Mesoamerica x Ande inter-gene pool hybridization and the introduction bottleneck of the common bean (Phaseolus vulgaris L.) in Europe.

Common bean diversity within and between Mesoamerican and Andean gene pools was compared in 89 landraces from America and 256 landraces from Europe to elucidate the effects of introduction bottleneck and selection for adaptation during the subsequent spread of common bean over the whole Europe. Thirteen highly polymorphic nuclearmicrosatellite (nuSSRs) were used to complement chloroplast microsatellite (cpSSRs) and nuclear markers (phaseolin and Pv-shatterproof1) data from previous studies on theexpansion of Phaseolus vulgaris in Europe. The overall amount of nuclear genetic diversity was the same in America (He = 0.52) and in Europe ( He = 0.51) supporting the hypothesis of not significant bottleneck. The between gene pools variance was much larger in America than in Europe, however in America diversity within both the Mesoamerican and the Andean gene pools was smaller than within the same gene pool in Europe. This shows that the two gene pools are more differentiated in America than in Europe where extensive inter-gene pools hybridization did occur.To distinguish inter-gene pool hybrids from “pure” accessions two different approaches were combined: 1. Bayesian assignments based on nuSSR and 2. cpSSR data.This powerful method detected more intermediate genotypes (hybrids) than were previously identified and their frequency was four times larger in Europe (40.9%) than in America (9.3%). The genetic bottleneck following introduction in Europe estimated only with “pure” accessions was significant and five times larger for Mesoamerican than for Andean germplasm. The frequent inter-gene pool hybridization in the European common beans mitigated the effects on genotypic diversity of the introduction bottleneck of common bean in Europe.