Chemical Profiles and Antifungal Potential of Essential Oils Extracted From the Flower Buds of Eleven Eucalyptus Species

The phytochemical profile of Eucalyptus flower buds (FBs) is not well documented. In this study, we investigated the essential oils (EOs) present in the FBs of 11 Eucalyptus species cultivated in Tunisia. We focused on EO yield via hydrodistillation, chemical composition using GC-MS, and potential antifungal activity. EO yields ranged from 0.71% (Eucalyptus gomphocephala) to 5.3% (Eucalyptus oleosa) (median, 2.9%). Notably, the FBs contained approximately 2.7 times more terpenoids than the leaves. The numbers ranged from 27 (Eucalyptus gracilis) to 40 (E. oleosa). Eucalyptol, α-pinene, para-cymene, aromadendrene, and globulol were present in all species, and their relative abundances enable identification and classification, as confirmed by a principal component analysis (PCA) model. EO of Eucalyptus salubris is the most active against Fusarium oxysporum, whereas Eucalyptus sargentii and Eucalyptus torquata are the most active against Fusarium culmorum and Rhizoctonia solani. Overall, our results suggest that antifungal activity is species-specific and associated with EO composition.