Optimization of medium composition and culture conditions for antifungal activity of a tomato endophytic bacterium

Abstract Early blight of tomato, which is mainly caused by Alternaria solani , is an important, globally distributed disease. We previously isolated an endophytic bacterium (BT4) from healthy tomatoes that has high antifungal activity against A. solani . Industrial applications of antagonistic bacteria require the optimization of culture conditions for growth and antifungal activity. Thus, in this study, the optimum medium composition and culture conditions for BT4 were determined using the “one factor at a time” method and an orthogonal design. Optimal cell growth and maximum antifungal activity were obtained at 30 °C, pH 7.0, with an inoculation proportion of 2% and incubation for 48 h in 12 g/L yeast extract, 10 g/L soluble starch and 7 g/L CaCl 2 in the culture medium. In addition, we compared the antifungal activity of BT4 with iprodione, a contact fungicide that is used on a variety of plants affected by fungal diseases. The results showed that BT4 had antifungal effects that were better than iprodione.