Molecule Genetic Characterization and Host Specificity of Pyricularia Isolates from Annual Ryegrass in Japan

Motoaki Kusaba, Kenji Hirata, Yoshinori Sumida, Akiko Yamagashira, Hidemi Urata and Hiroshi Yaegashi

A total of 89 isolates from blast disease of annual ryegrass (Lolium multiflorum) in Japan were characterized by DNA analyses and pathogenicity assay. On the basis of sequence variation in the ITS 2 region, isolates from annual ryegrass could not be distinguished from those from Triticum and Eleusine. All of the annual ryegrass isolates, however, possessed Grasshopper, a retrotransposon specific to Eleusine isolates, indicating that the annual ryegrass isolates are closely related to those from Eleusine but still distinct from those from Triticum. Inoculation test showed that, despite the close relationship between these ryegrass isolates and those from Eleusine, all of the annual ryegrass isolates were pathogenic to annual ryegrass but failed to produce susceptibility reactions on finger millet (Eleusine coracana). The results suggested that blast disease in annual ryegrass in Japan is caused by blast fungal isolates that are relatives of the Eleusine isolates but specialized to annual ryegrass in their pathogenicity. To determine an appropriate scientific name for the annual ryegrass pathogen, we used a diagnostic method for species identification, namely PCR amplification of a region of the beta-tubulin gene followed by restriction digestion with HpaII. The study concluded that the annual ryegrass pathogen should be designated Pyricularia oryzae in the anamorph form and Magnaporthe oryzae in the teleomorph and holomorph forms.

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