AOBPreview originally published online on April 13, 2005
Annals of Botany 2005 96(1):23-33; doi:10.1093/aob/mci147
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Ancestry of American Polyploid Hordeum Species with the I Genome Inferred from 5S and 18S–25S rDNA
1 Faculty of Agriculture, Kagawa University, Ikenobe, Miki, Kagawa 761-0795, Japan, 2 Research Institute for Bioresources, Okayama University, Chuo 2-20-1, Kurashiki 710, Japan and 3 Department of Crop Science, Swedish University of Agricultural Sciences, SE-230 53 Alnarp, Sweden
* For correspondence. E-mail staketa{at}ag.kagawa-u.ac.jp
Received: 6 November 2004 Returned for revision: 22 February 2005 Accepted: 28 February 2005 Published electronically: 13 April 2005
• Background and Aims The genus Hordeum exists at three ploidy levels (2x, 4x and 6x) and presents excellent material for investigating the patterns of polyploid evolution in plants. Here the aim was to clarify the ancestry of American polyploid species with the I genome.
• Methods Chromosomal locations of 5S and 18S–25S ribosomal RNA genes were determined by fluorescence in situ hybridization (FISH). In both polyploid and diploid species, variation in 18S–25S rDNA repeated sequences was analysed by the RFLP technique.
• Key Results Six American tetraploid species were divided into two types that differed in the number of rDNA sites and RFLP profiles. Four hexaploid species were similar in number and location of both types of rDNA sites, but the RFLP profiles of 18S–25S rDNA revealed one species, H. arizonicum, with a different ancestry.
• Conclusions Five American perennial tetraploid species appear to be alloploids having the genomes of an Asian diploid H. roshevitzii and an American diploid species. The North American annual tetraploid H. depressum is probably a segmental alloploid combining the two closely related genomes of American diploid species. A hexaploid species, H. arizonicum, involves a diploid species, H. pusillum, in its ancestry; both species share the annual growth habit and are distributed in North America. Polymorphisms of rDNA sites detected by FISH and RFLP analyses provide useful information to infer the phylogenetic relationships of I-genome Hordeum species because of their highly conserved nature during polyploid evolution.
Key words: Chromosome, FISH, genome, Hordeum, in situ hybridization, karyotype evolution, phylogeny, RFLP, ribosomal genes, wild barley
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