GENETIC DIVERSITY AND ECOLOGICAL DISTRIBUTION OF PHASEOLUS-VULGARIS (FABACEAE) IN NORTHWESTERN SOUTH-AMERICA

Our goal was to investigate in more detail wild and culivated common b ean (Phaseolus vulgaris) accessions from north-western 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 (Midd le American and Andean) of common bean. Explorations were conducted in these countries to collect additional materials not represented in ge rmplasm collections. It was possible to identify wild common bean popu lations in Ecuador and northern Peru, where they had never been descri bed before. In addition, we were able to extend the distribution of wi ld 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 distr ibution in venezuela), whereas in Ecuador and northern Peru they were found on the western slope of this mountain range. This geographic dis tribution was correlated with an ecological distribution in relatively dry environments with intermediate temperatures (known as ''dry mount ain forest''). Isozyme and phaseolin seed protein analyses of the nort hern Peruvian and Ecuadoran wild populations showed that they were int ermediate between the Middle American and Andean gene pools of the spe cies. Phaseolin analyses conducted on landraces of the Upper Magdalena Valley in Colombia showed that Andean domesticates were grown at a hi gher altitude than Middle American domesticates suggesting that the fo rmer 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 understan ding of the distribution of the wild relative of common bean (and othe r crops) is imperfect and further explorations are needed to more prec isely identify and rescue wild ancestral populations; 2) For crops for which the wild ancestor has not yet been identified, it may be worthw hile to conduct additional explorations in conjunction with genetic di versity studies at the molecular level to guide the explorations; 3) O ur study shows the benefit for more efficient germplasm conservation w hich can be derived from the dynamic interplay between field explorati ons (and other conservation operations) and molecular analyses to dete rmine 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 brid ge between the Middle American and Andean gene pools; and 5) The diffe rential adaptation to temperature of the two major cultivated gene poo ls may help breeders select genotypes based at least partially on thei r evolutionary origin.