Biocontrol of olive knot disease by Bacillus subtilis isolated from olive leaves

We evaluated the biocontrol efficacy of a Bacillus subtilis strain isolated from symptomless olive leaves against the olive knot disease pathogen Pseudomonas savastanoi pv. savastanoi. Bacillus subtilis F1 and F-4 displayed antibacterial activity against the pathogen. In planta, only B. subtilis F1 significantly reduced the weight of knots caused by P. savastanoi pv. savastanoi IVIA 1628 and Aw9, whereas copper treatment was effective only when using strain Aw9, thus a reduction of 50% was obtained. Preliminary characterisation of the active compound produced by B. subtilis F1 showed that it was proteinaceous in nature. These results suggest that B. subtilis strain F1 could be used to control, and prevent infection by, the causal agent of olive knot disease.