Influence of Ginsenosides on the Pathogenicity of Ilyonectria

Commercial cultivation of American ginseng (Panax quinquefolius L.) suffers from ginseng replant disease (GRD) when planted in a former ginseng garden. GRD typically manifests as a severe root-rot due to fungus Ilyonectria mors-panacis. Ginsenosides released to the soil by ginseng are thought to contribute to GRD but, to be effective, ginsenosides need to be present in the soil. Using soils collected from commercial ginseng gardens, I show that ginsenosides accumulate for the first three and a half years of cultivation but decline in the fourth year. They are largely gone within one-year post- harvest, suggesting that they are not direct contributors during GRD. Instead, I revealed that Ilyonectria spp., specifically I. rufa, increase in virulence on ginseng roots when pre-exposed to ginsenosides in vitro, suggesting ginsenosides may contribute to establishing the GRD state. Additionally, while various Ilyonectria isolates were able to metabolize select ginsenosides, this did not correlate with virulence.