Prefecture, Kyushu, in 1979, which spread quickly until the 1990's, mainly in the southwestern region, and the increased damage spread to the Kanto district in central Japan (Nishimi et al. 2009) . As the disease aggravates relatively high temperatures (approximately 25°C) and causes seedling death and dieback soon after seeding in Italian ryegrass, particularly in early seedings from late summer to early autumn, late seeding after October is recommended to avoid the damage caused by the

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... (Sumida et al. 2003) . However, the detailed reaction to the temperatures of the pathogen is unknown. The pathogen is the same species that causes rice blast, and the rice pathogen attacks ryegrass under favorable conditions (Nishihara 1981). Seedborne transmission is evidenced by the presence of the same ryegrass lineage of the pathogen in the USA and Japan (Tosa et al. 2007 ).