The effect of biological control agents on peach fruit infected by Monilinia laxa: biochemical and molecular analyses

Monilinia laxa, responsible for brown rot in peaches, causes significant economic losses. Biological control agents (BCAs) represent a sustainable alternative for managing fungal disease. This study investigated the effect of three commercial formulations, 3Logy® (three essential oils), Serenade®Aso (Bacillus subtilis strain QST 713), and Bio- restore flow (Bacillus spp.), on the antioxidant system (total phenolic and flavonoid content, antioxidant activity) and enzymatic activities (catalase, polyphenol oxidase, phenyl- alanine ammonia lyase) of peaches inoculated with M. laxa. Five days after inoculation, analyses were performed using biochemical assays and RT-qPCR. Tissue samples were collected at 1 cm from the wound and inoculation site. All three formulations reduced disease severity compared to the untreated inoculated control. Serenade®Aso significantly increased total phenolic and flavonoid contents, as well as antioxidant activity. In contrast, the effects of Biorestore flow and 3Logy®were comparable to those observed in the inoculated control sample. These findings were supported by the expression levels of the phenylalanine ammonia lyase gene. Catalase activity increased in fruits treated with Biorestore Flow and 3Logy®, while it was lower in those treated with Serenade®Aso. Considering the expression level of the catalase gene, results suggested the involvement of post-transcriptional regulation mechanisms. The down- regulation of the polyphenol oxidase gene observed in all treatments was associated with a corresponding reduction in enzymatic activity in the treated samples compared to the untreated. These findings highlight the potential of BCAs to enhance peach defense responses against M. laxa, support- ing their use as a sustainable alternative to chemical inputs.