Nuclear and chloroplast microsatellite diversity in Phaseolus vulgaris L. from Sardinia (Italy).

Studies of the level and the structure of the genetic diversity of local varieties of Phaseolus vulgaris are of fundamental importance, both for the management of genetic resources and to improve our understanding of the pathways of dissemination and the evolution of this species in Europe. We have here characterized 73 local bean populations from Sardinia (Italy) using seed traits and molecular markers (phaseolins, nuSSRs and cpSSRs). American landraces and commercial varieties were also included for comparison. We see that: (a) the Sardinian material is distinct from the commercial varieties considered; (b) the variation in the seed traits is high and it mostly occurs among populations (95%); (c) compared to the American sample and the commercial varieties, the Sardinian collection has a low level of diversity; (d) the majority ([95%) of the Sardinian individuals belong to the Andean gene pool; (e) the Sardinian material shows a strong genetic structure, both for cpSSRs and nuSSRs; (f) the nuSSRs and cpSSRs concur in differentiating between gene pools, but a lack of congruence between nuclear and chloroplast has been observed within gene pools; and (g) there are three putative hybrids between the Andean and Mesoamerican gene pools. Despite the relatively low level of diversity, which is probably due to a strong founder effect, the Sardinian landraces are worth being conserved and studied further because of their distinctiveness and because hybridization within and between the gene pools could generate variation that will be useful for breeding.