Biocontrol Microbial Inoculants Suppress Fusarium oxysporum-Associated Disease Symptoms in Rice and Reshape Multicompartment Microbiomes

Fusarium oxysporum-associated disease symptoms in rice (Oryza sativa L.) seedlings represent an experimentally tractable model for evaluating microbiome-mediated disease suppression under controlled conditions. Biological control of Fusarium-associated disease development in rice provides a promising ecological alternative to chemical fungicides. However, the mechanisms underlying the spatial reconfiguration of the host plant multicompartment microbiome in response to complex inoculants remain insufficiently understood. In this study, we investigated the ability of the monoculture Bacillus amyloliquefaciens Bn1 (B. amyloliquefaciens Bn) and phototrophic–heterotrophic consortia composed of Nostoc sp. J-1 and B. amyloliquefaciens Bn1 to suppress Fusarium oxysporum infection, with parallel profiling of bacterial and fungal communities in rhizosphere soil, the root endosphere, and the phyllosphere using 16S rRNA and ITS amplicon sequencing. Phenotypic screening showed that microbial inoculant application significantly reduced the disease index by up to 55% while maintaining plant dry weight. The protective phenotype was not primarily associated with shifts in alpha diversity, but rather with compartment-specific reorganization of microbial communities. These findings suggest that biological control efficacy was associated less with the overall taxonomic scale of microbiome disturbance than with the formation of a functionally balanced, compartment-specific holobiont architecture but by the formation of a functionally balanced, compartment-specific holobiont architecture, providing a conceptual basis for the targeted design of next-generation phototrophic–heterotrophic biopreparations.