Effects of Fusarium solani and F. oxysporum Infection on the Metabolism of Ginsenosides in American Ginseng Roots

American ginseng (Panax quinquefolius L.) is a highly valuable herb widely used for medicinal treatments. Its pharmacologically important compounds are the ginsenosides, which are secondary metabolites in American ginseng root. The concentrations of ginsenoside in roots can be changed by fungal infection, but it is unclear what specific root tissues are impacted and whether the change is systemic. In this study, American ginseng roots were inoculated with two fungal pathogens (Fusarium solani or F. oxysporum) and the levels of six ginsenosides (Rb(1), Rb(2), Rc, Rd, Re, and Rg(1)) were then measured in the phloem and xylem around the discolored lesions and adjacent healthy areas of the root. Results indicated that the growth of Fusarium spp. was strictly limited to phloem, and correspondingly the ginsenoside concentration was only altered in this infected phloem. The concentration of Rg(1), Rd, and Rc significantly changed in phloem tissues where F. solani was inoculated, while only Rg(1) and Rd changed significantly after F. oxysporum inoculation. However, no changes of any ginsenoside occurred in either xylem or phloem tissue adjacent to the inoculation point. In addition, when two Fusarium spp. were grown on ginsenoside-amended Czapek medium, the majority of ginsenosides were depleted. Therefore, pathogenic Fusarium spp. may reduce ginsenoside levels by consuming them.