EVOLUTION OF GENETIC DIVERSITY DURING THE DOMESTICATION OF COMMON-BEAN (PHASEOLUS-VULGARIS L)

M13 DNA fingerprinting was used to determine evolutionary changes that occurred in Latin American germ plasm and USA cultivars of common-bea n (Phaseolus vulgaris L.) during domestication. Linkage mapping experi ments showed that M13-related sequences in the common-bean genome were either located at the distal ends of linkage groups or that they were unlinked to each other or to any previously mapped markers. Levels of polymorphism observed by hybridization with M13 (1 probe-enzyme combi nation) were comparable to those observed by hybridization with single -copy random PstI genomic probes (36 enzyme-probe combinations) but we re higher than those observed for isozymes (10 loci). Results indicate d that the wild ancestor had diverged into two taxa, one distributed i n Middle America (Mexico, Central America, and Colombia) and the other in the Andes (Peru and Argentina); they also suggested separate domes tications in the two areas leading to two cultivated gene pools. Domes tication in both areas led to pronounced reductions in diversity in cu ltivated descendants in Middle America and the Andes. The marked lack of polymorphism within commercial classes of USA cultivars suggests th at the dispersal of cultivars from the centers of origin and subsequen t breeding of improved cultivars led to high levels of genetic uniform ity. To our knowledge, this is the first crop for which this reduction in diversity has been documented with a single type of marker in line ages that span the evolution between wild ancestor and advanced cultiv ars.