Endophytic Bacteria in Forest Protection: Pseudomonas silvicola Controls Pine Needle Blight in Masson Pine

Pine needle blight of Pinus massoniana caused by pathogens of the Pestalotiopsis genus is a destructive disease worldwide, especially in young forests. Chemical fungicides accelerate the formation of resistant strains among plant pathogenic fungi, which makes microbial biocontrol particularly important. In this study, we identified Neopestalotiopsis camelliae-oleiferae as a new pathogen of pine needle blight in P. massoniana via pathogen isolation, inoculation, pathogenicity assays, morphology observations, and multilocus phylogenetic analyses of the ITS, TEF1, and TUB2 regions. PSM-6, an endophytic bacterium, was subsequently isolated from pine needles and was shown to have excellent antagonistic activity against N. camelliae-oleiferae in vitro. Based on the morphology, physiology, and molecular analysis, we identified this strain as P. silvicola. The extracellular secondary metabolites of PSM-6 were further proven to cause the shrinkage and collapse of pathogen hyphae. The decreased disease index and mortality indicated that pretreatment with PSM-6 may effectively protect pine seedlings from pathogen infection. In addition, PSM-6 exhibited broad-spectrum antifungal activity in several phytopathogenic fungi, including Fusarium graminearum, Botrytis cinerea, and Verticillium dahliae. These findings establish PSM-6 as a promising biocontrol agent, offering an environmentally friendly alternative to chemical fungicides for managing pine needle blight and other fungal diseases.