Shoot and root symptoms of rice seedling rot caused by Burkholderia glumae

Abstract Bacterial seedling rot of rice caused by Burkholderia glumae leads to severe seedling blight and results in significant economic losses. Diseased young seedlings typically exhibit browning and chlorosis symptoms on the shoot, which are commonly used to assess disease severity. However, to date, no reproducible method for inducing these symptoms has been reported, and the classification of root symptoms remains unclear. Furthermore, the relationship between shoot and root symptoms has not been elucidated. In this study, we developed a laboratory-based method under controlled conditions to induce the symptoms and classified symptoms appearing on both shoots and roots. We considered six key parameters when developing the method: land race, quantity of infected rice seeds and water volume for seed soaking, temperature at seed soaking, relative humidity and soil characteristics at seedling emergence, and biotron environment. Based on these parameters, we developed a reliable method that reproducibly induces disease symptoms within 12 days from seed soaking. Using this method, we classified six shoot symptoms, and three root symptoms, and one whole-seedling symptom according to severity. Diseased seedlings consistently ceased growth, and the classified symptoms appeared in a reproducible manner. Moreover, the occurrence frequencies of shoot and root symptoms were positively correlated. These findings indicate that the progression of this disease involves a coordinated interaction between shoot and root symptoms.