Current status of molecular tools development for cowpea [Vigna unguiculata (L.) Walp.] improvement

Cowpea [ Vigna unguiculata (L.) Walp.] is a popular tropical grain legume which is widely produced and consumed in sub-Saharan Africa (SSA). The grains are rich in dietary protein for human while the haulm is high quality fodder for livestock particularly ruminants. Compared with many other crops cowpea is a laggard in development, evaluation and deployment of different molecular markers for use in genetics and breeding. Application of DNA-based markers is of considerable significance to crop improvement. Some DNA based markers have been used to study genetic diversity, linkage and quantitative traits loci (QTL) mapping in cowpea. Results from these studies have demonstrated the extent of genetic diversity in cowpea and its relationship with other members of the Vigna species. In addition, genetic linkage maps have been produced and used for detection of QTLs for some desirable traits. Some of these include QTLs for seed size, seed coat and eye color, leaf shape, pod length, resistance to macrophomina, domestication-related traits such as pod length, days to flowering, etc. In view of the potential benefits of DNA markers to the development of better performing improved cowpea varieties, concerted efforts are now being devoted to develop molecular tools for the crop. The developed consensus genetic linkage map and genome sequence for cowpea will boost the application of molecular tools for its genetic improvement. A panel of 17 SNP markers have been developed for use in quality assurance and control in cowpea breeding activities. This review aims at highlighting the molecular approaches that have been used and being pursued for genetic diversity, QTL mapping of some qualitative and quantitative traits as well as marker-assisted selection leading to the development of high performing new improved lines that meet the needs of farmers and consumers.