Intraspecific variation of 18S-5.8S-26S rDNA sites revealed by FISH and RFLP in wild oat, Avena agadiriana

The tetraploid species Avena agadiriana that was first described in 1985 is distributed on the Atlantic coastal strip south of Casablanca in Morocco. Five accessions of this species (M55, M59, M60, M71 and M74) were compared by using FISH and RFLP analysis of 18S-5.8S-26S rDNA. The FISH data indicat ed that three pairs of major hybridization sites of the rDNA were located o n satellite chromosomes in accessions M55, M59, M60 and M71. Accession M74, however, had only two pairs of major sites of hybridization. A pair of the major rDNA sites in M71 was very small and closely located at the terminal region of Nor-ST (Nucleolar organizing region of subtelocentrics) chromoso mes. RFLP analysis of the rDNA sequence fragments identified differences am ong M55, M71 and M74, whilst M59 and M60 were the same with regard to the f our restriction enzyme fragments utilized. M74 always lost single rDNA frag ments in four restriction enzyme digests. The RFLP data made it possible to distinguish M55 from M59 and M60 in the northern Haut-Atlas Mountains grou p. A unique 20 kb EcoRI fragment characterized M71. Thus, a combination of FISH and RFLP analysis of rDNA was a good tool for inferring intraspecific evolutionary relationship of A. agadiriana.