Crude lipopeptides from culture of Bacillus subtilis strain ET-1 against Podosphaera xanthii on Cucumis melo

The aim of this work was to evaluate the effectiveness of partially purified Iturin A and cell free supernatant (CFS) produced by the Bacillus subtilis strain ET-1 on control of powdery mildew. For this purpose, B. subtilis ET-1 strain was grown in a 21-L stirred-tank bioreactor with 10 litres of an already designed substrate for the production of Iturin A named High Medium Broth (HMB). At the end of culture, an Iturin A amount of 396.86 mg L-1 was determined in the supernatant purified from the cells by centrifugation. Then, the effect of CFS against the cucurbit powdery mildew fungus, Podosphaera xanthii was assessed on plants of Cucumis melo L. (cv Amarillo Oro) in greenhouse and in open-field conditions. For the greenhouse experiments, three different dilutions of supernatant containing 400, 40 and 4 mg L-1 Iturin A were used. Significant dose-dependent control effects were observed. In particular, a control disease of 100% was achieved at the highest concentration tested. In the subsequent open-field trials, a crude lipopeptide extract obtained by acid precipitation was analysed in addition to the CFS. The two conditions were tested at intermediate concentrations containing 100 ppm of Iturin A on plants artificially inoculated with P. xanthii and both showed strong disease control, similar to that observed with chemical fungicide. In conclusion, the results of the present work, while needing further study, open promising scenarios in the use of microbial lipopeptides, like Iturin family, as alternative control agents of plant diseases.