Using Genomic Resources to Breed Cowpeas With Larger Seeds

Cowpea (Vigna unguiculata) is a warm-season legume that is primarily cultivated for protein rich grain. Seed size is an important breeding target that distinguishes most domesticated crops from their wild relatives and is a particularly important trait for the grain legumes. This dissertation describes efforts to breed cowpea varieties with larger seeds using marker-assisted approaches to breeding. The first chapter of this dissertation describes the development of a consensus genetic map of 1,107 molecular markers which was constructed by analyzing bead-assay genotype data from 13 experimental populations. The content and organization of the cowpea genome was also compared to the genome of soybean (Glycine max) to describe regions of synteny. The second chapter utilizes the genetic map, legume synteny, and phenotypic information collected from field and greenhouse trials to develop associations between allelic variation and the inheritance of seed size. Many of the regions of the cowpea genome important for seed size were found to be syntenic with regions of the soybean genome that were previously associated with the inheritance of seed size. These marker-trait associations are applied in the third chapter to breed cowpea varieties with up to 52% larger seeds which was accomplished by introgressing a rare Mozambican haplotype into the genetic background of a California blackeyed pea. Preliminary field screening identified introgression lines that also performed well for other important agronomic traits including yield, maturity, and plant architecture. The introgression lines developed in this work could be used as parents for deploying large seed size in other pedigrees and could be studied to better understand the impact of seed size on nutritional content and agronomic performance.