Wild and cultivated hexaploid oats share the same genomes (AACCDD) and display a considerable level of interspecific variation in both plant and chromosome morphology. The GISH was utilized to detect the interspecific genomic compositions in four hexaploid and two tetraploid oats using total genomic DNA of Avena eriantha (a C-genome diploid) as probe. Intergenomic translocations between A/D and C-genome chromosomes were frequently observed in hexaploid and tetraploid species. In the hexaploid, two pairs of A/D genome segments on C-genome chromosome (A/D-C) translocation and four to six pairs of C-genome segments on A/D genome chromosome (C-A/D) translocation were clearly identified whilst the number of A/D-C translocations was constant among species. In the tetraploid A. maroccana (AACC), a pair of A-C and four pairs of C-A translocations were observed. Moreover, the A/D translocation segments on chromosome 5C was detected only in A. byzantina and A. maroccana, whilst A/D-C translocations were observed on the 1C and 7C of A. sativa, A. fatua and A. sterilis. A. byzantina did however also carry the 1C rearrangement. This result shows that A. byzantina has retained a similar genomic constitution to the tetraploid ancestor of hexaploid oats, A. maroccana. Three pairs of A-C translocations were detected only in A. murphyi (AACC), and two pairs of those were the 1C and 7C as well as the three hexaploid species except A. byzantina.

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 indicated that three pairs of major hybridization sites of the rDNA were located on 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) chromosomes. RFLP analysis of the rDNA sequence fragments identified differences among M55, M71 and M74, whilst M59 and M60 were the same with regard to the four restriction enzyme fragments utilized. M74 always lost single rDNA fragments in four restriction enzyme digests. The RFLP data made it possible to distinguish M55 from M59 and M60 in the northern Haut-Atlas Mountains group. 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