Control of sweet potato Fusarium wilt and black rot by endophytic Bacillus velezensis with improved lipopeptide production.

Background: Sweet potato (Ipomoea batatas) production is threatened by fungal diseases like Fusarium wilt and black rot, causing yield losses. Remedies like fungicides pose environmental and health risks, prompting the need for sustainable biocontrol solutions.

Results: In this study, an endophytic bacterium strain CMML21-49 isolated from sweet potato roots in Naju-si, Korea exhibited strong in vitro antifungal activity against Fusarium oxysporum, Ceratocystis fimbriata, Sclerotinia sclerotiorum, and Rhizoctonia solani. Based on 16S rRNA and gyrB gene sequencing, the strain CMML21-49 was identified as Bacillus velezensis. Lipopeptides (bacillomycin D, fengycin A, surfactin A) were identified by UPLC-QTOF-MS and these crude lipopeptides drove the antifungal effects, achieving strong inhibition of F. oxysporum and C. fimbriata. Optimized culture conditions yielded 0.93 g/L lipopeptides, scaled to 0.96 g/L in a 1.5 kL fermenter, and a spray-dried formulation maintained high viability (6.4-8.9 × 10¹⁰ CFU/g) over six weeks at 4-54℃. Application of CMML21-49 reduced F. oxysporum and C. fimbriata diseased areas in storage root assays and showed 61.54% and 53.85% control efficiencies against Fusarium wilt and black rot, respectively, in field trials. Additionally, postharvest assays achieved over 50% disease reduction by treatment of the strain.

Conclusion: This study presents optimized large scale culture conditions for the B. velezensis strain as well as excellent storage stability and suitability for long-term transport and on-farm use. The findings highlight the B. velezensis strain as a promising and sustainable biocontrol agent, offering a scalable, eco-friendly biocontrol solution for sweet potato fungal diseases.