Paraphoma chrysanthemicola Affects the Carbohydrate and Lobetyolin Metabolism Regulated by Salicylic Acid in the Soilless Cultivation of Codonopsis pilosula

Paraphoma chrysanthemicola, an endophytic fungus isolated from the roots of Codonopsis pilosula, influences salicylic acid (SA) levels. The interaction mechanism between SA and P. chrysanthemicola within C. pilosula remains elusive. To elucidate this, an experiment was conducted with four treatments: sterile water (CK), P. chrysanthemicola (FG), SA, and a combination of P. chrysanthemicola with salicylic acid (FG+SA). Results indicated that P. chrysanthemicola enhanced plant growth and counteracted the growth inhibition caused by exogenous SA. Physiological analysis showed that P. chrysanthemicola reduced carbohydrate content and enzymatic activity in C. pilosula without affecting total chlorophyll concentration and attenuated the increase in these parameters induced by exogenous SA. Secondary metabolite profiling showed a decrease in soluble proteins and lobetyolin levels in the FG group, whereas SA treatment led to an increase. Both P. chrysanthemicola and SA treatments decreased antioxidase-like activity. Notably, the FG group exhibited higher nitric oxide (NO) levels, and the SA group exhibited higher hydrogen peroxide (H2O2) levels in the stems. This study elucidated the intricate context of the symbiotic dynamics between the plant species P. chrysanthemicola and C. pilosula, where an antagonistic interaction involving salicylic acid was prominently observed. This antagonism was observed in the equilibrium between carbohydrate metabolism and secondary metabolism. This equilibrium had the potential to engage reactive oxygen species (ROS) and nitric oxide (NO).