Mitochondrial restriction fragment length polymorphisms in wild Phaseolus vulgaris L.: insights on the domestication of the common bean.

Previous examination of intraspecific mitochondrial DNA (mtDNA) diversity in common bean, Phaseolus vulgaris, showed that five restriction fragment length polymorphisms (RFLPs) distinguish the mitochondrial genomes of the two major gene pools of cultivated beans, the Mesoamerican and the Andean. In the study presented here, mtDNA was used to compare the amount of diversity in cultivated beans to that in collections of wild beans to gain an understanding of how and when the mitochondrial genomes of the gene pools became distinct. The mtDNA of six wild bean accessions from Central and South America were digested with nine restriction endonucleases and analyzed by Southern hybridization. A total of twenty RFLPs were detected demonstrating a significantly higher amount of mtDNA variability in wild beans than in cultivated ones. All of the wild beans had the same mtDNA pattern for four out of the five inter-gene pool RFLPs, indicating that the polymorphism arose soon after domestication: two in the gene pool of the cultivated Mesoamerican beans and two in the gene pool of the cultivated Andean beans. The fifth RFLP must have occurred before domestication since the locus was also polymorphic in the wild beans. Wild beans from the south Andes were distinct and less variable than wild accessions of the north Andes and Mesoamerica. The distribution of mtDNA RFLPs among the wild beans supports the concept of two distinct domestication events for P. vulgaris.