Introgression and QTL mapping conferring resistance for Alternaria brassicae in the backcross progeny of Sinapis alba + Brassica juncea somatic hybrids.

KEY MESSAGE: A total of three QTLs, responsible for A. brassicae resistance were introgressed into S. alba - B. juncea introgression lines from S. alba and mapped through donor genome-specific SSR markers. Alternaria brassicae is a key pathogen of the Brassicaceae family causing severe blight disease to oilseed crops that leads to heavy yield losses due to lack of resistance source within cultivated Brassicas. However, the host resistance present in the Sinapis alba, an allied member of the Brassicaceae family is still unexplored precisely due to the unavailability of segregating population for Alternaria blight resistance and scarcity of donor genome-specific genetic markers. The present study was undertaken to identify quantitative trait loci governing resistance to Alternaria blight which was introgressed from S. alba to the backcross population of stable S. alba + B. juncea somatic hybrids (2n = 60; AABBSS). The second backcross population showed significant phenotypic variations for Alternaria blight ranging from immune to highly susceptible phenotype, thus suggesting quantitative nature of resistance for the disease. A subset of 154 BC2F3-4 lines was used for disease screening and genotyping with 234 S. alba genome-specific microsatellite markers. As a result of the study, twelve linkage groups were developed corresponding to 12 chromosomes of S. alba (n = 12) covering a length of 1694.02 cM. The chromosomes 5 and 11 harbored a total of 1 (Abr-01), and 2 (Abr-02, and Abr-03) QTLs detected by ICIM-ADD mapping method at LOD score values 3.7, 5.12, and 6.74, respectively. The QTLs identified during the study have a range of 5.51-10.87 percent phenotypic variations for disease resistance. To the best of our knowledge, this is the first report of QTLs introgression for A. brassicae resistance in cultivated Brassica from an allied member of Brassicaceae.