Biocontrol potential of bacteria associated with second-stage juveniles of Meloidogyne graminicola incubated in rice field soil suspension

Summary Nematicide treatment is the most effective method for controlling root-knot nematodes, but they are being banned to an increasing extent due to their harmful effects on health and the environment. Microbial biocontrol represents a promising strategy in the quest for alternative solutions, and some commercial products have already been developed for this task. Here we attempted to isolate bacteria that control Meloidogyne graminicola , a root-knot nematode that causes yield losses in rice fields throughout Southeast Asia. We thus first closely examined rice field soils with the aim of detecting antagonistic activity against M. graminicola using an in vitro nematode mobility-based assay, followed by a culturomics approach on soil-incubated second-stage juveniles (J2). We identified a soil sample that had a strong antagonistic effect, i.e. , inhibiting M. graminicola J2 mobility by ca 90%. The culturomics approach enabled the isolation of seven J2-associated nematicidal bacteria, which were identified as belonging to the genera Acinetobacter , Agrobacterium , Burkholderia , Micrococcus , Pantoea , Priestia and Sphingomonas . The filtered bacterial culture supernatant had no effect on J2 mobility, indicating a direct interaction between the bacteria and the nematode juveniles. These findings highlighted the promising potential of soil-derived bacteria for the development of sustainable biocontrol strategies against M. graminicola in rice cropping systems.