Molecular Mapping of the Genome and Agronomic Traits in Cowpea

Cowpea [Vigna unguiculata (L.) Walp.], 2n = 2x = 22 (620 Mb/1C), is an important food legume crop in over 65 countries, including the southern U.S. It is an excellent source of proteins, minerals and antioxidants, and a unique source of genes for many agronomic traits such as drought tolerance, heat tolerance, efficient use of soil minerals and water, low-phosphorus tolerance, disease resistance and insect resistance. However, cowpea has been subjected to limited modern genomics research. To explore its unique genes and enhance its research and breeding, we screened widely used cowpea breeding germplasm lines and developed several populations of recombined inbred lines (RILs) segregating for these and other agronomic traits. We sequenced the Golden Eye Cream (GEC) x IT98K-476-8 population consisting of 184 RILs using the high-throughput sequencing-based RAD-seq technology. Analysis of the sequences identified 4,154 high-quality SNPs, from which we constructed an RAD-seq-based SNP genetic map for cowpea. The map consists of 11 linkage groups, with 4,154 high-quality SNP markers distributing in 2,254 haplotypes and 756 chromosomal bins, and spanning a total of 837.62 cM, thus having a density of one SNP marker in approximately 0.20 cM or 149 kb. We have also phenotyped numerous agronomic traits of the population, including heat tolerance, drought tolerance, plant height, flowering date, maturity date, biomass/plant, pods/plant, pod weight/plant, seeds/pod, grain yield/plant, 100-seed weight, etc. We are currently mapping these agronomic traits using the map, thus providing toolkits to ultimately clone the genes and enable enhanced cowpea research and breeding.