Investigation of the mechanisms involved in the biocontrol activities of natural products from a marine soil bacterium against rice blast

Abstract BACKGROUND Rice blast, caused by Pyricularia oryzae , is a devastating fungal disease threatening global rice production. Overreliance on chemical fungicides has raised environmental concerns and led to resistant strains, necessitating the development of sustainable alternatives. This study integrated marine microbiology and natural antifungal compounds to create eco‐friendly alternatives to chemical fungicides for disease management. RESULTS We identified Pseudomonas aeruginosa R64 with broad‐spectrum antimicrobial activity from mangrove soil in the Mai Po Nature Reserve. The R64 fermentation extract (RFE) exhibited multifaceted inhibition of P. oryzae , suppressing mycelial growth, conidiation, conidial germination and appressorial formation, while disturbing cell wall and membrane function. It also attenuated virulence by impairing appressorial penetration and invasive growth. Further chemical analysis identified phenazines and quinolines as the primary compounds in RFE, corroborated by PCR detection of corresponding phenazine biosynthetic gene clusters. Comparative bioassays with two main bioactive components of RFE, phenazine‐1‐carboxamide (PCN) and phenazine‐1‐carboxylic acid (PCA), against P. oryzae implicated PCN as the principal antifungal effector. RFE and PCN had higher efficacy than tricyclazole in P. oryzae growth inhibition, but were less effective than isoprothiolane. Furthermore, RFE and PCN displayed lower acute ecotoxicity to an environmental indicator organism than isoprothiolane, suggesting their potential as sustainable biopesticides for rice blast management. CONCLUSION Natural products from mangrove soil bacterium P. aeruginosa R64 inhibited key developmental and infection processes of P. oryzae , effectively reducing rice blast development. The promising disease inhibition and low ecotoxicity of mangrove‐associated bacteria highlight their untapped potential for innovative, eco‐friendly fungicide mining for sustainable agriculture. © 2025 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.