Phytochemical Profile, Yield, and Antimicrobial Activity of Essential Oils from Eucalyptus camaldulensis, E. grandis, and their Hybrid Clone 2414

Intraspecific hybridization in the Eucalyptus genus offers a strategic pathway for enhancing both essential oil (EO) productivity and bioactivity through chemotype diversification. This study provides a comprehensive comparative analysis of EO yield, chemical composition, and antimicrobial efficacy in Eucalyptus camaldulensis, Eucalyptus grandis, and their interspecific hybrid, clone 2414. Hydrodistillation of leaf material yielded a significantly higher EO output in the hybrid (6.93 ± 0.07% w/w, dry basis) compared to E. camaldulensis (2.47 ± 0.08%) and E. grandis (2.38 ± 0.06%) (p < 0.05). Gas chromatography–mass spectrometry (GC–MS) profiling revealed 46 constituents accounting for over 98% of the total volatile fraction. The hybrid EO exhibited a unique chemotype enriched simultaneously in 1,8-cineole (47,6%) and α-pinene (40,4%), while parental oils displayed a monoterpene dominance with either compound prevailing. Multivariate analyses, including ANOVA and principal component analysis (PCA), confirmed clear chemical differentiation among the taxa and highlighted the hybrid's distinct phytochemical identity. Antimicrobial activity, assessed via broth microdilution assays, demonstrated that the hybrid EO exerted potent inhibitory effects against Escherichia coli, Micrococcus luteus, Staphylococcus aureus, and Bacillus subtilis at 1:100 (v/v), and exhibited enhanced antifungal activity against Coniophora puteana at 1:1000 (v/v), surpassing the efficacy of one or both parental oils. These results suggest a synergistic interaction between major terpenoids (1,8-cineole, α-pinene) and minor compounds such as p-cymene, contributing to the superior bioactivity of the hybrid EO. This study underscores the potential of targeted hybridization in Eucalyptus breeding programs to generate high-yielding chemotypes with broad-spectrum antimicrobial properties. Further investigations on cytotoxicity, seasonal chemical variability, and large-scale feasibility are warranted to advance toward pharmaceutical or industrial applications.