EPIDEMIOLOGICAL INVESTIGATION ON STEM ROT DISEASE OF PADDY CAUSED BY SCLEROTIUM ORYZAE CATT. AT GANGAVATHI, KARNATAKA

Abstract

Stem rot of rice, caused by Sclerotium oryzae Catt., was monitored under natural field conditions at the Agricultural Research Station, Gangavathi, Karnataka, over Kharif 2017-18, Rabi/summer 2017-18 and Kharif 2018-19 using the susceptible cultivar BPT-5204. Disease incidence was recorded weekly together with soil temperature, soil moisture, soil pH, electrical conductivity, rainfall and rainy days. Stem rot appeared consistently in the fifth week after transplanting and increased to 42.00, 36.40 and 38.40% by the seventeenth week in the three seasons, respectively. Maximum soil temperature was strongly and positively associated with disease incidence in Kharif 2017-18 (r = 0.88) and Rabi/summer 2017-18 (r = 0.86), whereas several rainfall, rainy-day and minimum-temperature relationships were negative. Multiple regression and step-down regression identified season-specific combinations of variables, and first-order autoregression closely reproduced observed disease progress (multiple R = 0.995-0.998). The results define a reproducible seasonal window for stem-rot development and provide a basis for weather-linked disease forecasting in irrigated rice.