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 (<i>Brassica napus</i>). 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 (<i>mbm1</i>). Here, agronomic trait analysis showed that the <i>mbm1</i> 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 <i>mbm1</i> 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, B<i>naC03G0462000ZS</i> (<i>BnaC03.GAE6</i>) and <i>BnaC03G0491900ZS</i> (<i>BnaC03.MEE14</i>), 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 <i>mbm1</i> 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.