Herbicide Effect of Greek Oregano Essential Oil on Metabolite Profiles of Target Plants

Origanum vulgare ssp. hirtum (Link) Ietsw. essential oil has been found to possess a wide range of biological activity among which the biocidal properties are particularly valuable in view of the need to use natural products in organic farming. In the present study, attention is focused on the metabolic variations of weeds after treatment with Greek (white) oregano essential oil as a bioherbicide. Dasypyrum villosum (L.) Borbás, Matricaria chamomilla L., Sinapis arvensis L., Lolium perenne L., Trifolium repens L. and Trifolium pratense L. were used as target weeds. The essential oil was applied on weed seedling in the form of an aqueous solution at 5 and 10 µg/mL concentrations by spraying. The effect was reported on the seventh day after treatment and expressed as lethality percentage. The studied Poaceae species were found to be the most resistant, retaining almost 100% of their viability at the both tested concentrations, while the other species at the higher concentration were completely destroyed or significantly damaged. The aerial parts of the surviving individuals of each species were collected and examined by GC/MS for the content of main metabolites. Organic, phenolic, fatty and amino acids, sterols, polyols as well as mono- and disaccharides were identified. Variations in the content of metabolites after treatment with essential oil were observed. The response of treated plants appears to be specific to each species. The results obtained provide data on the use of Greek oregano essential oil as an herbicide in post-emergence stage and complement knowledge of metabolic response of plant to stress factors.