ROLE OF ABIOTIC FACTORS ON THE DEVELOPMENT OF RICE BROWN SPOT CAUSED BY Bipolaris oryzae (BREDA DE HAAN) SHOEMAKER

An attempt was made to study the role of environmental factors on the development of rice brown spot under the agro-ecological condition of red and lateritic belt of West Bengal during the winter season of 2013-2014. The severity of brown spot was increased at a faster rate during the initial period and reached at a maximum level of 5.18% PIPDI (periodical increment in percentage disease index) and 12.7% CIPDI (cumulative increment in percentage disease index) during 3rd and 4th week of September in both of the season. Thereafter, disease was progressed at a lower rate and came down at 0.35% PIPDI during 1st week of November. When maximum average temperature ranged from 32.6 to 34.21°C, minimum average temperature maintained between 23.61°C to 26.18°C, average relative humidity varied between 80.71 to 85.81%, having moderate rainfall, average sunshine of 4.63 to 6.16 kmh-1 and moderate wind speed from 1.0 to 1.57 kmh-1 persist in rice field maximum periodical increment in PDI might be expected. From the R2 value it can be stated that, these six meteorological factors are responsible up to the extent of 85.2% for the development of the disease (cumulative). Similarly, meteorological factors that were regressed on PIPDI could explain the variation up to the extent 53.7%. The present investigation highlighted the actual severity level of brown spot of winter rice. It may also help the farmers for predicting the actual time of disease management and for decision making.