Random Amplified Polymorphic DNA-Based Analysis of Genetic Diversity and Characterization of Representative Bipolaris oryzae Isolates from 2023–2024

Rice brown spot, caused by Bipolaris oryzae, typically occurs during the rice harvest season and can cause substantial yield losses. In 2023-2024, this disease emerged in rice cultivation areas of Korea. However, the population structure and genetic diversity of B. oryzae isolates remain unclear. Such information is necessary to effectively target and control rice brown spot. Thus, this study aimed to investigate the population structure of 50 B. oryzae isolates collected from the leaves, neck, and panicles of rice infected with brown spot through random amplified polymorphic DNA analysis. Among 140 primers tested, 30 were selected and applied, of which 5 exhibited significant polymorphisms among the isolates. The generated dendrogram revealed five clades with 92% similarity. Group A was the most predominant, comprising 84.0% of the total isolates (42/50), followed by Group C (8.0%, 4/50). Groups B, D, and E each contained one isolate (2%). These isolates were collected from the southern region of Korea and exhibited high genetic similarity (>95%). Two strains from Group A (F1305 and F1318) and one each from Groups B (F1248), C (F1253), D (F1317), and E (F1409) were selected and tested for their mycological characteristics and pathogenicity. Compared with the other strains, F1253, F1317, and F1409 exhibited higher conidial production and caused larger diseased leaf areas in the pathogenicity tests. These results suggest that the B. oryzae isolates that caused rice brown spot in 2023 are genetically homogeneous. This study may serve as a basis for developing targeted control strategies against brown spot.