Epidemiology of Cassava Mosaic Disease in the Context of Climate Variability in South East Nigeria

Cassava Mosaic Disease (CMD), caused by African cassava mosaic begomoviruses vectored by Bemisia tabaci, is the most yield-limiting viral disease of cassava in Nigeria. Climate variability has been implicated in altering both B. tabaci population dynamics and CMD epidemic trajectories, yet systematic empirical studies integrating meteorological and epidemiological data from South East Nigeria are absent in the literature. This study examined relationships between seasonal climate variables and CMD epidemic parameters across cassava farms in Enugu, Imo, and Anambra States over three growing seasons from 2021 to 2024. Disease incidence, whitefly population counts, and weather data, including temperature, relative humidity, and rainfall, were recorded at biweekly intervals across 90 sentinel farms. Regression modelling and structural equation modelling were used to identify direct and indirect pathways linking climate variables to CMD epidemic rates. Results indicated that minimum temperature and dry-period length were the strongest predictors of B. tabaci population peaks, which in turn predicted secondary CMD spread rates. Seasons with longer dry spells showed 34 percent higher whitefly densities and 28 percent higher CMD incidence escalation rates compared to wetter seasons. These relationships held across all three states despite variation in mean rainfall. The study provides a statistically robust epidemiological framework for predicting CMD epidemic risk based on seasonal forecasts and contributes original empirical data filling a documented gap in West African plant virology literature. Keywords: Cassava Mosaic Disease, climate variability, Bemisia tabaci, epidemiology, South East Nigeria.