Near-harvest methyl jasmonate application enhances essential oil yield and citral content in Camphora officinarum Nees ex Wall

Citral-type Camphora officinarum (C. officinarum) exhibits high economic value due to its branch and leaf essential oil enriched with citral, yet the low natural concentration of this compound necessitates urgent strategies to enhance yield and quality. Methyl jasmonate (MeJA), a recognized safe elicitor, stimulates aromatic compound accumulation in plants and promotes monoterpene synthesis in C. officinarum suspension cells. However, it remained unclear whether foliar MeJA application enhances monoterpene biosynthesis in C. officinarum. This study evaluated the effects of near-harvest foliar MeJA application at gradient concentrations 0 μmol/L (control, M0), 100 μmol/L (M100), 250 μmol/L (M250), and 500 μmol/L (M500) on growth, oil gland morphology, and essential oil composition in citral-type C. officinarum. The results demonstrated that: M100 treatment significantly increased plant height, branch biomass, leaf biomass, and total biomass compared to the control M0. M250 treatment induced structural modifications in oil cells, enlarging their diameter and increasing density, resulting in an 11.83% increase in essential oil yield per unit fresh leaf weight. Both M100 and M250 treatments enhanced citral content by 3.6% and 3.31%, respectively, while total essential oil production surged by 12.31% (M100) and 15.46% (M250). Principal component analysis (PCA) collectively demonstrated that 100–250 μmol/L MeJA (M100/M250) represented the optimal induction concentration for enhancing essential oil yield and promoting citral synthesis, whereas 500 μmol/L (M500) induced detrimental osmotic stress. These findings demonstrate that MeJA serves as a safe agricultural regulation approach for enhancing essential oil yield and citral content, offering valuable insights for other aromatic plant species.