Herbivory Causes Chemical and Biological Changes on Essential Oil from Piper marginatum Leaves

Background: Quantitative and qualitative changes in the plant chemical profiles due to stress-induced response may alter the biological activity of plant tissues. In the current study, we tested the hypothesis that biologic potential against microorganisms of essential oils obtained from Piper marginatum leaves may be affected by herbivore or mechanical injury. Methods: The chemical compositions of the essential oils were determined by GC/MS while antimicrobial activity was determined by disc diffusion method and minimum inhibitory concentration assay. Results: The chemical profile of leaf essential oil of P. marginatum underwent alterations when infested with the grasshopper Xyleus discoideus. The antimicrobial activity of leaf essential oil infested by grasshopper decreased against the microorganisms Bacillus subtilis and Mycobacterium smegmatis, and oil was inactive against the fungus Malassezia furfur. Additionally, the essential oil obtained of P. marginatum leaves subjected to the mechanical damage showed chemical change compared to the oil from the intact leaves but did not cause alterations in the antimicrobial activity of oil. Conclusion: The overall results of this study reveal that P. marginatum leaves respond very clearly to the damages caused by attack by the grasshopper X. discoideus and mechanical damage.