Survival of Rhizoctonia solani AG-1 IA, the Causal Agent of Rice Sheath Blight, under Different Environmental Conditions

The ability of Rhizoctonia solani AG-1 IA, the causal agent of rice sheath blight, to survive in diseased rice straw and as sclerotia and mycelia was investigated. After storage for 10 months at 4 degrees C, 25 degrees C and non-air-conditioned natural room temperature (NRT, temperature range from 6 degrees C to 35 degrees C), sclerotia placed inside a desiccator, soaked in sterile water or immersed in wet paddy soil were viable. In contrast, only 15% of sclerotia in dry paddy soil survived. Survival of mycelia was severely affected by temperature and humidity. After 10 months in a desiccator at 4 degrees C, 55% of mycelia samples could survive, whereas at 25 degrees C and NRT, mycelial samples survived for only 7 and 5 months, respectively. However, mycelia stored in sterile water at constant temperatures (4 degrees C or 25 degrees C) survived for 10 months. A certain amount of UV radiation had no obvious effect on the survival of sclerotia or mycelia. The survival rate of the fungus in diseased rice straw stored for 16 months could reach 100% at 4 degrees C, 50% at 25 degrees C and 35% at NRT. The survival rates of the pathogen in diseased rice straw buried in dry, wet and flooded paddy soils after 10-month storage at NRT were 75, 100 and 100%, respectively, indicating that soil humidity is a crucial factor for the survival of this fungus.