EXTENSIVE INTROGRESSION OF MIDDLE AMERICAN GERMPLASM INTO CHILEAN COMMON BEAN CULTIVARS

The genetic diversity of 95 representative Chilean common bean (Phaseo lus vulgaris L.) landraces was analyzed using phaseolin seed protein a nd eight isozyme systems as genetic markers. Four types of phaseolin w ere found, ''C'', ''T'', ''S'' and ''H'', in decreasing order of frequ ency. Each type had a different distribution between the Northern and Southern regions of the country. Nei's genetic distance based on isozy me diversity indicated that a high percentage of the total variation f ound in this sample occurred between landraces and only a small percen tage of the variation was detected within populations. Cluster analysi s based on Nei's genetic distance and a principal component analysis o f isozyme frequencies did not detect a clear association between the g eographic distribution of the landraces and their isozyme constitution . However, Nei's genetic distance analysis clustered the bean landrace s into two major groups which had a specific isozyme pattern, seed col or, and seed size. The genetic analysis also detected a rare polymorph ism for the Mdh-2 locus, a null allele at the Diap-2 locus, and polymo rphism for the Aco-2 locus. The principal component analysis of isozym e frequencies showed that only 30% of the genotypes analyzed were simi lar to the Andean check and 5% of the samples were similar to Middle A merican check. This finding suggests a high frequency of hybridization between the Middle America and Andean gene pools in cultivated common bean from Chile.