Phylogeny in the genus Hordeum based on nucleotide sequences closely linked to the vrs1 locus (row number of spikelets)

The phylogenetic relationship between four basic genomes designated H, I, X a, and Xu in the genus Hordeum was studied using a nuclear DNA sequence. Th e sequence, cMWG699, is single copy in the H. vulgare genome, and tightly l inked to the vrs1 locus which controls two- and six-rowed spikes. DNA fragm ents homologous to cMWG699 were amplified from diploid Hordeum species and the nucleotide sequences were determined. A phylogeny based on both base su bstitutions and an insertion-deletion event showed that the H- and Xa-genom e groups are positioned in one monophyletic group indicating that the Xa-ge nome taxa should be included in the H-genome group. The large H-genome grou p is highly homogeneous. The I and Xu genomes are distinctly separated from H and Xa, and form sister groups. Another phylogeny pattern based on data excluding the insertion-deletion gave a result that the Xa genome forms a s ister group to the H-genome group. The difference between the H and Xa geno mes was affected only by a single base insertion-deletion event, thus the H and Xa genomes are likely to be closely related. The I and Xu genomes were again distinctly separated from the H and Xa genomes.