Allelopathic activity of essential oils from Mediterranean Labiatae

There is a great incentive to discover effective and economically feasible herbicides that are toxicologically and environmentally benign, to replace pesticides that have been withdrawn for regulatory reasons or are ineffective, due to the increasing difficult of managing pest resistance. The study of the physiological role of natural products in biochemical interactions among plants can supply new active compounds and/or models for new mechanisms of action. Volatile terpenes and essential oils have been reported as regulators of germination and growth of other species in several ecosystem. In this study we have carried out a chemical and biological evaluation of the essential oils from eight Mediterranean Labiatae in order to characterize their composition and to verify their potential activities in vitro on growth and development of three test seeds. The essential oils were obtained by hydrodistillation from Hyssopus officinalis L., Lavandula angustifiblia Miller, Majorana hortensis L., Melissa offlicinalis L., Ocimum basilicum L., Origanum vulgare L., Salvia officinalis L., and Thymus vulgaris L. and their chemical composition was achieved by GC and GC/MS methods. The essential oils have been assayed against the germination and the successive radical growth of Raphanus sativus L., Lactuca sativa L. and Lepidium sativum L. The assayed essential oils have shown a good inhibitory avctivity in a dose-dependent way, both on germination and radical elongation of three test species. Our study has shown a positive correlation between the total monoterpene content in the essential oils and the inhibitory activity.