Abstract

Bacillus subtilis are beneficial organisms that can be used as biological control agents. A total of 62 species of Bacillus were isolated from four condiments (Ogiri, Iru, Okpehe and Dawadawa) and soil samples. The isolates were identified as Bacillus subtilis (44%), Bacillus megaterium (16%), Bacillus licheniformis (14%), Bacillus pumilus (23%) and Bacillus cereus (3%). Nine strains of Bacillus subtilis were selected based on their antifungal activity against some indicator fungi namely; Aspergillus niger, A. flavus, Fusarium oxysporum and Rhizopus stolonifer. As potential bio-control agents, a hazard assessment was conducted on potato tubers and garlic cloves. Only two strains; B. subtilis DB4 and B. subtilis B6 did not cause soft rot disease in the potato tubers and garlic cloves. The optimal conditions for the production of antifungal compounds by B. subtilis DB4 was at pH 6.5, 37°C at 24 h while that of B. subtilis B6 was at neutral pH, 37°C and at 36-48 h. The antifungal activity was optimal in both strains when sucrose was the carbon source. The antifungal activity of B. subtilis DB4 was optimal when casein was the nitrogen source, while that of B. subtilis B6 was optimal when urea was used.

Key words: Bacillus subtilis, antifungal, hazard assessment, optimization.