Genetic diversity of bean (Phaseolus) landraces and wild relatives from the primary centre of origin of the Southern Andes

The Southern Andes, especially the inter-Andean valleys of south Bolivia, is thought to be a probable point of domestication within the primary centre of diversity for Andean common beans (Phaseolus vulgaris L.). The national Phaseolus germplasm collection of Bolivia is maintained by the Pairumani Foundation and consists of 449 accessions where most of the accessions are of common bean but some are of related cultivated and wild species. The goal of this study was to determine the genetic diversity of this collection by sampling 174 accessions of P. vulgaris and an outgroup of eight Phaseolus augusti, two Phaseolus lunatus and one Phaseolus coccineus genotype. The genetic diversity and population structure were estimated using 29 microsatellite markers. High levels of polymorphism were found, with a total of 311 alleles identified and an average of 10.7 alleles per marker. Correspondence analysis and an unweighted pair group method with arithmetic mean-based dendrogram distinguished P. vulgaris from the other species of Phaseolus. Common bean accessions were separated into two groups: the first one including Andean controls and most accessions from high altitudes with morphological characteristics and growth habits typical of this gene pool; the second one including Mesoamerican controls and accessions from low altitudes. Inside the Andean gene pool, the wild accessions were diverse and separated from the weedy and cultivated accessions. Low geographical distances between collection sites (up to 100 km) were shown to be related to low genetic distances. These results are important for the conservation of common beans in the Southern Andes.