Pre-Exposure to Volatile β-Ocimene Enhances Tomato Antiherbivore Resistance Against Polyphagous Lepidopteran Pest Spodoptera litura (Fabricius)

Herbivore-induced plant volatiles (HIPVs) are well recognized for their ability to recruit natural enemies of insect herbivores; however, their function in priming plant anti-herbivore defenses remains poorly elucidated. Here, we demonstrate that volatile exposure to a commercial β-ocimene isomer mixture (hereinafter referred to as β-ocimene) enhances anti-herbivore defense responses in tomato (Solanum lycopersicum) against the polyphagous lepidopteran pest Spodoptera litura (Fabricius). Larval infestation by S. litura significantly upregulated the expression of ten terpene synthase (TPS) genes that govern the biosynthesis of four dominant monoterpene HIPVs: β-ocimene, (-)-α-phellandrene, myrcene, and limonene. Preliminary bioassays revealed that pre-exposure to these four monoterpenes significantly enhances tomato resistance to S. litura larvae, with β-ocimene exhibiting the most pronounced effect. A 24 h pre-exposure to β-ocimene substantially augmented tomato antiherbivore resistance, and this protective response persisted for up to 10 days. Biochemical and molecular analyses revealed that pre-exposure to β-ocimene elevated the endogenous accumulation of jasmonic acid (JA) and jasmonoyl-isoleucine, along with increased transcript levels of the JA biosynthetic genes LOXD and AOS. Consistently, the JA biosynthesis-deficient mutant spr8 failed to exhibit strengthened antiherbivore resistance upon β-ocimene pre-exposure. Collectively, our results demonstrate that β-ocimene pre-exposure enhances tomato antiherbivore resistance via activating JA biosynthesis, highlighting the potential ecological function of HIPVs in priming plant defense against insect pests.