Optimized Fermentation of Endophytic Bacillus sp. WY17 and WY26 Consortium for Biocontrol of Ginseng Black Spot Disease and Its Antifungal Activity via Crude Protein Extract.

Panax ginseng, a high-value medicinal plant, faces substantial yield losses due to black spot disease, while conventional chemical controls cause pesticide residues and soil ecological damage, necessitating green biocontrol strategies. Here, two antagonistic strains, Bacillus sp. WY17 and WY26, were isolated from the surface-sterilized internal root tissues of 10-year-old ginseng. Through systematic optimization of carbon/nitrogen sources, inorganic salts, and fermentation parameters (temperature, pH, agitation, inoculum size, and duration), the optimal culture conditions were established. The optimal consortium consisted of WY17 and WY26 in a 2:1 ratio (WY17:WY26 = 2:1), which achieved an antifungal inhibition rate of 84.94% against the pathogen compared to the untreated control group (pathogen only). Mechanistic investigations revealed that the crude protein extract exerted its antifungal effect by compromising the integrity of the pathogen's cell membrane, leading to increased permeability and leakage of intra-cellular contents, and produced cell wall-degrading enzymes (chitinase and β-1,3-glucanase), thereby inhibiting mycelial growth and spore germination. In vitro efficacy tests demonstrated that this crude protein extract performed comparably to the chemical fungicide 70% mancozeb, with no statistically significant difference observed between them (p > 0.05). These findings identify a promising compound biocontrol agent derived from indigenous Bacillus strains, offering an effective and environmentally friendly alternative for managing ginseng black spot disease.