Origin and domestication of the common bean (Phaseolus vulgaris L.).

Information about the level and structure of genetic diversity of crop plants and their wild relatives gathered during evolutionary studies is of fundamental importance for modern crop and animal improvement. Indeed, the starting point in any breeding project is the identification of the available genetic variation, which represents the raw materials for the selection and development of new cultivars. Phaseolus vulgaris is characterised by two geographic gene pools, one located in Mesoamerica and the second in the southern Andes, with parallel geographic structures in their wild and domesticated beans. In the 1980s, a wild P. vulgaris population was discovered in Ecuador and northern Peru, which was described as a new distinct wild gene pool. This population was suggested to be the ancestral populations of the common bean on the basis of sequence studies of the genes coding for phaseolin, the main seed-storage protein. The occurrence of independent domestication events in Mesoamerica and the Andes is well established; however, the number of domestication events that occurred in the two different regions remains a topic of discussion. We have carried out various studies using multilocus molecular markers with the wild and domesticated genotypes of the common bean, including an analysis of the structure of the European landraces. Recently, we analysed a representative panel containing both wild and domesticated P. vulgaris (215 accessions overall) at the nucleotide diversity level, for five independent genes. Moreover, we analysed the effects of domestication in Mesoamerica on the nucleotide diversity of 48 loci. Here, we present a summary of the results obtained from these studies, with particular focus on the origin of the species and the effects of domestication on the common bean genome. Our data indicate a new scenario for the structure and evolution of wild P. vulgaris, especially questioning the Peru-Ecuador origin, and arguing in favour of a Mesoamerican origin of the species. Moreover, the data support the occurrence of a single domestication event in Mesoamerica, and they also tend to support the same scenario in the Andes.