Electronic Thesis and Dissertation Repository

Thesis Format

Monograph

Degree

Master of Science

Program

Biology

Supervisor

Bernards, Mark A

Abstract

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.

Summary for Lay Audience

Ginseng is a valuable plant grown for its use in Traditional Chinese Medicine (TCM). American ginseng is grown commercially in North America and yields more than $100 million in sales each year. Ginseng growers face a big challenge known as ginseng replant disease (GRD). GRD is characterized by root rot disease caused by the fungus Ilyonectria mors-panacis when ginseng are cultivated in soil previously used for growing the crop. GRD is thought to be helped by ginsenosides, the chemical compounds produced by ginseng that give the roots their value in TCM. This is because ginsenosides can increase the growth of the fungus Ilyonectria mors-panacis. To have an effect on Ilyonectria mors-panacis growth in a ginseng garden, ginsenosides have to be present in the soil. In my thesis work, I found that ginsenosides accumulate in ginseng soils over the first three and a half years of cultivation. Then the levels drop by the time of harvest. Ginsenoside levels drop further after harvest and are barely present in the soil a year later. Since ginsenosides do not exist in the soil for a long time, they cannot be a direct cause of GRD. To understand how ginsenosides relate to GRD, I next studied how Ilyonectria mors-panacis and related species change when they were exposed to ginsenosides in our lab. I found that a species similar to Ilyonectria mors-panacis, known as Ilyonectria rufa, became more harmful to ginseng after it was exposed to ginsenosides. My research suggests that some Ilyonectria fungi may become more harmful when exposed to ginsenosides in the soil while ginseng is being grown. This makes them more able to infect ginseng the next time it is planted in the same garden.

Creative Commons License

Creative Commons Attribution-Noncommercial 4.0 License
This work is licensed under a Creative Commons Attribution-Noncommercial 4.0 License

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