Chemical composition and phytotoxicity of Eucalyptus parvula (Hill & Johnson) and Melaleuca alternifolia (Cheel) essential oils grown in Tuscany, Italy

The intensification of global agricultural production to meet growing food demand has led to the widespread and often excessive use of synthetic pesticides, raising significant environmental and health concerns. In this context, plant-derived essential oils represent promising natural alternatives. However, the potential of many species remains largely unexplored, particularly regarding their chemical diversity under non-native cultivation contexts. At this regard, our study focused on the chemical characterization of essential oils (EOs) - in terms of yield, composition, and related volatile organic compounds (VOCs) - and on the potential phytotoxic activity of Eucalyptus parvula (Hill & Johnson) and Melaleuca alternifolia (Cheel) grown in Tuscany (Italy). To this end, in M. alternifolia, leaves and fruits collected from 3-and 4-year-old plants were analyzed to investigate age-and organ-related chemical variability, whereas in E. parvula leaf material harvested in March and July was used to evaluate seasonal effects on chemical composition. Phytotoxic activity was also evaluated through germination bioassays performed on several weed species, including L. perenne (L.), S. marianum (L.) Gaertn., R. crispus (L.), and P. hieracioides (L.). Our results revealed that melaleuca EO yield and composition varied with both plant age and organ, with leaves of 4-year-old plants exhibiting higher yields and a greater contribution of oxygenated monoterpenes, mainly 1,8-cineole, whereas fruits had lower yields and a distinct profile enriched in sesquiterpene hydrocarbons. VOC profiles followed similar age-and organ-related trends, and were dominated by monoterpene hydrocarbons such as terpinolene, γ-terpinene, α-terpinene, and 1, 8-cineole. Eucalyptus EO yield showed seasonal variation, while both EO and VOC profiles were dominated by 1,8-cineole with seasonal effects mainly influencing minor constituents. Phytotoxicity assays revealed a dose–dependent response, with increasing percentage inhibition of germination and radicle length as EO doses increased. Although both EOs showed marked inhibitory effects, sensitivity was highly species-specific, as evidenced by differences in IC 50 values. Tea tree EO exerted a stronger phytotoxic effect than eucalyptus EO, inducing higher levels of inhibition at lower doses. So, this study provides new insight on E. parvula and M. alternifolia cultivated under Mediterranean conditions, highlighting their complex chemical profiles and potential use as bioherbicidal agents.