Surfactin triggers biofilm formation of Bacillus subtilis in melon phylloplane and contributes to the biocontrol activity.

The biocontrol activity of many Bacillus species has been traditionally related to the direct antagonism of pathogens. In previous works, we reported that B. subtilis strain UMAF6614 was an efficient biocontrol agent that produced bacillomycin, fengycin and surfactin lipopeptides.

The antagonistic strain Bacillus subtilis UMAF6639 also confers protection to melon plants against cucurbit powdery mildew by activation of jasmonate- and salicylic acid-dependent defence responses.

Biological control of plant diseases has gained acceptance in recent years. Bacillus subtilis UMAF6639 is an antagonistic strain specifically selected for the efficient control of the cucurbit powdery mildew fungus Podosphaera fusca, which is a major threat to cucurbits worldwide. The antagonistic activity relies on the production of the antifungal compounds iturin and fengycin.

The iturin-like lipopeptides are essential components in the biological control arsenal of Bacillus subtilis against bacterial diseases of cucurbits.

The antibacterial potential of four strains of Bacillus subtilis, UMAF6614, UMAF6619, UMAF6639, and UMAF8561, previously selected on the basis of their antifungal activity and efficacy against cucurbit powdery mildew, was examined. Among these strains, UMAF6614 and UMAF6639 showed the highest antibacterial activity in vitro, especially against Xanthomonas campestris pv. cucurbitae and Pectobacterium carotovorum subsp.