Validation and fine mapping of qVmunBr6.2 locus reveal a gene encoding hevamine-A, a defense protein with chitinase activity, is associated with bruchid (Callosobruchus maculatus) resistance in black gram (Vigna mungo)

Callosobruchus maculatus (cowpea weevil) is an insect pest that causes significant yield loss in cultivated black gram (Vigna mungo var. mungo) during storage. A previous study showed that seed resistance to C. maculatus in wild black gram (V. mungo var. silvestris) accession 'TC2210' is controlled by two linked QTLs, qVmunBr6.1 and qVmunBr6.2. However, none of these QTL have been validated, and the molecular basis of these QTLs is not yet known. The objectives of this study are to validate qVmunBr6.2 and identify candidate gene(s) for bruchid resistance at this locus using wild black gram accession 'TVNu1076' as the source of resistance. QTL mapping using an F₂ population of the cross 'Chai Nat 80' (cultivated black gram) × TVNu1076 showed that qVmunBr6.2 controls the resistance in TVNu1076. Fine mapping using a large F_2:3 population of 1,144 plants located the qVmunBr6.2 to the marker interval VmBru-SSR74 and VmBru-SSR98. The markers VmBru-SSR74 and VmBru-SSR98 corresponded to a genome region of 9.27 Kb containing two genes including VmunHev encoding hevamine-A, a known enzyme involved biotic stress resistance. Compared with the wild black gram TVNu1076, sequence alignment of VmunHev revealed two one-base pair substitutions that cause amino acid changes in hevamine-A in the cultivated black grams. Gene expression analysis revealed that VmunHev expressed in the seeds. These results showed that VmunHev is a strong candidate gene conferring seed resistance to C. maculatus in wild black gram. The results present in this study provide insight into the genetic basis of C. maculatus resistance in wild black gram.