P-468 - First Report of Xanthomonas sacchari Causing Bacterial Leaf and Panicle Blight of Rice in USA

Rice (Oryza sativa) plants showing symptoms similar to bacterial leaf and panicle blight diseases were observed and collected from four field plots across southern Louisiana in the summer of 2023. In addition to blight symptoms and water-soaked lesions in the leaves, the most noticeable symptom was the blackening or darkening of the leaf tips, which appeared as either dark spots or streaks. Panicle blight-like symptoms, such as grain discoloration of the rice hulls, were also observed on infected plants. To identify the causal organism, bacteria were isolated from surface sterilized, homogenized rice kernels and inoculated onto antibiotic-supplemented LB agar or CCNT agar. After 72 hours of incubation at 41°C, yellow bacterial colonies were observed on both media. Whole-genome sequence analysis confirmed the causal organism as Xanthomonas sacchari. Koch’s postulate was satisfied by inoculating rice variety Kitaake under greenhouse conditions, where symptoms similar to the original samples were observed in the artificially inoculated rice plants 27 days after inoculation. X. sacchari was reisolated from symptomatic tissues. To our knowledge, this is the first report of X. sacchari causing bacterial panicle and leaf blight of rice in the United States. Further studies to monitor the occurrence of this pathogen in other rice-growing states are crucial, as this new pathogen poses a potential problem for US rice production. Additional experiments will investigate the pathogen’s virulence mechanisms, genetic diversity, and pathogenicity across different US rice varieties.