Bacillus velezensis B313-6 as a Potential Biocontrol Strain Against Anthracnose of Panax quinquefolius, and Its Fermentation Optimization, and Field Efficacy on American Ginseng

Anthracnose of American ginseng is caused by Colletotrichum panacicola. In this study, Bacillus velezensis B313-6, isolated from the rhizosphere soil of American ginseng, was identified based on morphological, physiological, biochemical, 16S rRNA, and the gyrase subunit A protein (gyrA) regions’ analyses. B. velezensis B313-6 showed strong antagonistic activity against C. panacicola with an inhibition rate of 94.4% in dual culture assay, and exhibited broad-spectrum antifungal activity against eight other plant pathogenic fungi (inhibition rates 70–94%). Using single-factor experiments combined with response surface methodology, the fermentation conditions were optimized, increasing the inhibition rate against C. panacicola from 93.9% to 97.4%. In field trials, the B. velezensis B313-6 fermentation broth at a low dose (33.3 mL/m2) provided a control efficacy of 67.6% after the third spray, comparable to a commercial B. subtilis product used as a positive control. The low-dose treatment also significantly promoted American ginseng growth, increasing plant height, root length, shoot fresh weight and root fresh weight by 9.7%, 11.3%, 10.5% and 15.5%, respectively, compared to the treatment of water. These results indicate that B. velezensis B313-6 has great potential as a biocontrol agent against the anthracnose of Panax quinquefolius and also promotes the growth of American ginseng.