Characterization of autochthone biological control agents for pear protection against the brown spot of pear disease caused by Stemphylium vesicarium

Stemphylium vesicarium is an important phytopathogen for many plant species, that switches between necrotrophic and saprophytic lifestyles. In the last decade, it has severely affected pear production worldwide, causing the so-called brown spot of pears (BSP), which led to the replacement of several pear orchards in northern Italy with consequent important economic losses. In the field, the management of the disease still relies on fungicide application, though several resistant genotypes of the pathogen emerged through the years. In the present study, three different bacterial species have been isolated from an infected orchard and evaluated as potential biological control agents (BCAs) against a local isolate of Stemphylium vesicarium. Two bacterial isolates belonging to the Bacillus genus demonstrated a significant ability to inhibit S. vesicarium growth in vitro, both through direct antagonism and the emission of volatile organic compounds (VOCs). The cell-free supernatant from one of these isolates exhibited a strong biocontrol activity, particularly through compounds extracted in acidic conditions. The protective effectiveness of the two most promising BCAs was further validated on detached pear fruits infected with S. vesicarium. Overall, the findings suggest that these two BCAs have the potential to be developed into a bio-based alternative to fungicides to control BSP, thus contributing to a more sustainable pear production.