title: The evolutionary history of sea barley (Hordeum marinum) revealed by comparative physical mapping of repetitive DNA.
abstract: OBJECTIVE
  Hordeum marinum is a species complex that includes the diploid subspecies marinum and both diploid and tetraploid forms of gussoneanum. Their relationships, the rank of the taxa and the origin of the polyploid forms remain points of debate. The present work reports a comparative karyotype analysis of six H. marinum accessions representing all taxa and cytotypes.
  
  
  METHODS
  Karyotypes were determined by analysing the chromosomal distribution of several tandemly repeated sequences, including the Triticeae cloned probes pTa71, pTa794, pAs1 and pSc119·2 and the simple sequence repeats (SSRs) (AG)10, (AAC)5, (AAG)5, (ACT)5 and (ATC)5.
  
  
  RESULTS
  The identification of each chromosome pair in all subspecies and cytotypes is reported for the first time. Homologous relationships are also established. Wide karyotypic differences were detected within marinum accessions. Specific chromosomal markers characterized and differentiated the genomes of marinum and diploid gussoneanum. Two subgenomes were detected in the tetraploids. One of these had the same chromosome complement as diploid gussoneanum; the second subgenome, although similar to the chromosome complement of diploid H. marinum sensu lato, appeared to have no counterpart in the marinum accessions analysed here.
  
  
  CONCLUSIONS
  The tetraploid forms of gussoneanum appear to have come about through a cross between a diploid gussoneanum progenitor and a second, related-but unidentified-diploid ancestor. The results reveal the genome structure of the different H. marinum taxa and demonstrate the allopolyploid origin of the tetraploid forms of gussoneanum.
authors.affiliation: Department of Cell Biology and Genetics, University of Alcalá, 28871 Alcalá de Henares, Madrid, Spain.
authors.forename: Alejandro
authors.initials: A
authors.lastname: Carmona
authors.forename: Eva
authors.initials: E
authors.lastname: Friero
authors.forename: Alfredo
authors.initials: A
authors.lastname: de Bustos
authors.forename: Nicolás
authors.initials: N
authors.lastname: Jouve
authors.forename: Angeles
authors.initials: A
authors.lastname: Cuadrado
mesh_terms: D005075:Biological Evolution; D004171:Diploidy; D001467:Hordeum / Q000235:genetics*; D059785:Karyotype; D020161:Physical Chromosome Mapping; D057891:Tetraploidy
keywords: FISH; Hordeum gussoneanum; Hordeum marinum; ND-FISH; allopolyploids; evolutionary history; sea barley