Synergistic Regulation of Codonopsis pilosula Growth and Metabolism by Trichoderma , Salicylic Acid, and Methyl Jasmonate

Endophytic fungi can mediate salicylic acid (SA) and methyl jasmonate (MeJA)-related signaling in medicinal plants, thereby influencing metabolite synthesis, stress resistance, and growth development. Experimental groups comprised control, Trichoderma longibrachiatum inoculation (FG), FG + SA (FS), FG + MeJA (FM), FG + SA + MeJA (FSM), and corresponding inhibitor treatments (FSI, FMI, FSMI), with I indicating inhibitor application. Morphological traits, photosynthetic parameters, nitrogen metabolism enzyme activities, antioxidant defense indices, and signaling-related molecules in Codonopsis pilosula were measured at 15, 30, and 50 days. Non-targeted metabolomic analysis was conducted to identify differential metabolites and enriched pathways. The results showed that the FSM treatment markedly promoted root development and biomass accumulation in C. pilosula, increased chlorophyll content and photosynthetic rate, and enhanced antioxidant capacity, as reflected by increased CAT and GR activities. Meanwhile, endogenous SA and JA levels were markedly altered, and nitric oxide (NO) levels exhibited treatment-dependent dynamics, suggesting that NO may participate in broader hormone-associated signaling responses during the Trichoderma-SA/MeJA interaction. Metabolomic analysis revealed that FSM notably regulated steroid and brassinolide biosynthesis pathways, with key metabolites such as 6-deoxotyphasterol upregulated and 4,4-dimethyl-5alpha-cholesta-8,14,24-trien-3beta-ol downregulated. Inhibitor treatments reduced enzyme activities, increased malondialdehyde accumulation, and suppressed growth and photosynthetic efficiency. Overall, the combined SA and MeJA treatment together with fungal inoculation was associated with the strongest promotion of growth and stress resistance in C. pilosula. This study reveals the metabolic reprogramming features of microbe-hormone interactions in medicinal plants and provides theoretical support for the quality cultivation of C. pilosula.