Title : Climate-driven surge: Rice brown spot risk rising in Cote d Ivoire
Abstract:
Rice brown spot (RBS), chiefly caused by Bipolaris oryzae, is an escalating threat to rice production across Africa, particularly within the lowland ecosystems that dominate the region, yet the climatic factors driving this disease remain poorly understood. Unlike better-studied diseases such as rice blast, RBS has received limited attention, leaving a critical gap in knowledge needed for effective forecasting and management. To address this gap, we surveyed 99 farmer-managed fields across three major agro-ecological zones in Côte d'Ivoire during both rainy and dry seasons from 2021 to 2022. In each field, we recorded average RBS severity on a 0–5 scale across multiple stands, alongside measurements of air temperature, relative humidity, wind speed, soil moisture, solar radiation, and rainfall. Our analysis identified distinct climatic drivers. Air temperatures exceeding 27°C and wind speeds above 1 m/s consistently suppressed disease development. In contrast, relative humidity over 80%, wet bulb and dew point temperatures ranging from 23–27°C, and soil moisture or wetness between 0.4 and 0.7 strongly favored RBS progression. Across the study period, annual RBS severity rose by 2.47 to 3.46 points, with significantly greater prevalence observed during rainy seasons compared to dry seasons. Regression models based on these drivers, projected future RBS risk under two climate scenarios. Under the moderate emission pathway (SSP2-4.5), RBS severity is expected to peak at 4.33 between 2060 and 2080. Under the high emission scenario (SSP5-8.5), severity could reach as high as 4.9 by the late 21st century, approaching the maximum possible scale of 5. Collectively, these results confirm climate as a dominant driver of RBS risk and reveal a troubling trajectory of intensification. Urgent, climate-adaptive disease management strategies, including resistant varieties, adjusted planting windows, and improved water management—will be essential to protect rice production and food security across Africa.
