In vitro and in vivo antimicrobial activity of a synthetic capsaicinoid oleoresin against Fusarium oxysporum, Phytophthora capsici, Clavibacter michiganensis and Pseudomonas syringae

Secondary plant metabolites with a specific function are a diverse group of molecules responsible for adapting the plant to its environment. Within the adaptation of plants is the defense against herbivores and pathogens. Among the specialized metabolites is the group of alkaloids, encompassing the capsaicinoids. Capsaicinoids are molecules found in the fruits of the Capsicum genus plants that are responsible for their spicy taste. The main capsaicinoid is capsaicin. Capsaicin has a broad activity spectrum, including antibacterial and antifungal effects. The extraction of specific capsaicinoids from the fruits of Capsicum is complicated, expensive, and of low yield, due to the similarity in the structures. Thus, it is more convenient to synthesize their compounds. This study aimed to evaluate the inhibitory activity of a synthetic capsaicinoid oleoresin (CO, containing 70% nonivamide and 30% dihydrocapsaicin) against single isolates of Fusarium oxysporum Sch and Clavibacter michiganensis Davis (in vitro and in vivo), as well as against Phytophthora capsici Leon. and Pseudomonas syringae Van Hall (in vitro), the former two both in vitro and in vivo, the last two only in vitro. Inhibition of growth of these pathogens ranging from 25.2 to 94.8% was obtained in in vitro assays. In vitro tests were carried out in liquid and solid growth inhibition medium assays for Fusarium oxysporum, Phytophthora capsici, Clavibacter michiganensis and Pseudomonas syringae. In vivo tests used plants of tomato (Solanum lycopersicum) for Clavibacter michiganensis and Fusarium oxysporum. Post-harvest tests were carried out on tomato fruits with natural infections. In vivo tests showed inhibitions from 80.6 to 97.2% and 87.7% in soil for Fusarium oxysporum and in plant for Clavibacter michiganensis, respectively, at concentrations of 0.05 and 0.10% of CO. A significant decrease in damage index was found in plants inoculated with Fusarium oxysporum and Clavibacter michiganensis and treated with CO at 0.05 and 0.10%. Post-harvest tests displayed a significant difference for weight loss and fruit damage due to rotting in the treatment CO 0.05% and 0.20% in comparison to control.

Automated summary

This study evaluated the inhibitory activity of a synthetic capsaicinoid oleoresin against several pathogens and confirmed its antibacterial and antifungal effects through in vitro and in vivo tests. The results showed significant growth inhibition of the pathogens, as well as reduced damage in tomato plants and fruits treated with the synthetic compound.