Genetic diversity and ecological distribution ofPhaseolus vulgaris (Fabaceae) in northwestern South America

Our goal was to investigate in more detail wild and cultivated common bean (Phaseolus vulgaris) accessions from northwestern South America (Colombia, Ecuador, and northern Peru) because prior research had shown this region to be the meeting place of the two major gene pools (Middle American and Andean) of common bean. Explorations were conducted in these countries to collect additional materials not represented in germplasm collections. It was possible to identify wild common bean populations in Ecuador and northern Peru, where they had never been described before. In addition, we were able to extend the distribution of wild common bean in Colombia beyond what was known prior to this study. In all areas, the wild common bean habitat had suffered severely from destruction of natural vegetation. In Colombia, wild common beans were found on the Eastern slope of the Andes (in continuation of its distribution in Venezuela), whereas in Ecuador and northern Peru they were found on the western slope of this mountain range. This geographic distribution was correlated with an ecological distribution in relatively dry environments with intermediate temperatures (known as “dry mountain forest”). Isozyme andphaseolin seed protein analyses of the northern Peruvian and Ecuadoran wild populations showed that they were intermediate between the Middle American and Andean gene pools of the species. Phaseolin analyses conducted on landraces of the Upper Magdalena Valley in Colombia showed that Andean domesticates were grown at a higher altitude than Middle American domesticates suggesting that the former are adapted to cooler temperatures. Our observations and results have the following consequences for the understanding and conservation of genetic diversity in common bean and other crops: 1) Our understanding of the distribution of the wild relative of common bean (and other crops) is imperfect and further explorations are needed to more precisely identify and rescue wild ancestral populations; 2) For crops for which the wild ancestor has not yet been identified, it may be worthwhile to conduct additional explorations in conjunction with genetic diversity studies at the molecular level to guide the explorations; 3) Our study shows the benefit for more efficient germplasm conservation which can be derived from the dynamic interplay between field explorations (and other conservation operations) and molecular analyses to determine genetic distances and diversities; 4) The intermediate materials identified in northern Peru and Ecuador may have basic importance to understand the origin of the common bean and an applied role as a bridge between the Middle American and Andean gene pools; and 5) The differential adaptation to temperature of the two major cultivated gene pools may help breeders select genotypes based at least partially on their evolutionary origin.