Exogenous Methyl Jasmonate Enhances Chemical Defense in Blumea balsamifera Against Spodoptera litura by Boosting Phenylpropanoid and Flavonoid Metabolism

Blumea balsamifera (L.) DC. is the primary source plant of natural borneol, an important ethnic medicine in China. But its quality and yield are severely threatened by the polyphagous pest Spodoptera litura Fabricius during cultivation. In order to elucidate the mechanism of the chemical defense response induced by methyl jasmonate (MeJA) in B. balsamifera plants against S. litura. This study investigated the MeJA-mediated chemical defense in B. balsamifera against S. litura by integrating insect bioassays, enzymatic analysis, and metabolomics. Results demonstrated that exogenous MeJA application significantly inhibited larval feeding preference and consumption, suppressed relative growth rates, and reduced pupal weights. Physiologically, MeJA treatment rapidly upregulated the activities of jasmonic acid (JA) biosynthetic and antioxidant enzymes. Crucially, metabolomic profiling revealed that MeJA triggered a metabolic reconfiguration, specifically promoting the accumulation of defensive secondary metabolites. Notably, key bioactive compounds, including secoisolariciresinol diglucoside and isochlorogenic acid C, were significantly enriched alongside elevated endogenous JA levels. These findings suggest that MeJA enhances the resistance of B. balsamifera not merely by activating enzymatic defense but by reprogramming the phenylpropanoid and phenolic metabolic pathways. The above results indicate that exogenous MeJA can induce the activation of the chemical defense system in B. balsamifera plants and enhance their resistance to S. litura.