Weather based Statistical Modelling for Forecasting of Yearly Spot Blotch Severity in different Growth Stages of Wheat

The Objective of the present study was to develop regression models for forecasting spot blotch severity in susceptible and resistant genotypes of wheat crop under Irrigated timely sown condition (ITS), Irrigated late sown condition (ILS) and Rainfed timely sown condition (RFTS). CRI, tillering, jointing, flowering, milking and dough stages of wheat were considered for studying the effect of weather parameters on yearly spot blotch severity. Yearly disease severity data and weekly weather data during the period 1975 to 2012 of North eastern plains zones of India were used for this purpose. On the basis of 37 years data, the correlation coefficients between the yearly spot blotch severity and weekly weather parameters (Maximum temperature, maximum relative humidity and their joint effects) were calculated for measuring the quantitative relationship between these variables. These values of correlation coefficients were used for developing weighted weather indices of weather parameters. Values of r_Tw and r_TRHw were found higher and positive in between jointing stage and flowering stage in both the genotypes. The lower RMSE value of MLR models at jointing stage suggested that forecasted value at jointing stage is more precise than other stages.

Duration between 8* week and ll"¹ week from the date of sowing was found critical for the spot blotch progression in wheat. In this consideration best management practices are required during this duration to restrict the progression of spot blotch. The forecasted values of yearly spot blotch severity in susceptible genotype for the period 2016–17 were obtained as 73.08%, 75.01% and 52.00% for ITS, ILS and RFTS sowing conditions respectively. For the same period forecasted values of spot blotch disease severity were obtained as 37.95%, 43.91% and 38.60% for ITS, ILS and RFTS conditions respectively in the case of resistant genotypes.