Tri-kingdom interactions in bamboo microbiomes: mechanisms of pathogen cooperation and implications for disease management.

Multi-kingdom disease complexes, where fungi, bacteria, and viruses interact synergistically, are increasingly recognized as a threat to bamboo, a fast-growing Poaceae lineage of high ecological and economic value. However, the mechanisms regulating tri-kingdom disease synergy in bamboo remain poorly understood. This review addresses a central question: Through which molecular and ecological pathways do pathogens from three kingdoms cooperatively enhance bamboo disease severity? We synthesize four key synergy mechanisms: (1) Facilitation of infection: Fusarium proliferatum hyphae build physical entry points as well as transport channels that assist Erwinia sp. to colonize vascular tissues. (2) Immunosuppression: Bamboo mosaic virus (BaMV; genus Potexvirus, family Alphaflexiviridae) inhibits host RNA silencing through viral-encoded proteins TGBp1 and CP, which bind small RNA's and inhibit amplification by RDR6, thereby establishing a permissive environment for secondary invaders, a mechanism inferred from other Potexvirus systems, as direct co-infection evidence in bamboo is currently unavailable. (3) Metabolic cross-feeding: fungal virulence enhanced by bacterial metabolites (e.g., lipopeptides, siderophores), although metabolic synergy in bamboo has not been demonstrated. (4) Biofilm protection: scanning electron microscopy reveals bacterial biofilm on the fungal hyphae surfaces that protect pathogens against host defenses. Quantitatively, the Fusarium-Erwinia co-infection synergy coefficient of bamboo culm rot is S ≈ 1.8, indicating approximately 80% disease severity. Assuming multiplicative independence among mechanisms, tri-kingdom synergy could exceed S > 3.0, a testable hypothesis. This review identifies the following knowledge gaps: (1) no mycovirus isolated from a bamboo-infecting fungus; (2) no bacteriophage characterized against bamboo bacterial pathogen; (3) no quantified studies involving BaMV; and (4) no genome-wide association studies identifying genetic determinants of synergy. This review proposes that effective biocontrol means disrupting the interfaces of pathogen cooperation - disrupting infection courts, interfering with immunosuppression, chelating iron, and degrading biofilm-rather than introducing beneficial microbes. This review proposes a conceptual framework for cross-kingdom microbial interactions in bamboo-associated microbiomes.