Suppression of rice seedling rot caused by Burkholderia glumae in nursery soils using culturable bacterial communities from organic farming systems

In this study, we developed an effective and stable technique for suppressing seedling rot of rice caused by Burkholderia glumae using bacterial communities cultured from nursery soils for organic farming (OF) of rice that have disease-suppressive activity. When culturable bacterial communities (CBCs) isolated from OF soils by growth on nutrient-agar (NA, nutrient-rich conditions) medium were added to autoclaved conventional nursery soil, a disease-suppressive effect on seedling rot was observed for some, but not all the CBCs obtained from soil samples. When bacteria were cultured under nutrient-poor conditions (1/1,000 diluted NA medium and 1/1,000 diluted nutrient-gellan gum medium), a disease-suppressive effect was observed more frequently. The disease-suppressive activity was maintained during repeated subculture on nutrient-poor media, but not on nutrient-rich media. These results suggest that CBCs have potential for disease control treatments, depending on their soil source and culture conditions. Analysis of the composition of CBCs suggested that bacteria in the order Burkholderiales may be responsible for the disease-suppressive activity. Correlated with the disease-suppressive effect, furthermore, the bacterial community structures that developed in rhizosphere soils after application of CBCs were stable and resistant to B. glumae invasion. Although culturable bacteria represent only a part of the bacterial populations of OF soils, it is possible that CBC application mimics the disease-suppressive effects of OF soils.