RFLP ANALYSIS OF HORDEUM SPECIES RELATIONSHIPS

Detailed ribosomal DNA restriction maps were prepared for eight representative plants from Hordeum L. Section Hordeum (two H. bulbosum, H. glaucum, a diploid H. leporinum, a tetraploid H. leporinum, H. murinum, H. spontaneum, H. vulgare) in order to explore species relationships. The four restriction enzymes (EcoRI, SacI, BamHI and HindIII) used in our earlier study were supplemented with six additional ones (BglI, ClaI, KpnI, PvuII, SstII and XhoI). Southern blots prepared, using the restriction enzymes singly and in combinations, were probed with the wheat ribosomal probe pTA71, and hybridization patterns analyzed. A comparison of the derived maps with known maps for wheat, pea and pumpkin showed strong conservation of restriction sites, especially in the ribosomal coding region. The maps suggest that duplication of coding region DNA and its insertion into the spacer region as well as amplification of subrepeats are responsible for variation in rDNA repeat length. Phylogenetic analysis indicated the early divergence of ancestral wheat and Hordeum species, followed by the divergence of the progenitors of H. spontaneum/H. vulgare and the remaining Hordeum species and, most recently, between those of H. glaucum and H. murinum.