Role of the rice seedlings and Kouyawarabi (Onoclea sensibilis L.) infested with Burkholderia plantarii as the source of bacterial seedling blight of rice

Abstract

To elucidate the role of Kouyawarabi (Onoclea sensibilis L.), a weed in the environs of paddy fields as an inoculum source of Burkholderia plantarii, the pathogen of bacterial seedling blight of rice, We investigated transmission of the pathogen from the time inoculated rice seedlings were transplanted into fields until seeds were harvested during the next crop season. Although seeds harvested from the diseased transplants were not contaminated, a few infested seeds were harvested from the hills distant to the transplant area. However, the bacterium was not detected from rice stublle the next spring or from seeds harvested from rice plants grown in the sites that held the transplanted diseased seedlings during the previous year. Numerous infested seeds were obtained from rice plants grown in pots irrigated with rainfall runoff from leaves of Kouyawarabi infected with B. plantarii, however, the resultes varied from year to year. To follow the bacterium from the weed to rice plants, we used a rifampicin-resistant strain of the bacterium. The bacterium clearly was carried in the rainfall from lesions on Kouyawarabi leaves, survived in the irrigatation water and was then detected in tissues of rice plants until harvest. Additionally, seedlings that developed from infested rice seeds had typical symptoms of bacterial seedling blight in nursery boxes. Both rice seedlings and Kouyawarabi contaminated with B. plantarii play an important role as inoculum source of bacterial seedling blight of rice during unfavorable weather for growing rice plants.