Origin and structure of the European common bean (<i>Phaseolus vulgaris</i> L.) landraces

Domestication of Phaseolus vulgaris L. occurred independently in Mesoamerica and the Andes, giving rise to two highly differentiated gene pools. The pathways of dissemination of beans into Europe were very complex, with several introductions from the New World combined with direct exchanges between European and other Mediterranean countries. In the present study, we have used seven chloroplast microsatellite markers (cpSSRs), and two unlinked nuclear loci: phaseolin and Pv-SHATTERPROOF1. The molecular data were used to assess the genetic structure and the level of diversity of a large collection of European landraces of P. vulgaris (307) in comparison with 94 American genotypes representing the Andean and Mesoamerican gene pools. We then compared the diversity of common bean landraces from Europe (as numbers of alleles, haplotypes, gene diversity and genetic differentiation) with that from the American centres of origin. Our results show that most of the European common bean landraces are of Andean origin and that the bottleneck due to the introduction into the Old World was not as strong as has been previously suggested. Finally our data indicate that in Europe, a significant portion of the bean germplasm has derived from hybridization between the Andean and Mesoamerican gene pools

Beans in Europe: origin and structure of the European landraces of <i>Phaseolus vulgaris</i> L.

This study focuses on the expansion of Phaseolus vulgaris in Europe. The pathways of distribution of beans into and across Europe were very complex, with several introductions from the New World that were combined with direct exchanges between European and other Mediterranean countries. We have analyzed here six chloroplast microsatellite (cpSSR) loci and two unlinked nuclear loci (for phaseolin types and Pv-shatterproof1). We have assessed the genetic structure and level of diversity of a large collection of European landraces of P. vulgaris (307) in comparison to 94 genotypes from the Americas that are representative of the Andean and Mesoamerican gene pools. First, we show that most of the European common bean landraces (67%) are of Andean origin, and that there are no strong differences across European regions for the proportions of the Andean and Mesoamerican gene pools. Moreover, cytoplasmic diversity is evenly distributed across European regions. Secondly, the cytoplasmic bottleneck that was due to the introduction of P. vulgaris into the Old World was very weak or nearly absent. This is in contrast to evidence from nuclear analyses that have suggested a bottleneck of greater intensity. Finally, we estimate that a relatively high proportion of the European bean germplasm (about 44%) was derived from hybridization between the Andean and Mesoamerican gene pools. Moreover, although hybrids are present everywhere in Europe, they show an uneven distribution, with high frequencies in central Europe, and low frequencies in Spain and Italy. On the basis of these data, we suggest that the entire European continent and not only some of the countries therein can be regarded as a secondary diversification center for P. vulgaris. Finally, we outline the relevance of these inter-gene pool hybrids for plant breeding