QTL mapping for bruchid resistance in an adzuki bean distant hybridization population using rice bean genetic resources

Bruchid beetles (<italic>Callosobruchus</italic> spp.) are major storage pests of adzuki bean (<italic>Vigna angularis</italic>) and other food legumes. While cultivated adzuki bean lacks bruchid-resistant germplasm, its close relative, rice bean (<italic>Vigna umbellata</italic>), exhibits strong resistance. This study aimed to explore bruchid resistance genes from rice bean by developing a distant hybridization population with adzuki bean, thereby providing a theoretical basis for molecular breeding of bruchid-resistant adzuki bean varieties. An interspecific hybrid population was generated using the bruchid-resistant rice bean accession F021 as the maternal parent and the bruchid-susceptible adzuki bean cultivar Baihong 2 as the paternal parent. F₁ hybrids were obtained through embryo rescue, and a recombinant inbred line (RIL) population of 178 F₈ lines was established via single-seed descent. A genetic linkage map was constructed using 3095 SSR markers to identify polymorphic loci between the parents. Bruchid resistance was evaluated over two consecutive years through artificial infestation with <italic>Callosobruchus chinensis</italic> (adzuki bean weevil), using seed damage rate (%) as the phenotypic indicator. Quantitative trait loci (QTLs) for bruchid resistance were identified by interval mapping, and their genetic effects were analyzed. The seed damage rate of Baihong 2 was consistently 100% across both years, confirming its susceptibility, while F021 displayed resistance with seed damage rates of 19.2% and 23.4%, respectively. The RIL population exhibited a continuous distribution of seed damage rates, consistent with the inheritance pattern of a quantitative trait. A total of 503 polymorphic SSR markers were identified, with the highest polymorphism rate (33.7%) observed among adzuki bean-derived markers. The final genetic linkage map included 262 markers distributed across 11 linkage groups, spanning a total length of 634.90 cM with an average inter-marker distance of 3.43 cM. Comparative genomic analysis showed good collinearity with the adzuki bean reference genome. Joint analysis of phenotypic data from both years identified nine QTLs associated with resistance to <italic>C. chinensis</italic>, including three stable QTLs (<italic>QUmbr2.1/2.2</italic>, <italic>QUmbr4.1/4.2</italic>, and <italic>QUmbr11.1/11.2</italic>), with LOD scores ranging from 2.93 to 6.56 and phenotypic variance explained ranging from 8.3% to 17.0%. All QTLs exhibited negative additive effects, indicating that alleles from rice bean significantly reduced seed damage rates. This study successfully mapped QTLs for adzuki bean weevil resistance using a distant hybridization population and confirmed rice bean as a valuable gene donor for improving bruchid resistance in adzuki bean, providing essential marker resources for molecular marker-assisted selection in breeding programs.