Optimization of rhamnolipid biosurfactant production from Serratia rubidaea SNAU02 under solid-state fermentation and its biocontrol efficacy against Fusarium wilt of eggplant

Abstract

This work was aimed to explore rhamnolipid production under solid state fermentation using a potential substrate mahua oil cake and to evaluate the biocontrol efficacy of rhamnolipid against Fusarium wilt of eggplant. The combination of Response Surface Methodology and Central Composite Design was employed to optimize higher biosurfactant production. Therefore, four factors viz., substrate concentration, inoculum size, pH and temperature were selected for optimization of rhamnolipid production. The results revealed that the optimum conditions for reduction of surface tension were mahua oil cake 7.78 g, 2.4 ml inoculum size (1 × 10⁸ cells/ml), pH 7 and 30° C temperature. To evaluate the biocontrol efficacy the application of rhamnolipid at various concentrations (0, 100, 250 and 500 μg/ml) by soil and foliar application were employed in the pot culture assay. In vitro study indicated that rhamnolipid producing strain SNAU02 was the most effective antagonist against Fusarium oxysporum f. sp. melongenae and used for pot culture study. On the basis of economic analysis, treatment T₉ (Fusarium oxysporum f. sp. Melongenae ( × 10⁶ spores/ml) + 50 ml of 250 μg biosurfactant/ml to soil + foliar spraying of biosurfactant (250 μg/ml) ranked among the efficacious treatments and was just as effective as a synthetic fungicide. In control treatment, occurrence of disease severity and disease incidence was observed from early stage of crop growth until harvest stage. The pot experiment results indicated that SNAU02 rhamnolipid could be a promising agent in the biocontrol of Fusarium wilt of eggplant, which might help to minimize the yield loss of eggplant.