Mating-Type Imbalance Suggests Limited Sexual Reproduction in Field Populations of Bipolaris oryzae in Korea

Mating-Type Imbalance Suggests Limited Sexual Reproduction in Field Populations of Bipolaris oryzae in Korea

Seoyeon Kim1,2, Dongwook Kim3, Taeho Kim3 and Sook-Young Park1,2*

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

3Dept. of Agricultural Life Science, Sunchon National University, Suncheon, Republic of Korea

*Email: spark@scnu.ac.kr

Sexual reproduction can influence the evolutionary dynamics of fungal plant pathogens. In 2025, a severe outbreak of rice brown spot caused by Bipolaris oryzae occurred in Korea. To investigate the population structure of the pathogen during the outbreak, a weekly field survey was conducted over a three-month growing season, yielding 679 isolates. Mating-type analysis identified two idiomorphs, MAT1-1 and MAT1-2. The overall distribution was MAT1-1:MAT1-2 = 288:391 (42.4% vs 57.6%), which significantly deviated from the expected 1:1 ratio (χ² = 15.62, p ≈ 7.7 × 10⁻⁵). Although both mating types were detected throughout the season, the imbalance suggests limited opportunities for random mating. These findings indicate that the outbreak population was likely dominated by clonal propagation rather than frequent sexual recombination. This study provides insight into the population dynamics of B. oryzae during epidemic development in rice fields. (This work was supported by the Rural Development Administration of Korea (RS-2024-00400211))