Changes in ginsenosides and soil biodiversity related to management of ginseng replant disease****

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It is well known by growers that after one crop, it is not possible to plant ginseng in the same gardens. Frequently, the new crop will quickly succumb to root rot disease colloquially referred to as replant disease. The persistence of replant disease is measured in decades. Due to replant disease, suitable sandy soils on which ginseng has not been grown previously are becoming scarce. It is estimated that there will not be any more suitable land for ginseng production in Ontario in the next 20 to 30 years. In the meantime, travel to fields up to an hour from their home farms and decreased yields from moving to increasingly marginal land costs the industry an estimated $40 million/yr. Replant disease is not as simple as the persistence of specific disease-causing organisms in former ginseng gardens. Instead, there is growing evidence that critical changes in both soil chemistry and microorganism biology in ginseng gardens occur post-harvest and render ginseng gardens unsuitable for a second crop of ginseng. Ginsenosides are chemical compounds made by ginseng that provide the plant with some of its medicinal properties. These compounds are known to be released into the soil, and can be modified by soil-borne microorganisms. We hypothesize that ginsenosides are biotransformed by resident soil microbes, creating a soil environment in which highly virulent forms of the organisms that comprise the replant disease complex can establish. To address this hypothesis in the present proposal we will establish the relationship between ginsenosides and the microbiome in field soil, during cultivation of ginseng in a new garden, as well as in a recently harvested garden. We will also monitor the impact of specific soil treatments on the soil microbiome and ginsenosides in the field and the greenhouse. We will identify key organisms and types of ginsenosides associated with increasing levels of root rot during replant disease and establish molecular markers for their routine identification in soil samples (e.g., to determine whether a field is at risk for replant disease). Finally, we propose to identify unique gene features of identified organisms and use them as potential targets for selective management intervention.****************