Are phytotoxic effects of Eucalyptus saligna (Myrtaceae) essential oil related to its major compounds

We evaluated whether phytotoxic effects of the essential oil from Eucalyptus saligna Sm. leaf litter were related to its major compounds 1,8-cineole (eucalyptol) and α-pinene. Effects of the essential oil and its major compounds, combined and alone, were tested on germination and growth of the weed Eragrostis plana Ness. Volatile organic compounds (VOCs) emitted from the essential oil were determined in the airspace of Petri dishes during the experimental period. These volatile fractions were obtained by solid-phase microextraction (SPME) followed by gas-chromatography coupled to mass spectrometry (GC-MS). Effects of the oil and its major compounds were also assessed in aqueous solution on coleoptile growth of Triticum aestivum L. The essential oil showed the strongest phytotoxic effects on E. plana, followed by eucalyptol, eucalyptol + α-pinene, and α-pinene. A similar order of phytotoxicity was observed on coleoptile growth of T. aestivum. The proportion of oxygenated monoterpenes increased along the experimental period, mainly eucalyptol, and of monoterpene hydrocarbons diminished in the volatile fractions. We conclude that phytotoxicity of E. saligna leaf litter essential oil may be mainly related to eucalyptol and additive or synergistic effects of other minor compounds. Analysing VOCs emission is relevant to elucidate compounds involved in phytotoxicity of a plant species.