Development of a rice tungro epidemiological model for seasonal disease risk management in the Philippines

Abstract

Through an integration of seasonal climate forecasts (SCF) and rice disease epidemiological models, a potential risk for rice disease epidemics can be predicted even before a cropping season starts, allowing agricultural stakeholders to proactively manage risk on a seasonal scale. The objective of this study is to develop and evaluate an epidemiological “rtdSim” model for tungro, a vector-born virus disease of rice, aiming at producing a seasonal tungro risk prediction for the Bicol Region of the Philippines. Given the complex nature of disease pyramid (virus, vector, host, and environment) and their interactions with each other, a simplified model capable of predicting tungro epidemics makes use of assumption-based, simplified model algorithms. The rtdSim calculates the rate of rice hill infection with the rice tungro virus through its vector, the green leafhopper (GLH), using two linked modules: the “GLH population module” simulating complete GLH lifecycle population dynamics and immigration from nearby rice paddies; and the “Tungro virus infection module” simulating virus transmissions between infected rice hills and the GLH vector. The rtdSim is successfully calibrated and validated only for wet season, resulting in a reasonably high level of agreement: a good graphical fit for the incidence level of the disease at 60 days after transplanting and a temporal correlation coefficient of 0.70 between the observed and the simulated epidemics in the Bicol Region. The rtdSim simulations are sensitive to seasonal variations of temperature and rainfall, indicating the potential applicability of the model for seasonal RTD prediction with SCF. The present study highlights the potential for developing a SCF-based early warning system for rice diseases, enabling better decision-making for prevention of potential disease outbreaks on a seasonal scale with integrated pest management (IPM) strategies, e.g. switching to resistant varieties and using synchronous planting, rotations, or fallow periods to avoid peak risk pressure.