Antifungal activity of surfactin produced by <i>Bacillus subtilis</i> against phytopathogenic fungi in apple and strawberry: an <i>in vitro</i> and <i>in vivo</i> study

Abstract Agricultural losses due to infections caused by phytopathogenic fungi are a threat to global food security. The use of chemical pesticides to combat these pathogens raises environmental concerns, making it necessary to seek more environmentally friendly alternatives. The aim of this work was to evaluate the antimicrobial activity of the cyclic lipopeptide surfactin, produced by Bacillus subtilis isolated from the intestine of honey bees. Specifically, the efficacy of surfactin against the phytopathogenic fungi Monilinia spp. and Aspergillus sp. was examined. First, in vitro assays were performed, showing that surfactin inhibited fungal growth by 88.39% for Monilinia polystroma, 67.40% for Monilinia fructigena, 49.56% for Monilinia laxa, and 33.02% for Aspergillus sp. Subsequent in vivo tests demonstrated its antifungal activity in apples and strawberries. In apples inoculated with M. laxa, surfactin application led to a 67.53% reduction in fungal growth and a 65.71% decrease in disease severity. Moreover, in strawberries, surfactin not only inhibited Aspergillus sp. growth but also extended the fruit’s shelf life, reducing disease severity by 80% after 15 days of storage at 4 °C. Additionally, treated strawberries retained higher firmness (up to 30% increase) and higher sugar content compared to untreated controls. These findings suggest that surfactin has potential applications in integrated pest and disease management as an alternative to agrochemicals, promoting more sustainable agricultural practices.