In Vivo and In Vitro Grown Lemon-Scented Gum as a Source of Nematicidal Essential Oil Compounds

<i>Corymbia citriodora</i> is a eucalypt tree of significant economic value due to its essential oils (EOs), rich in citronellal, citronellol, and other oxygenated monoterpenes with diverse biological activities. Its EOs show potential for the formulation of biopesticides with a lower impact on the environment and human health. This study evaluated the in vitro nematicidal activity of <i>C. citriodora</i> EOs, obtained from in vivo and in vitro grown plants, and their main volatile compounds against the pinewood nematode (PWN, <i>Bursaphelenchus xylophilus</i>), a major phytosanitary threat. The impact of their main compounds on the environment and human health was assessed using available experimental data and predictions from specialized software. Citronellal and citronellol were the most active EO compounds and exhibited EC₅₀ values comparable to the pesticide emamectin benzoate (0.364 ± 0.009 mg/mL). They also displayed superior safety profiles, with reduced environmental persistence and toxicity to non-target organisms. Furthermore, <i>C. citriodora</i> shoots were efficiently propagated through an in vitro system and their volatile profile was characterized by a dominance of citronellal (64%), and citronellol (10%), which highlights their potential as a scalable and sustainable source of nematicidal compounds. Remarkably, the EO of <i>C. citriodora</i> in vitro shoots was strongly active against the PWN, exhibiting the lowest EC₅₀ (0.239 ± 0.002 mg/mL) obtained. These findings underline the viability of <i>C. citriodora</i> EOs as a promising alternative for sustainable pest management, addressing the urgent need for environmentally friendly and health-conscious biopesticides while providing a renewable approach to nematode control.