RFLP EVALUATION OF 9 MEDICAGO ACCESSIONS REPRESENTING THE ORIGINAL GERMPLASM SOURCES FOR NORTH-AMERICAN ALFALFA CULTIVARS

All alfalfa (Medicago sativa L.) cultivars grown in North America orig inate from nine germplasm sources introduced into the USA from differe nt geographic regions. Nine accessions representing the original germp lasm sources have been developed; however, the level of genetic divers ity within and among these accessions is not known. Genetic diversity of these accessions was estimated by screening DNAs from 12 individual s of each accession, along with bulked samples containing equal amount s of DNA from 4, 6, or all 12 individuals, for nuclear RFLPs revealed by hybridization to 35 cloned alfalfa sequences. One hundred and eight y restriction fragments were scored as present or absent across all in dividuals from all accessions, and genetic similarity estimates (GSEs) of all pair-wise comparisons were calculated from these data. The dat a were also examined by cluster analysis and principal components anal ysis (PCA). Individuals within accessions were highly polymorphic, whe reas very few accession-specific polymorphisms were identified. Althou gh individuals from two sources, M. falcata and Peruvian, formed disti nct clusters, genotypes from the other seven accessions were not clear ly discriminated by analyses of these data. The nondistinctiveness of most of these plant introductions (PIs) could be due to a similar gene tic composition of the initial introductions, intercrossing of the dif ferent sources during maintenance, or genetic shift during maintenance . Based on PCA, bulked DNAs underestimated the level of genetic divers ity both within and between accessions, as compared with estimates der ived from analysis of individual genotypes from each source.