Re-Emergence of Rice Brown Spot Disease Caused by Bipolaris oryzae: Interaction between Climate Variability and Nutritional Stress

Rice brown spot, caused by Bipolaris oryzae (syn. Helminthosporium oryzae; sexual stage Cochliobolus miyabeanus), has re-emerged as a major threat to rice production in Asia, particularly under climate-induced environmental instability. Long recognized as a stress-associated disease, brown spot is tightly regulated by interactions among temperature, humidity, rainfall, leaf wetness duration, and host nutritional status. Recent shifts in seasonal rainfall patterns, rising nighttime temperatures, and increasingly frequent periods of high humidity have created microclimatic conditions that strongly favor pathogen infection, lesion expansion, and sporulation. In parallel, chronic nutrient imbalances in intensively cultivated paddy soils—especially suboptimal availability of nitrogen, phosphorus, potassium, silicon, and key micronutrients—enhance host susceptibility and accelerate foliar senescence, thus creating a physiological niche highly conducive to B. oryzae. In 2025, unusually severe brown spot epidemics were reported across the southern rice-growing regions of Korea, coinciding with extreme rainfall events, prolonged overcast conditions, high relative humidity, and clear evidence of nutrient depletion in long-term rice systems. This mini-review synthesizes current advances in our understanding of pathogen biology, climate drivers, and nutritional ecology, places Korea’s recent outbreaks in a global context of brown spot re-emergence, and discusses plausible mechanisms linking climate and nutrient stress to disease epidemics. Finally, we argue for integrative climate-nutrient-pathogen frameworks and climate-smart nutrient management as central components of future brown spot mitigation strategies.