Potential Action Mechanism and Inhibition Efficacy of Morinda citrifolia Essential Oil and Octanoic Acid against Stagonosporopsis cucurbitacearum Infestations

Abstract

The use of plant-based products has been shown to efficiently inhibit fungi-mediated diseases in agricultural crops. Here, we extracted and evaluated the composition of noni, <i>Morinda citrifolia</i> L., essential oil and assessed its activities against <i>Stagonosporopsis cucurbitacearum</i> in <i>Cucumis melo</i> L. Using in silico molecular approaches, potential interactions between the essential oil major components and <i>S. cucurbitacearum</i> tyrosine-tRNA ligase were predicted. Finally, we also measured the potential interference of plant physiology (the stomatal conductance and net photosynthesis) mediated by the application of the <i>M. citrifolia</i> essential oil. Chromatographic analysis revealed that octanoic acid (75.8%), hexanoic acid (12.8%), and isobutyl pent-4-enyl carbonate (3.1%) were the major essential oil compounds. Octanoic acid and noni essential oil, when used as preventive measures, reduce fungal mycelial growth at a concentration of 5 mg/mL without causing significant damage to the treated leaves, which reinforces their efficacies as preventive tools against <i>S. cucurbitacearum</i>. Molecular docking analyses predicted very stable interactions between the major essential oil constituents and <i>S. cucurbitacearum</i> tyrosine-tRNA ligase, suggesting the interference of these plant-based molecules upon enzyme activation. Octanoic acid and <i>M. citrifolia</i> essential oil at concentrations of 20 mg/mL decreased the stomatal conductance and net photosynthesis rate of melon plants, resulting in robust phytotoxicity. Collectively, our findings indicated that despite the phytotoxicity risks at higher concentrations, <i>M. citrifolia</i> essential oil and octanoic acid, have potential as alternative tools for the integrative management of <i>S. cucurbitacearum</i>.