Biocontrol potential of endophytic Sphingobium xenophagum J-1 against Fusarium oxysporum causing root rot in Paris polyphylla var. yunnanensis

Paris polyphylla var. yunnanensis (PPY) is a valuable medicinal plant frequently threatened by root rot caused by pathogenic fungi such as Fusarium oxysporum. Traditional chemical control methods pose environmental and resistance risks, highlighting the need for sustainable alternatives. This study investigated the antifungal potential of the endophytic bacterium Sphingobium xenophagum J-1, isolated from healthy PPY, against F. oxysporum in vitro. The ethyl acetate crude extract of J-1 fermentation broth exhibited significant concentration-dependent inhibition of spore germination, with a 94.64% inhibition rate at 12.5 mg/mL. Microscopic and physiological analyses revealed that the extract severely damaged fungal hyphae, causing swelling, fragmentation, cytoplasmic leakage, and intracellular cavitation. Furthermore, the extract appeared to disrupt cell membrane integrity. These findings suggest that J-1 may act through inhibition of spore germination, hyphal degradation, and membrane disruption. This study provides preliminary in vitro evidence that S. xenophagum J-1 exhibits antifungal activity against F. oxysporum. These findings suggest that strain J-1 represents a promising candidate with in vitro antifungal potential, although its biocontrol efficacy in planta remains to be validated through greenhouse and field experiments.