Chemical composition of essential oils of four Eucalyptus species and their phytotoxicity on silverleaf nightshade (Solanum elaeagnifolium Cav.) in Australia

Phytotoxicity and chemical composition of essential oils from four selected Eucalyptus species in Australia were investigated. Essential oils had stronger inhibitory effects on germination and seedling growth of silverleaf nightshade (Solanum elaeagnifolium Cav.) when compared with a commercial eucalyptus oil and with 1,8- cineole. E. salubris oil had the highest inhibition index for silverleaf nightshade germination, root growth and shoot growth, while E. spathulata had the lowest inhibitory effect except root growth. Gas chromatography-mass spectrometry analysis revealed 56 compounds present in E. salubris oil, with 1,8-cineole (57.6 %), a-pinene (10.9 %) and p-cymene (8.3 %) predominant. E. dundasii oil contained 55 identified compounds with 1,8-cineole (65.5 %) and a-pinene (19.9 %) being the richest fractions. There were 56 compounds identified from E. brockwayii oil with a-pinene (31.1 %), isopentyl isovalerate (20.2 %) and 1,8-cineole (16.9 %) as the most abundant components. E. spathulata oil contained 60 compounds, predominantly 1,8-cineole (52.9 %) and a-pinene (31.0 %). Further studyis required to determine the phytoxicity of the individual identified compounds on silverleaf nightshade and whether the observed phytotoxicity is attributable to a single compound or to the synergistic effects of several compounds.