Inhibitory effects of Bacillus amyloliquefaciens gfj-4 fermentation supernatant and its mixtures with chemical fungicides against Exserohilum turcicum

Objective  To elucidate the inhibitory activities of the secondary metabolites of Bacillus amyloliquefaciens gfj-4 and their mixtures with chemical fungicides against Exserohilum turcicum.

Method  Based on the mycelium growth rate, we determined the effects of different culture and fermentation times of seed broth and fermentation time on the production of antifungal substances, and evaluated the inhibition effects of fermentation supernatant, lipopeptide crude extracts, and mixtures of fermentation supernatant and seven chemical fungicides.

Result  The most suitable incubation time of seed broth was 6 h and the appropriate fermentation time was 72 h. The EC₅₀ against E. turcicum of the fermentation supernatant and lipopeptide crude extract were 0.32 and 0.11 μL·mL^–1, respectively. E. turcicum showed a high sensitivity to difenoconazole, tebuconazole, procymidone and myclobutanil. Among them, difenoconazole had the highest inhibitory activity against E. turcicum with EC₅₀ of 0.10 μg·mL^–1. Themancozeb and thiram had similar inhibitory activities with EC₅₀ of 12.03 and 12.08 μg·mL^–1, respectively. The inhibitory effect of propineb on E. turcicum was the worst with EC₅₀ of 24.73 μg·mL^–1. The gfj-4 fermentation supernatant and difenoconazole had the additive effect, and the mixture with a volume ratio of 3∶7 had the highest toxicity ratio of 1.28. The fermentation supernatant mixed with mancozeb or propineb in a volume ratio of 2∶8 both had the highest toxicity ratio of 1.28 or 1.67, respectively.

Conclusion  B. amyloliquefaciens gfj-4 and its mixture with difenoconazole or propineb have important application values in pesticide reduction and synergism.