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, Morinda citrifolia L., essential oil and assessed its activities against Stagonosporopsis cucurbitacearum in Cucumis melo L. Using in silico molecular approaches, potential interactions between the essential oil major components and S. cucurbitacearum 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 M. citrifolia 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 S. cucurbitacearum. Molecular docking analyses predicted very stable interactions between the major essential oil constituents and S. cucurbitacearum tyrosine–tRNA ligase, suggesting the interference of these plant-based molecules upon enzyme activation. Octanoic acid and M. citrifolia 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, M. citrifolia essential oil and octanoic acid, have potential as alternative tools for the integrative management of S. cucurbitacearum.

With the growing demand for sustainable and safe agricultural practices, plant compounds emerge as a solution for biological activities. Here, we evaluated the potential of using Morinda citrifolia essential oil to induce plant resistance and to control phytopathogens (Curvularia lunata) and insect pests (Daubulus maidis). We conducted a chromatographic analysis to unveil the essential oil components. We also quantified the activity levels of antioxidant enzymes and chitinase for resistance induction. The antifungal action was evaluated through disease progression and the inhibition of mycelial growth in addition to in silico studies that made it possible to predict the interaction site between the fungal protein and the compounds. We assessed the toxicity and repellent actions towards the D. maidis. Octanoic acid (58.43%) was identified as the essential oil major compound. Preventive treatment with essential oil and octanoic acid (25.0 µL mL⁻¹) increased not only the plant defense activities (i.e., the activity of the enzymes superoxide dismutase, catalase, phenol peroxidase, ascorbate peroxidase, and chitinase) but also controlled Curvularia leaf spot. The stable interactions between octanoic acid and tyrosine-tRNA ligase from C. lunata suggested protein synthesis inactivation. The essential oil inhibited 51.6% of mycelial growth, and this effect was increased to 75.9% with the addition of adjuvants (i.e., angico gum). The essential oil reduced 76% of the population of D. maidis adults and repelled 50% of the number of D. maidis after 48 h under field conditions. The repellency effect in the field reduced the population of D. maidis adults, transmitters of the stunting complex, by 50%. The results highlight the potential of M. citrifolia as a resistance activator, fungicide, insecticide, and an effective biorational alternative.

The plant Siparuna guianensis is used in traditional medicine and has been the target of studies on the development of new drugs for the control of pests and vector insects. The present study was aimed to evaluate the seasonal influence on the content and composition of the essential oil of S. guianensis. The experiment was conducted for 12 months evaluating the yield of the essential oil of leaves throughout the seasons (autumn, winter, spring and summer). The chemical composition of the essential oil was obtained by gas chromatography-mass spectrometry (GC-MS). The highest oil yield was in autumn and winter, comprising 0.33 and 0.29% (w/w), respectively. The major compound identified was β-myrcene (48.59-24.2%), followed by epicurzerenone (27.24-13.7%) being the most abundant; germacrene D showed lower values of 9.93% in autumn and 13.5-14.34% in the other seasons, besides curzerene that had no production in autumn. The ɣ-elemene component had a higher production of 7.29% in autumn. Compound 2-undecanone did not show significant seasonal changes, with percentages being between 7.26 and 5.43%. The monoterpenes and sesquiterpenes showed similar levels in autumn; however, in the other seasons (winter, spring, and summer), the sesquiterpenes presented higher concentration, reaching 68.54% in summer. The components identified in the essential oil of S. guianensis exhibit interesting biological activities, making this essential oil a promising compound for the development of new biodegradable drugs, repellents, and insecticides. The knowledge about the yield and seasonal composition is fundamental to optimize and maximize the obtainment of compounds of interest for the production of new drugs. Key words: Medicinal plant, negramina, seasonal production, essential oil, gas chromatography-mass spectrometry (GC-MS).