A new disease found in Japan on bentgrass turf caused by Rhizoctonia oryzae

Abstract

In recent years, a new disease has occurred on golf greens of bentgrass (Agrostis palustris Huds.) during summer season. The typical symptom is a round-shaped patch with characteristic white color. In this study, two isolates of the causal pathogen were subjected to the tests of pathogenicity, cultural behaviors and identification.
(1) Inoculation tests on sods (adult plants) and seedlings of creeping bentgrass in the pots revealed that both isolates were pathogenic at the temperature range of 15 to 30°C; and the degree of the damage was severe at 25 and 30°C.
(2) Behaviors of mycelial growth of both isolates were compared on 5 cultural agar media. Mycelial growth was abundunt on PDA, corn meal and oat meal agar media. Sclerotia formation was abundunt on PDA, while no sclerotia formation was observed on Czapek agar medium.
(3) Mycelial growth on PDA was evident in the range of 10 to 35°C and was maximum at 25 and 30°C. There was no significant differences between the isolates and the pathogen of a brown patch pathogen. Both isolates formed salmon coloured irregular sclerotia, in contrast the brown patch pathogens formed regular round shaped brown sclerotia. The hyphal anastomosis of the isolates was observed with R. oryzae and R. zeae, but not with the 15 representative isolates of other anastmosis groups of R.solani. Based on these results, two isolates were identified as Rhizoctonia oryzae Ryker et Gooch.
(4) Inhibition of mycelial growth was observed on PDA agar plates containig 13 fungicides. Chemicals most effective (ED₅₀<0.lppm) were diclomezine, flutolanil, mepronil, tolclofos-methyl, polyoxin D, propiconazole and TPN (ED₅₀<0.1ppm) for both isolates. Benomyl and pencycuron were less effective (ED₅₀>10ppm) .