Yellow peas: a case of mistaken identity

For those outside the agricultural industry, it may come as a surprise to learn that Canada is the world's largest producer and exporter of peas. Canada accounts for close to one-third of world pea production and well over half of world pea exports.Footnote 1 Exports of yellow peas alone to just one country, India, are worth an average of almost $400 million a year.Footnote 2

Microscopic views of the quarantine pest D. dispaci (left) and D. weischeri (right). These nematodes are about the size of a human hair in diameter.
(Photo credit: AAFC)

For more than a decade, Canada's yellow pea exports to India have been threatened by a microscopic worm—or nematode—that attacks a whole range of important food crops. This stem and bulb nematode is named Ditylenchus dipsaci, or just D. dipsaci. Because it can do so much damage to a variety of crops, D. dipsaci is considered a "quarantine pest" in many places in the world—countries will not accept imports of agricultural commodities or plants that are infested with the nematode.

Costly pest identified in Canadian exports

Since 2004, when D. dipsaci was detected in Canadian yellow peas, India has required every shipment of yellow peas from Canada to be checked for and certified free the nematode. If the pest was found, the ship carrying the peas would have to divert to a third country to be fumigated to destroy the nematode before it could deliver its cargo to India. The cost to shippers could reach into the hundreds-of-thousands of dollars per loadFootnote 3.

A series of scientific developments in recent years has eased the situation for Canadian exporters of yellow peas to India, beginning with the identification by a Russian scientist in 2010 of a species of nematode very similar to D. dispaci. This one, found on Canada thistle—a common weed—was named D. weischeri.

Curious about this new finding, a professor at the University of Manitoba tested some samples of nematodes from yellow peas and identified them as the species described by the Russian scientist. The professor shared the samples with Agriculture and Agri-Food Canada (AAFC) Research Scientist Dr. Qing Yu, an expert in nematodes. Using both physical examination and genetic testing, Dr. Yu confirmed the nematodes were indeed D. weischeri.

Genomics provides conclusive proof

Dr. Yu says a lot of nematodes look alike and misidentification does happen. "In this case, looking through a microscope, it is very difficult to tell these two apart," says Dr. Yu, "However, when we apply a molecular test to compare the genetic characteristics of the two species, the difference is very clear."

Along with the differences in their genetic sequence revealed by the molecular testing, D. dispaci and D. weischeri differ in another, very significant way: D. weischeri is not a quarantined pest nor is it a known pest of peas.

Following this discovery, DNA-based testing was carried out on samples of Canadian yellow peas dating back to the first detection of D. dispaci in 2004. In every case, the nematode thought to be D. dispaci was in fact D. weischeri.

Dr. Yu says the Government of Canada's Genomics Research and Development Initiative (GRDI) played a key role. "If we did not have access to the knowledge and resources developed through earlier projects funded by the GRDI," says Dr. Yu, "We might not have been to obtain such conclusive evidence."

Improved access to key market

At the Canadian Food Inspection Agency (CFIA), Executive Director of the Plant Health Science Directorate Cameron Duff says genetic testing is now used to demonstrate that yellow peas from Canada are free of D. dispaci. "The D. weischeri has been identified in some shipments," says Mr. Duff. "In the past, they would have been considered as D. dispaci and the shipments would have been subject to the expense of diversion and fumigation before they could be unloaded in India."

To date, not a single instance of D. dispaci has been identified in Canadian yellow peas.

"This strengthens the belief that yellow peas are not carriers of this quarantine nematode," says Mr. Duff. "Based on this evidence, we are hopeful that India will soon agree to modify the requirements for nematode testing on our yellow peas."

Science helping industry

Gord Kurbis, Director of Market Access and Trade Policy at Pulse Canada—which represents growers of peas and other pulse crops such as lentils, beans and chickpeas—says this has been a long and costly issue for Canadian producers. "India is our most important market for yellow peas. We need predictability and stability in our agricultural trade," says Mr. Kurbis. "The issue is not fully resolved, but there is no question this new development in nematode diagnostics is a great example of how applied science can help to improve business and profitability for growers and exporters."


Footnote 1

Canadian Agri-Food Trade Alliance, Pulses

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Footnote 2

Pulse Canada, interview with Gord Kurbis, 11 March 2014

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Footnote 3

Gordon Bacon, CEO, Pulse Canada, evidence to Standing Committee on International Trade, 27 February 2013

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