On the allopolyploid origin and genome structure of the closely related species Hordeum secalinum and Hordeum capense inferred by molecular karyotyping.

Background and Aims: To provide additional information to the many phylogenetic analyses conducted within Hordeum , here the origin and interspecific affinities of the allotetraploids Hordeum secalinum and Hordeum capense were analysed by molecular karyotyping. Methods: Karyotypes were determined using genomic in situ hybridization (GISH) to distinguish the sub-genomes and , plus fluorescence in situ hybridization (FISH)/non-denaturing (ND)-FISH to determine the distribution of ten tandem repetitive DNA sequences and thus provide chromosome markers. Key Results: Each chromosome pair in the six accessions analysed was identified, allowing the establishment of homologous and putative homeologous relationships. The low-level polymorphism observed among the H. secalinum accessions contrasted with the divergence recorded for the sub-genome of the H. capense accessions. Although accession H335 carries an intergenomic translocation, its chromosome structure was indistinguishable from that of H. secalinum . Conclusion: Hordeum secalinum and H. capense accession H335 share a hybrid origin involving Hordeum marinum subsp. gussoneanum as the genome donor and an unidentified genome progenitor. Hordeum capense accession BCC2062 either diverged, with remodelling of the sub-genome, or its genome was donated by a now extinct ancestor. A scheme of probable evolution shows the intricate pattern of relationships among the Hordeum species carrying the genome (including all H. marinum taxa and the hexaploid Hordeum brachyantherum ).