EVIDENCE FOR 2 GENE POOLS OF THE LIMA-BEAN, PHASEOLUS-LUNATUS L, IN THE AMERICA

The lima bean, Phaseolus lunatus L., is a bean species with a broad di stribution in the Americas that rivals that of common bean (P. vulgari s). In order to better understand the organization of genetic diversit y and the pattern of domestication in lima bean, a review was conducte d of the available information on the geographic distribution of wild and cultivated forms of this species. In addition, one-dimensional SDS polyacrylamide gel electrophoresis of seed proteins was also conducte d on a sample of 84 wild, 6 weedy, and 426 cultivated forms. Results s how that wild forms can be divided into two groups, one with smaller s eeds and a very extensive distribution that includes Mexico, Central A merica, and the eastern slope of the Andes, and the other with a more circumscribed distribution on the western slope of the Andes in Ecuado r and northern Peru. Electrophoretic analyses of seed proteins confirm ed this subdivision and, additionally, showed that the large-seeded cu ltivars had been domesticated from the large-seeded wild lima beans in western South America. For the small-seeded lima bean cultivars, it w as not possible to determine a domestication center as the most abunda nt protein pattern in the cultivars also had a widespread distribution in the small-seeded wild progenitor. Electrophoretic analyses showed, however, that domestication led to a reduction of genetic diversity i n the small-seeded, Mesoamerican group, but not in the large-seeded gr oup. The latter may be due to insufficient sampling of the larger-seed ed, wild germplasm.