Isolation of Pythium species from zoysia grass and their effect on severity of large patch disease

Pythium periplocum, P. rostratum, P. torulosum, and P. vanterpoolii were pr edominant Pythium species isolated from nine sites with a history of large patch disease of zoysia grass. Rhizoctonia solani AG2-2 LP and the Pythium species were isolated from 21 sod samples of zoysia grass exhibiting large patch symptoms in five golf courses. R. solani AG2-2 LP was obtained from a ll samples, while P. periplocum, P. rostratum, P. torulosum, and P. vanterp oolii were obtained from 14, 6, 11, and 8 samples, respectively. At least o ne of the four Pythium species was recovered from 19 samples. To verify pat hogenicity of these four species of Pythium on zoysia grass, they were inoc ulated alone and together with R. solani AG2-2 LP on zoysia grass. When ind ividual isolates were used to inoculate zoysia grass, R. solani AG2-2 LP, P . periplocum, and P. vanterpoolii were moderately aggressive, while P. toru losum and P. rostratum caused little or no disease. Symptoms produced by R. solani AG2-2 LP included orange discoloration of the sheath, and the sheat h was easily pulled from the crown. In periplocum and P. vanterpoolii induc ed only sheath chlorosis, and the sheath was not easily removed from the cr own. In coinoculation tests, the combination of A solani AG2-2 LP and P. to rulosum intensified disease severity on zoysia grass and induced more rapid symptom development than did R. solani AG2-2 LP alone. The combination of R. solani AG2-2 LP and P. periplocum or P. vanterpoolii resulted in sheath necrosis and bare patches, similar to large patch symptoms observed on golf courses.