English
Occurrence of Alternaria-Associated Leaf Spot on Rice Under High Temperature and Humidity in Korea
Chawoon Kang1,2, Seoyeon Kim1,2 and Sook-Young Park 1,2
1Department of Plant Medicine, Sunchon National University, Suncheon 57922, Korea
2Interdisciplinary Program in IT-Bio Convergence System (BK21 plus), Sunchon National University, Suncheon 57922, Korea
*Email: spark@scnu.ac.kr
Rice disease surveys conducted from May to October 2025 primarily aimed to monitor blast and brown spot in long-grain rice cultivars in Korea. During the surveys, unusual leaf spot symptoms were observed from late July to early September that differed from typical lesions caused by Magnaporthe oryzae or Bipolaris oryzae. Fungal isolates obtained from symptomatic tissues were consistently identified as Alternaria spp. based on morphological characteristics and ITS sequence analysis. Most isolates were considered saprophytic or weakly pathogenic species, yet they were repeatedly associated with necrotic lesions on living rice leaves. The symptoms occurred during periods of prolonged high temperature and humidity, suggesting that environmental stress conditions may promote opportunistic colonization by Alternaria spp. Later in the season, typical brown spot symptoms caused by B. oryzae appeared and were clearly distinguishable from the earlier lesions. These observations indicate the emergence of Alternaria-associated leaf spot symptoms on rice in Korea and suggest that climatic conditions may influence shifts in fungal communities and disease expression in rice fields. (This work was supported by the Rural Development Administration of Korea, RS-2025-02214096.)
