Searching for the root of ginseng’s replant disease

Carl Atkinson, research committee chair, Ontario Ginseng Growers’ Association.

Down below, underneath the mat of ginseng plants, is a whodunit mystery that’s slowly being unearthed. For all the success of the medicinal root, there is something in the soil that results in crop failure when ginseng is replanted in the same garden. In ginseng circles, it’s simply called replant disease. 

 

For Ontario’s 160 ginseng growers on the sand plains of Lake Erie, replant disease is a serious issue that threatens the long-term future of a $250 million industry.  Since the 1960s, the soil-borne disease has baffled ginseng growers. Basic research shows that several fungal plant pathogens cause cylindrocarpon root rot. Now that 8,000 acres are planted to ginseng, 2,500 of which are in mature production, the industry has pledged to manage its destiny. 

 

“It’s been a rallying cry,” says Carl Atkinson, chair, Ontario Ginseng Growers’ Association (OGGA) research committee. “We’re closer to solving the replant issue with government funding of $420,000 over the last five years. But the fact remains that sandy soils are finite in this area and we compete with vegetable crops. We can’t own every piece of land.”

 

So fierce is the competition for land that $800 per acre leasing costs are considered the norm. Ginseng is harvested once, after a three or four-year growth period under shading that replicates its natural forest habitat. Then new planting ground must be sought.

 

“Replant disease lasts at least 30 years,” explains Dr. Sean Westerveld, ginseng and herbs specialist, Ontario Ministry of Agriculture, Food and Rural Affairs, while pointing out that the disease does not affect any other subsequent crop.  “We don’t know why the disease is so severe in the second planting. This is not the normal pattern of a disease.”

 

Speculation is that the exudates of the ginseng root, the very medicinal components that are so healthy for humans, are actually contributing to disease in the second crop.

 

“There are a whole range of them,” says Westerveld. “These breakdown products are called ginsenosides.”

 

About 70 per cent of Westerveld’s time is spent in the ginseng industry, coordinating and monitoring a 25-person working group.  Thanks to Agriculture and Agri-Food Canada (AAFC) funding in the last five years, there is a multi-pronged approach to understanding the disease.   

 

Many university, government and industry experts have joined growers on a methodical approach. Soil testing has been the natural place to start a baseline of knowledge. A fungus called Ilyonectria mors-panacis is thought to be the culprit.  Dr. Mary Ruth McDonald, research program director for the University of Guelph’s plant department, is working on improving soil diagnostics for the fungus. Other researchers are working on next-generation sequencing to scan all fungi in the soil. 

 

“Remember there are tons of beneficial micro-organisms in the soil,” says Westerveld. “There is so much data that we look at groups of organisms and see how they shift over the time of a ginseng planting. The idea is to see if the exudates are affecting these (micro-organism) populations.” 

 

In another approach, private companies with expertise in biofumigation, fertilizer and pest control have conducted trials on grower plots. To date, the most promise is shown with mustard bio-fumigation and anaerobic disinfestation. 

 

“None of these are quick solutions,” admits Westerveld. “In my opinion, it will take another five years of research before any real progress is made.” 

 

If $2.8 million in federal funding is approved under the Canadian Agricultural Partnership, plans are to dedicate four faculty between the University of Western Ontario and University of Guelph to work on a remedy. That would be significant news, given that there were zero researchers committed to ginseng replant disease just five years ago.

 

None of this would be possible without growers on the ground. Ginseng is notoriously hard to grow in a laboratory and the soils of the Simcoe Research Station are too loamy, not sandy enough for real-life trials. About 15 per cent of the association’s growers participate in research, allowing summer students to come to their farms to take root and soil samples.

 

“We have a lot of involvement from growers,” points out Atkinson. “We have total buy-in from the ginseng community which includes growers, input providers and ginseng buyers.

 

Remi Van De Slyke, OGGA chair, agrees that the industry is on the right path with a robust team of experts. He returned November 13 from a trip to Shanghai, China, signing an agreement to partner with a pharmaceutical company for Ontario-grown ginseng. With so much future business on the line, he’s optimistic that the replant issue will be solved in the years to come.  “We will stay the course,” he concludes. 

Karen Davidson, editor of The Grower goes "Behind the Scenes" of this story and speaks with ginseng grower Carl Atkinson about the challenges of replant disease. Click here to listen.

Publish date: 
Friday, November 30, 2018

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