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 F-1 and F-4 displayed antibacterial activity against the pathogen. In planta, only B. subtilis F-1 significantly reduced the weight of knots caused by P. savastanoi pv. savastanoi IVIA 1628 and Aw(9), whereas copper treatment was effective only when using strain Aw(9), thus a reduction of 50% was obtained. Preliminary characterisation of the active compound produced by B. subtilis F-1 showed that it was proteinaceous in nature. These results suggest that B. subtilis strain F-1 could be used to control, and prevent infection by, the causal agent of olive knot disease.