Impact of Agro-met Conditions and Crop Growth Stages on the Progression of Brown Spot Disease in Basmati Rice

The present study was carried out at Crop Research Centre of SVPUAT Meerut, U.P during three cropping seasons i.e. 2018, 2019 and 2020 using basmati rice as test cultivar. The study was primarily focused upon the combined effect of weather parameters and crop growth stages of rice crop on the progression of brown spot disease. It was noticed that disease was first observed at late vegetative stage in every cropping season viz. 2018, 2019 and 2020 and reached its maximum towards maturity phase of the crop by obtaining total AUDPC’S of 1049.3, 1170.74 and 852.6 respectively. A significant negative correlation between weekly percent disease index (PDI) and T-max & T-min was obtained recording correlation coefficients (r) of (- 0.71 & - 0.98), (- 0.88 & - 0.98) and (- 0.63 & - 0.98) during 2018, 2019 and 2020 respectively indicating decline in maximum and minimum temperatures at the terminal stages of the crop can greatly favor disease progression. A non-significant positive correlation was obtained between weekly m-RH and PDI to the end of every crop season. During the year 2020, a highly significant negative correlation was obtained between weekly a-RH and PDI (r = - 0.803) in contrast with the years 2018 (r = - 0.55) and 2019 (r = -0.477) exhibiting non-significant negative correlation which might be the reason for low PDI during the year 2020 due to greater decline in relative humidity to the end of the crop season. Although, a non-significant negative correlation between weekly PDI and RF (rainfall) and partial positive correlation with weekly bright sunshine hours (BSS) was obtained during all three crop seasons, high intermittent rainfall from late vegetative to reproductive stage during 2018 and 2019 might be responsible for large amount of spore dispersal (high inoculum pressure) leading to greater disease progression. The regression model developed using 2018, 2019 and 2020 meteorological data, which was validated with disease severity data of 2019 yielded significant R2 value of 0.98 using observed and predicted values.