Aerobiology, epidemiology and disease forecasting of false smut disease of rice in West Bengal, India

Abstract

In India, since 2001, false smut disease of rice has been observed in severe form among major rice growing states. This disease is difficult to tackle, because pathogens infect the plant during flowering stage, and the symptoms are only visible after emergence of the panicle. Thus, disease forecasting is necessary to predict the chance of disease in a certain set of conditions. We analysed 3 years of aerobiological data including pathogenic spore (Usti laginoidea virens) concentration over the rice canopy in West Bengal, India. The crop growth stages in both rabi (winter or dry) and kharif (rainy) seasons during which rapid development of false smut disease takes place were also recorded. Multiple regression analysis of per cent disease index values was done using age of the plant, pathogen concentration and meteorological factors. In dry season, the false smut disease severity depends on age of the plant as well as pathogenic spore concentration, while in rainy season, the severity depends upon spore concentration, RH and minT. From all the analysed data, it can be predicted that spore concentration is the common factor for false smut disease incidence and severity in rice. If pathogen concentration is increased by one unit, there will be 0.981 unit increased in the expected value of disease severity. With odds ratio value, it can be assumed that with a change in spore concentration by 1 unit, the odds of "Severe" versus "High" or "Moder ate" or "Low" or "Absent" combined will be 1.1031 times greater, when other variables held constant. The regression model made from the present study would be beneficial to the farmers for early prediction of false smut disease of rice by estimating the spore concen tration over rice canopy in West Bengal, India.