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

Abstract

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 subgenomes Xa and I, 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 Xa 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 Xa genome donor and an unidentified I genome progenitor. Hordeum capense accession BCC2062 either diverged, with remodelling of the Xa sub-genome, or its Xa 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 Xa genome (including all H. marinum taxa and the hexaploid Hordeum brachyantherum).