PHYSICAL MAPPING OF REPETITIVE DNA-SEQUENCES AND 5S AND 18S-26S RDNA IN 5 WILD-SPECIES OF THE GENUS HORDEUM

The genetic relationships between several wild species and subspecies of the genus Hordeum were assessed using fluorescence in situ hybridiz ation (FISH). Plant material included natural populations of wild barl ey growing in Spain of the annual species, H. marinum ssp. marinum (2n = 14) and gussoneanum (2n = 14), and H. murinum ssp. murinum (2n = 28 ), and leporinum (2n = 28) and the perennial species H. bulbosum (2n = 14) and H. secalinum (2n = 28), plus the South American perennial spe cies H. chilense (2n = 14). FISH was used to locate the chromosomal si tes of two rDNA multigene families 5S and 18S-26S (pTa71 and pTa794) a nd three repetitive DNA sequences (pSc119.2, pAs1 and pHch950) isolate d from different species and genera. The seven chromosomes of the dipl oid species were readily distinguished by their external morphology an d hybridization patterns to pTa71, pTa794, pSc119.2 and pAs1. These DN A probes were also useful for the identification of homologous chromos omes and in differentiating these from unidentified chromosomes in the tetraploid taxa. The use of the probe pHch950 permitted intergenomic differentiation in tetraploids and supports the diphyletic origin of H . murinum and H. secalinum. The in site experiments yielded the follow ing conclusions: (1) differences between the subspecies marinum and gu ssoneanum; (2) close relationships between the subspecies murinum and leporinum; and (3) major differences in physical mapping between H. bu lbosum and the remaining taxa. The genomic and phylogenetic relationsh ips between taxa, as inferred from the results, are discussed.