Extensive introgression of Middle American germplasm into Chilean common bean cultivars

The genetic diversity of 95 representative Chilean common bean (Phaseolus vulgaris L.) landraces was analyzed using phaseolin seed protein and eight isozyme systems as genetic markers. Four types of phaseolin were found, "C", "T", "S" and "H", in decreasing order of frequency. Each type had a different distribution between the Northern and Southern regions of the country. Nei's genetic distance based on isozyme diversity indicated that a high percentage of the total variation found in this sample occurred between landraces and only a small percentage of the variation was detected within populations. Cluster analysis based on Nei's genetic distance and a principal component analysis of isozyme frequencies did not detect a clear association between the geographic distribution of the landraces and their isozyme constitution. However, Nei's genetic distance analysis clustered the bean landraces into two major groups which had a specific isozyme pattern, seed color, and seed size. The genetic analysis also detected a rare polymorphism for the Mdh-2 locus, a null allele at the Diap-2 locus, and polymorphism for the Aco-2 locus. The principal component analysis of isozyme frequencies showed that only 30 percent of the genotypes analyzed were similar to the Andean check and 5 percent of the samples were similar to Middle American check. This finding suggests a high frequency of hybridization between the Middle America and Andean gene pools in cultivated common bean from Chile eng