RFLP DIVERSITY OF COMMON BEAN (PHASEOLUS-VULGARIS) IN ITS CENTERS OF ORIGIN

Eighty-five wild and cultivated accessions of common bean (Phaseolus v ulgaris L.), representing a wide geographic area in the centres of dom estication were tested for restriction fragment length polymorphisms ( RFLPs). Genomic DNA was digested with one of three restriction enzymes (EcoRI, EcoRV, and HindIII) and hybridized to 12 probes distributed t hroughout the common bean genome. Accessions could be classified into two major groups with a distinct geographical distribution in Middle A merica and the Andes. Within each gene pool, cultivated accessions clu stered together with wild forms from the same geographical area suppor ting the multiple domestications hypothesis for this crop. Estimates o f Nei's genetic distances among the cultivated races from the two diff erent gene pools varied from 0.12 to 0.56 and among races from the sam e gene pool from 0.04 to 0.12, suggesting that the divergence in Phase olus vulgaris has reached the subspecies level. The level of genetic d iversity (H-t = 0.38) was twice the value obtained with isozyme analys is. Genetic diversity within races (H-s = 0.27) was four to five times higher compared with isozymes, but genetic diversity between races (D -st = 0.11) was similar for both categories of markers. These results corroborate previous studies on the characterization of genetic divers ity in common bean that clearly showed two distinct gene pools, Middle American and Andean. Moreover, RFLP markers are superior to isozymes because they provide better coverage of the genome and reveal higher l evel of polymorphisms.