WEATHER-DRIVEN EPIDEMIOLOGY OF RICE SHEATH BLIGHT (RHIZOCTONIA SOLANI KÜHN): EFFECTS OF TRANSPLANTING DATE AND ENVIRONMENTAL FACTORS ON DISEASE DEVELOPMENT

Abstract

Sheath blight, caused by Rhizoctonia solani Kühn, is one of the most destructive diseases affecting rice production under intensive cultivation. A field study was conducted to evaluate the influence of weather parameters on sheath blight development under different transplanting dates. Disease observations were recorded in a Disease Observation Nursery (DON) using the susceptible rice cultivar 'Swarna'. Three transplanting dates (early, mid, and late) were evaluated, and disease severity was assessed weekly using the IRRI Standard Evaluation System (0–9 scale). Meteorological variables including temperature, relative humidity, rainfall, and bright sunshine hours were correlated with disease progression. Disease initiation occurred during the 33rd, 37th, and 40th Standard Meteorological Weeks (SMW) in early-, mid-, and late-transplanted crops, respectively. Maximum cumulative disease severity reached 33.8, 26.6, and 31.1% during 2022 and 36.6, 28.3, and 33.3% during 2023 in early-, mid-, and late-transplanted crops, respectively. Disease development was favored by maximum temperatures of 30–34°C, morning relative humidity above 88%, and frequent rainfall during the tillering stage. Correlation analysis indicated a positive association of disease severity with maximum temperature (r = 0.16–0.57), bright sunshine hours (r = 0.43–0.74), and morning relative humidity, while minimum temperature (r = −0.65 to −0.86), evening relative humidity (r = −0.61 to −0.79), and rainfall (r = −0.31 to −0.50) were negatively correlated with disease severity. The study demonstrates that early transplanting synchronized susceptible crop stages with favorable weather, resulting in greater sheath blight severity. These findings provide valuable information for disease forecasting and optimizing transplanting schedules for integrated sheath blight management.