Abstract
A new disease was found on Kentucky bluegrass (Poa pratensis) turf on a golf course in Hokkaido, Japan, from summer through early autumn in 2002 and 2003. Symptoms showed circular patches or rings of brown to tan color ranging from 20 to 40 cm in diameter. Sometimes irregular patches were also found. This disease is characterized by a blackening of roots and rhizomes affected by a disease. Darkly pigmented ectotrophic hyphae and mycelial aggregations were consistently observed on roots and rhizomes. A specific fungus was consistently isolated from roots and rhizomes. Optimal growth rates of the fungus on potato-sucrose agar were between 20 and 25°C. The fungus was found to be pathogenic on Kentucky bluegrass and three other species of cool-season grasses. The fungus was also pathogenic on three species of warm-season grasses. Based on morphological characteristics of pseudothecia, asci and ascospores, the fungus was identified as Ophiosphaerella korrae (J. Walker & A.M. Sm.) Shoemaker & Babcock. We proposed that the name of the new disease on Kentucky bluegrass caused by O. korrae in Japan is ‘necrotic ring spot’ (necrotic ring spotbyo in Japanese) .
