Marker-assisted introgression of large seed size QTLs into a cowpea cultivar from Senegal

Cowpea (Vigna unguiculata), also known as black-eyed pea, is a warm season legume cultivated extensively in West and Central Africa. Cowpea is one of the highest sources of protein, folic acid and several vitamins for many people in sub-Saharan Africa. Incorporating information on consumer preferences is important for decisions on developing improved cowpea cultivars, and increased seed size is one of the targeted preferred traits. In order to develop new cowpea cultivars with large seed, genetic markers (SNPs) are being employed to introgress two QTLs (Css-1 and Css-4) for large seed size from the recombinant inbred line “113-4-6-14-1” (CB27/IT82E-18 x CB27) into “Pakau,” a new popular cultivar in Senegal. Recently, a 60k assay genotyping platform has been developed for cowpea and used for genotyping the CB27 x IT82E-18 population, in which Css-1 and Css-4 were mapped previously (Lucas et al. 2013, Front Plant Sci.). A total of 16566 high quality SNPs segregated in this population, and were used in QTL mapping to identify new SNPs within the seed-size QTL regions. These SNPs will be used for marker-assisted backcrossing to incorporate Css-1 and Css-4 into Pakau. Four possible combinations will be analyzed to test the effect on seed phenotype of these QTLs in the Pakau genetic background: no QTL, each of the two QTLs, and both QTLs. Future studies will include determining the effect of increasing seed size on both yield and the nutritional quality of cowpea.