Weather-Driven Dynamics of Rice Blast Disease in Kerala’s Lowland Rice Ecosystem

Abstract

Rice blast, caused by Pyricularia oryzae, continues to be one of the most devastating diseases of rice and poses a significant threat to crop productivity in the Kuttanad lowland ecosystem of Kerala. To understand the spatial pattern of disease occurrence and its association with microclimatic variables, a field survey was conducted during the Rabi season of 2024–2025 across twenty-one major rice-growing locations. Disease incidence (DI) and Percent Disease Index (PDI) were recorded from randomly selected ten one square meter quadrats in each field. Substantial spatial variation was observed among locations, with DI ranging from 14.57% to 66.42% and PDI from 10.53% to 64.41%, the higher disease level occurring at Kaduthuruthy, Kainakary and Purakkad. Correlation analysis revealed that relative humidity and dew point temperature were strongly and positively associated with DI and PDI, indicating their critical role in promoting conidial germination and infection. Maximum temperature showed a significant negative correlation, signifying its suppressive effect on disease development. Although rainfall was not significantly correlated with DI and PDI, descriptive observations indicated moderate rainfall tended to support higher disease levels compared to extremely low or excessive rainfall, suggesting that rainfall acts mainly as a moisture-supporting factor, and its influence becomes evident only when accompanied by favourable humidity and temperature. The study highlights that the humid microclimate of the Kuttanad tract, characterised by high relative humidity, favourable dew point and moderate temperatures, creates highly conducive environments for blast epidemics during the Rabi season.