Chemical composition and bioactivities of Eucalyptus essential oils from selected pure and hybrid species: A review

Eucalyptus spp. are evergreen, tall trees belonging to the Myrtaceae family. They are not only cultivated in many countries for timbers and essential oils, but have also become the focus of scientific innovation through interspecific hybridization. This technique has, in recent decades, been employed to improve the growth and quality of these economically important plants. To date, 10 hybrids have been produced from eight pure species of Eucalyptus. The essential oils of Eucalyptus spp. which are obtained using either hydro-distillation or steam distillation, are rich in phytochemicals like eucalyptol, citronellal, phellandrene, pinene, limonene, and terpineol. The abundance of phytochemicals has contributed to the many biological properties of Eucalyptus spp. essential oils, including antibacterial, antifungal, antioxidant, herbicidal, insecticidal, and repellent activities. This review focused on the phytochemical composition and bioactivities of essential oils from the Eucalyptus hybrids in comparison with the pure species. The essential oils obtained from the hybrids encompass a mixture of components found in the parental species, with some even exhibited more potent bioactivities than the pure species. This review also identified the research gaps on Eucalyptus hybrids and further strengthened the beneficial effects of Eucalyptus essential oils in healthcare, agricultural, nutraceutical, or food industries as well as for pest management strategy.