Mapping of Major QTLs Conferring Higher Branching Numbers in Backcross Introgression Lines of Sinapis alba + Brassica juncea Somatic Hybrids

Sinapis alba genome has been utilized as a donor for abiotic and biotic stress tolerance, yet there seems to be a gap in exploring its potential contribution to yield-related traits. The greater number of lateral branches in Brassica plants provides new sites for bearing siliquae and emphasizes their profound impact on yield potential. The present investigation involves the morphological characterization of 94 backcross introgression lines (BCILs) over two consecutive crop seasons, coupled with genotyping by 277 S. alba genome-specific monoallelic microsatellite markers to decipher the genetic loci contributing to higher branching number traits. The results revealed significant QTLs governing primary (PB) and secondary branching (SB). In CS-I, two QTLs linked to PB collectively explained 46.50% of the phenotypic variance (PVE), exhibiting positive additive effects, signifying their contribution to increased branch numbers in BCILs. Two QTLs associated with SB were also identified, with LODs of 5.07 and 4.21 contributing 22.55 and 17.90%, respectively, to the PVE. During the CS-II, one QTL was identified for PB, explaining 28.04% of the PVE at a 20.97 LOD value, and one major QTL for SB was identified (27.52% of the PVE). Moreover, we also identified 40 potential genes within the QTL regions, with sixteen genes homologous to the ANT, MAX2, PNH, RAX2, SEU, CRE1, and RAMOSUS1 of Arabidopsis and pea, and a total of nine unknown genes with a role in branching that were introgressed from S. alba to B. juncea. This is the first study to identify introgressed candidate genes involved in Brassica branching.