First Report of Rice Bacterial Leaf Blight Caused by <i>Pantoea ananatis</i> in South Korea

In September 2023, bacterial leaf blight-like symptoms were observed on rice (Oryza sativa) cultivated in paddy fields in Goseong (35.054469129°N, 128.366937116°E) and Changwon (35.1124598536°N, 128.3983501826°E), South Korea. In both regions, the disease rate exceeded 70% across the entire paddy field. Since the leaf blight had already progressed, it was impossible to identify the initial symptoms, which are characterized by white striped lesions spreading along the leaf blade. To isolate the pathogen, diseased leaf fragments were surface-disinfected with 70% ethanol for 30 s, washed with sterile distilled water (SDW), ground with a disposable polypropylene grinding rod fitted with a micro-grinding pestle in 1.5-ml e-tubes, suspended with SDW, and serially diluted. The dilutions were spread on trypticase soy agar (TSA) and incubated at 28°C for 48 h. Yellow-colored circular colonies were recovered on TSA, and three colonies (P31a−P31c and P44a−P44c) were isolated from each of the two regions. To identify the isolate, the 16S rRNA gene region was amplified and sequenced using the 27mF/1492mR primer pair. The 16S rRNA gene sequences of isolates from the same region were identical, and those of P31a and P44a (GenBank acc. nos. PZ321509 and PZ321510, respectively) showed the highest homology with the genus Pantoea. Then, based on a previous maximum-likelihood phylogenetic analysis of cpn60 gene sequences from the genus Pantoea, we amplified and sequenced the cpn60 gene from all six isolates using primers cpn60_ent+1 and cpn60_ent-1330 (Bateman et al. 2025). The cpn60 gene sequences of isolates from the same region were identical, and those of the representative isolates, P31a (PZ323262) and P44a (PZ323263), showed 99.59% and 99.66% similarity to the P. ananatis type strain LMG 2665T, respectively. In a maximum-likelihood phylogenetic tree, the bacterium isolated from rice leaf blight was in the same clade as P. ananatis type strain. In addition, P. ananatis-specific PCR analysis was performed using the primer pair PANA_1008 (Asselin et al. 2016), which has high specificity for P. ananatis, to obtain specific amplicons. Therefore, we identified the bacterial isolates as P. ananatis. For the pathogenicity tests, the leaf tips of 4-week-old rice (cultivar Dongjin) seedlings were clipped with scissors dipped in bacterial suspensions (5×10⁸ CFU/ml) of two isolates, P31a and P44a. SDW was used as a negative control. The inoculated rice plants were placed in a growth chamber at 28°C (13 h light/11 h dark). At 5 days after inoculation, water-soaked lesions began to appear on the scissor-cuts, and at 15 days, blight lesions were observed spreading downward from the inoculated sites. No symptoms were observed in the rice treated with SDW. P. ananatis was recovered from the inoculated leaves and confirmed through colony morphology and the cpn60 gene sequencing. Leaf blight of rice caused by P. ananatis was previously reported in several rice-growing regions, including India (Mondal et al. 2011), Africa (Kini et al. 2017), Malaysia (Toh et al. 2019), China (Yu et al. 2021), the United States (Luna et al. 2023), and Venezuela (Mejias et al. 2025), but this is the first report of bacterial leaf blight of P. ananatis in South Korea.