response to heat susceptibility index and seed yield reduction under natural THS. The constituted panel was evaluated for validation under controlled conditions for ten seed yield-related traits. Moderate to low correlations between SY and its related traits were observed in NS and THS conditions. Double digest restriction site associated DNA sequencing of 71 genotypes identified 18,258 SNPs after filtration. Least square means of all the traits under NS and THS conditions and the best linear unbiased predictors along with identified SNPs were used for genome-wide association study. A total of 34 SNPs under NS, 24SNPs under THS and 30SNPs using BLUP values were found to be associated with all seed yield-related traits. Chromosome B05 harbored the maximum number of SNPs (nine) followed by chromosomes A07 and A09 (eight SNPs each). SNPs under NS conditions could not be associated with THS. This is the first report on the identification of 24 marker-traits associations detected for SY and its component traits under THS conditions. It may be possible to develop the molecular markers for significant SNPs after due validation. The constituted panel may also serve as a source of allelic diversity for genes controlling various economic traits. The derived introgression lines as potential heat tolerant donors indicated the possibility of using wild species to breed for abiotic stress tolerance in Indian mustard.