Extent of RFLP variability in tetraploid populations of alfalfa, Medicago sativa

Seven widely-cultivated alfalfa varieties and three ecotypes adapted to Central Italy were used to evaluate the extent of polymorphism in that species. Twenty plants per accession were analysed with 16 RFLP probes combined with three restriction enzymes (48 probe/enzyme combination in total) and the data were used to compute the Nei's similarity index taken as a measure of inter- and intra-population RFLP variability. The varieties were, in general, more homogeneous than the ecotypes and the cultivars ‘Adriana’ and ‘Florida’ could be differentiated more easily than the others. Few accession-specific hybridizing fragments were scored and seven populations could be distinguished from the others on the basis of significant differences in the frequencies of specific fragments. The DNA of plant populations of several sizes was bulked and the ability to detect a given fragment in pooled samples was related to the fraction of plants having that fragment among the plants forming the bulk. The results are discussed with special emphasis on the practical utilization of RFLPs for varietal identification.