Necrotic ring spot of zoysiagrass in Japan

Abstract

Among the poor growth syndrome of manilagrass (Zoysia matrella), Japanese lawngrass (Z. japonica) and hybrid zoysiagrass (Z. japonica×Z. matrella) turf, that is called ‘shizumi-sho’ in Japanese, we found a new disease in Japan. Symptoms showed circular patches or rings ranging from 10 to 40 cm in diameter. Sometimes irregular patches were also found. This disease is characterized by a blackening of roots and stolons affected by a disease. Darkly pigmented ectotrophic hyphae and mycelial aggregations were consistently observed on roots and stolons. Optimal growth rates on potato-sucrose agar of a fungus which was consistently isolated from roots and stolons were between 20 and 25°C. The fungus was pathogenic on manilagrass, Japanese lawngrass, hybrid bermudagrass (Cynodon dactylon×C. transvaalensis) and four species of cool-season grasses. Pathogenicity of the fungus on manilagrass was higher than that of Phialophora sp. which is known to cause zoysia decline. 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 zoysiagrass caused by O. korrae in Japan is ‘necrotic ring spot’ (necrotic ring spot-byo in Japanese) .