Unravelling Relationship of Weather Factors with Rice Blast Disease Severity and Development of Prediction Equations

摘要

Magnapoi the oryzae causes rice blast disease, which is one of the most devastating and widespread rice diseases. The present study explores the effects of weather factors (temperature, relative humidity, rainfall and bright sunshine hours) on paddy blast severity. During kharif 2019-20 at Zonal Agricultural Research Station, V. C. Farm, Mandya, seven genotypes were studied viz., Jyothi, Jaya, 1R 64, PAC 837, PAC 837+, CO 39 and HR 12, all of which showed distinct responses to blast disease. The disease started in the 42nd standard meteorological week of 2019 with a mean severity of 1.29 per cent, gradually increasing to a peak in the 3rd standard meteorological week of 2020 (46.14 ). The HR 12 (highly susceptible) genotype showed the highest meandisease severity (64.12 ), whereas the PAC837+ hybrid which is moderately resistant, showed the lowest mean blast severity (3.48 ). The optimal weather conditions for disease development were determined to be maximum temperature (26.75-29.50°C), minimum temperature (16.50-19.25°C), morning relative humidity (80.50 - 94), evening relative humidity (60.10 - 80.50) and sunshine (2.50 - 9.50 hours). According to a correlation study between meteorological factors and disease severity, all the variablesinteracted to play a role in the development of rice blast disease. Further more, the disease development was influenced by the maximum temperature and evening relative humidity. The prediction equations were developed using multiple regression analysisfor all seven genotypes, with coeucients of determination (R2) varying from 66 to 79.70 per cent, indicating that 66 to 77.0 per cent of the total variation in the per cent disease index can be explained by the predicted value of disease severity (PDI).