Genome assembly of a Mesoamerica-derived Phaseolus lunatus cultivar enables the identification and comparative genomic analysis of a complex resistance locus

Abstract

Lima bean, Phaseolus lunatus, is closely related to common bean and is high in fiber and protein, with a low glycemic index. Lima bean is widely grown in the state of Delaware, where late summer and early fall weather are conducive to pod production. The same weather conditions also promote diseases such as pod rot and downy mildew, the latter of which has caused previous epidemics. A better understanding of the genes underlying resistance to this and other pathogens is needed to keep this industry thriving in the region. Our current study sought to sequence, assemble and annotate a commercially available cultivar called Bridgeton, which could then serve as a reference genome, a basis of comparison to other Phaseolus taxa and a resource for identification of potential resistance genes. Combined efforts of sequencing, linkage and comparative mapping analysis resulted in a 625 Mb genome assembly, as well as a better understanding of a locus underlying resistance to the current downy mildew race in the field.