Rice rhizosphere bacteria displayed nematicidal activities against the rice root-knot nematode Meloidogyne graminicola

The rice root-knot nematode (Meloidogyne graminicola) is a significant pest affecting rice cultivation, posing a serious threat to rice production across many rice-growing regions. Despite its potential to cause substantial yield losses, effective control measures remain limited, as synthetic pesticides are ineffective, environmentally unsustainable, and not economically viable. In this study, we isolated bacteria from the M. graminicola-infested rice rhizosphere soil from paddy fields in Thailand and identified four potent bacterial antagonists belonging to the genera Bacillus, Sinomonas, and Streptomyces. Using in planta experiments, these isolates demonstrated the ability to reduce root gall formation caused by M. graminicola by up to 58 %. In vivo assays revealed that the isolates exhibited varying levels of lytic enzyme production, including protease, chitinase, collagenase, and lipase. Interestingly, some nematicidal isolates displayed plant growth-promoting traits. Genome-wide phylogenetic analysis identified the isolates as Bacillus rhizoplanae (isolate N1-003), Sinomonas atrocyanea (isolate RET2-001), Streptomyces misionensis (isolate RET4-A007), and Streptomyces rhizoryzae (isolate RET4-A017). Functional analysis revealed a diverse array of orthologs encoding proteins and secondary metabolites with known nematicidal activity. Our results support the hypothesis that bacteria employ multiple mechanisms to antagonize plant-parasitic nematodes.