RIBOSOMAL DNA REPEAT UNIT POLYMORPHISM IN 49 VICIA SPECIES

DNA restriction endonuclease fragment analysis was used to obtain new information on the genomic organization of Vicia ribosomal DNA (rDNA), more particularly among V. faba and its close relatives and the taxa within three (Narbonensis, Villosa, Sativa) species' complexes. Total genomic DNA of 90 accessions representing 49 Vicia species was restric ted with 11 enzymes, and the restriction fragments were probed with th ree ribosomal clones. Twenty-eight repeat unit length classes were ide ntified. The number of length classes (1-2) per accession did not corr espond to the number of nucleolar organizing regions (NORs). The numbe r of rRNA genes was independent of the 2C nuclear DNA amount present i n the taxon. Each of the 90 accessions had 2 (rarely 1)-4 DraI sites. Those taxa with the same number of DraI sites generally could be disti nguished from each other by different configurations. Probing of the D NA samples digested with tetranucleotide recognition restriction endon ucleases emphasized differences between divergent spacer regions and e nabled relative homologies between the coding regions to be establishe d. Overall, rDNA restriction site variation among the species showed a good correlation with taxonomic classification. The rDNA analysis ind icated evolutionary relatedness of the various taxa within the Narbone nsis species complex. rDNA diversity within two other species complexe s (Villosa, Sativa), on the other hand, was more extensive than expect ed. With few exceptions, data on the two complexes give evidence of ta xon-specific divergences not seen with other approaches. The restricti on site variability and repeat length heterogeneity in the rDNA repeat exhibited startling differences between V. faba and its close wild re latives included in the Narbonensis species complex. This analysis pro vides new evidence that none of the species within the complex can be considered to be putative allies of broad bean.