Evidence for two domestication events of hyacinth bean (Lablab purpureus (L.) Sweet): a comparative analysis of population genetic data

Studying molecular genetic relationships can substantially contribute to the understanding of the pathways of domestication of a species. Although an increasing number of molecular genetic studies have been performed on Lablab purpureus (hyacinth bean), many covered germplasm of restricted geographic origin or limited intra-specific systematic position. Integrating the molecular diversity found with phenotypic or morpho-agronomic diversity is also deficient. This investigation combines findings of eight molecular genetic studies that include about 400 accessions of both wild and cultivated germplasm, thus providing the largest assessment of diversity in Lablab purpureus to date. In particular, results from a recent molecular investigation (Robotham and Chapman 2015) are revisited and reinterpreted by integrating them with known phenotypic diversity. Wild accessions clearly fall into two types, with characteristic pods-2-seeded and 4-seeded. The large majority of cultivated types are more closely related to 4-seeded pod-types. Certain cultivated 2-seeded pod-type accessions from Ethiopia are genetically closer to wild 2-seeded pod-types. These two major phenotypes are reflected in two chloroplast DNA haplotypes A and B. Hence, two domestication events appear to exist in L. purpureus based on this combined data. No other geographic patterns of diversity, which might assist to trace the dispersal of L. purpureus, were found as cultivated accessions predominantly fell into 2-3 major groups. In all studies, the greatest genetic diversity was found in Africa, making Ethiopia one of the probable centers of domestication.