Genetic Mapping and Identification of Candidate Genes for a New Multi-Branching Mutant mbm1 in Brassica napus

Branch number is an important agronomic trait that determines the number of siliques per plant and yield in rapeseed (Brassica napus). However, the complex genetic and molecular mechanisms regulating the formation of branch number in rapeseed remain unclear. In a previous study, we isolated an EMS-induced multi-branching mutant (mbm1). Here, agronomic trait analysis showed that the mbm1 mutant produced more effective primary branches, total silique number, and yield per plant compared with the wild type. Genetic analysis indicated that the multi-branching trait of the mbm1 mutant is controlled by incompletely dominant gene(s) and follows nuclear inheritance. As a result of combined BSA-seq-based mapping and RNA-seq profiling, two candidate genes, BnaC03G0462000ZS (BnaC03.GAE6) and BnaC03G0491900ZS (BnaC03.MEE14), were identified based on sequence variation and expression differences. KASP marker analysis confirmed that there are significant associations between these two gene loci and the multi-branching trait. Hybrid progeny derived from crosses between the mbm1 mutant and commercial cultivars L329 and ZS11 showed significantly improved yield due to increased effective branch number. Together, these results provide important genetic resources and a theoretical foundation for further elucidating the genetic regulatory network of branching in rapeseed and for developing high-yielding rapeseed varieties with ideal plant architecture.