Responses of Soil Bacteria Communities to Organic Material Application and Their Antagonistic Activity against Diaporthe destruens Causing Sweet Potato Foot Rot Disease

Sweet potato foot rot disease caused by Diaporthe destruens (formerly Plenodomus destruens) severely affects the yield and quality of sweet potatoes. To gain basic knowledge on regulating the pathogen using indigenous soil bacteria, the following organic materials were applied to potted soils collected from a sweet potato field contaminated with D. destruens: Kuroihitomi (compost made from shochu waste and chicken manure), Soil-fine (material made by adsorbing shochu waste on rice bran), and rice bran. Soil samples were periodically collected during an incubation for bacterial colony counts and a community ana-lysis using a meta 16S amplicon ana-lysis. The number of bacterial colonies was significantly higher with the Soil-fine and rice bran treatments and slightly higher with the Kuroihitomi treatment than with a chemical fertilizer as the control, and then gradually decreased over time. An amplicon ana-lysis showed that the Soil-fine and rice bran treatments increased the relative abundance of Streptomycetaceae and Micrococcaceae belonging to Actinobacteria and Burkholderiaceae belonging to Beta-proteobacteria. The Kuroihitomi treatment also increased the relative abundance of Streptomycetaceae. The dominant amplicon sequencing variant (ASV) sequences among these families were affiliated with the genera Kitasatospora, Arthrobacter, and Paraburkholderia. Bacteria with sequences identical to these ASVs were isolated from the incubated soils using selective media for dual culture assays. Bacterial isolates in a cluster of Kitasatospora exhibited antagonistic activity against D. destruens. The present results suggest that combining organic materials with antagonistic bacteria may be an effective approach to regulating the growth of D. destruens.