GENETIC DIVERSITY IN CULTIVATED COMMON BEAN .1. ALLOZYMES

Previous studies using phaseolin seed protein as a marker have revealed that cultivated common bean (Phaseolus vulgaris L.) resulted from multiple domestications in Mesoamerica and in Andean South America. Because these studies were based on variation at a single locus, confirmation was sought by analyzing patterns of diversity at nine polymorphic allozyme loci, all unlinked to the phaseolin locus: ribulose bisphosphate carboxylase, shikimate dehydrogenase, cathodal peroxidase, malic enzyme, malate dehydrogenase (two loci), diaphorase (two loci), and leucine aminopeptidase. A total of 227 landraces representing geographical regions from Mexico to Argentina and Chile were analyzed for these enzyme systems. A crude homogenate of primary leaf or root tissue (depending on enzymes assayed) from five seedlings of each landrace grown in vermiculite was used for starch gel electrophoresis. A cluster analysis based on Nei's genetic distance (D) was performed according to the unweighted paired group method of Sneath and Sokal. Our results confirm the existence of two major groups in cultivated common bean, Mesoamerican vs. Andean American; provide indications of gene flow from wild to cultivated beans; and suggest at least five subgroups within Mesoamerican and four within Andean cultivar groups.