Optimization of Nutrient and Fermentation Parameters for Antifungal Activity by Streptomyces lavendulae Xjy and Its Biocontrol Efficacies against Fulvia fulva and Botryosphaeria dothidea

This study has been proved that statistical experimental designs offer efficient and feasible approaches for determination of culture medium and fermentation conditions of Streptomyces lavendulae Xjy. Nutrition and cultural conditions have high influence on the antibiotic production of S. lavendulae Xjy. Soya bean meal, NaCl and (NH₄)₂SO₄ were identified as the best ingredients for high antifungal activity of Xjy based on single variable experiments. Using response surface methodology, the best concentrations of medium ingredients were 1.46% soya bean meal, 2.25% NaCl and 1.26% (NH₄)₂SO₄. The potential components were reduced from seven to three, and the antibiotic activity was increased by 10%. The optimized conditions for Xjy in a 250‐ml Erlenmeyer flask were initial pH 5, medium volume 25 ml/250 ml and inoculation volume 10% at 30°C with 200 rpm by response surface methodology. Validation experiments carried out to check the accuracy of the models indicated that the predicted values agreed with the experimental values. The extension of necrosis lesion of Botryosphaeria dothidea was impeded by the application of Xjy in apple fruit. In tomato plants, Xjy showed the 43.7–51.7% curative and protective effects against Fulvia fulva. The optimal medium not only gave a 20% increase in antifungal activity, but it provided a simpler formulation. The results will set a basis for further study on large‐scale fermentation volumes using S. lavendulae Xjy and be useful for the development of more advanced control strategies on plant diseases.