Bacillus thuringiensis C25 which is rich in cell wall degrading enzymes efficiently controls lettuce drop caused by Sclerotinia minor

Sclerotinia is a phytopathogenic genus of fungi that form sclerotia: black, hard, seed-like functioning bodies. Sclerotinia sclerotiorum and Sclerotinia minor are major threats to vegetable cultivation. In this study, we identified an efficient biocontrol agent against lettuce drop caused by S. minor. Initially, 43 bacterial strains isolated from Sclerotinia-infected field were screened for antifungal effects against S. minor. The selected bacterial strains (i.e. C5 and C25) conferred significant (P < 0.05) inhibition in mycelia growth, formation and viability of sclerotia of S. minor in vitro. Especially, strain C25 significantly (P < 0.05) suppressed the disease severity of lettuce drop caused by S. minor and Sclerotinia sclerotiorum. On the basis of biochemical and genetic analyses, strain C25 was identified as a subspecies of Bacillus thuringiensis. Strain C25 exhibited activities of variety of cell wall degrading enzymes such as proteases, beta-1,3-glucanase, and chitinase. Scanning electron microscopy (SEM) implied that strain C25 induced degeneration, distortion, and rupture of hyphae of S. minor. Conclusively, our study was the first to report that Bacillus thuringiensis significantly suppressed sclerotial diseases by degrading the cell walls of pathogenic fungi, at least in part. Strain C25 would be a potential BCA (biocontrol agent) for the agricultural industry.