Canadian test for pine wood nematode included in new international protocol

The forest industry has always been a mainstay of the Canadian economy. Today, the sector accounts for more than $30 billion a year in exports,Footnote 1 from logs and lumber to plywood and paper products. Some $8 billion a year in softwood lumber alone—pine, spruce and other coniferous woods—is exported to countries around the world.

These exports are an essential part of Canada's prosperity, but access to international markets is not guaranteed. Virtually all countries, including Canada, regulate wood imports to ensure potentially damaging invasive species are not being imported along with the wood. If a so-called quarantine pest is found, the shipment may be turned away and future shipments put in jeopardy.

In 1993, for example, the European Union banned most softwood lumber imports from Canada after finding the pine wood nematode in a shipment. Known as PWN, the microscopic worm—less than a millimetre in length—causes a disease called pine wilt that can kill a mature tree in a matter of weeks. In the years immediately after the ban was imposed, Canadian softwood sawn wood exports to western Europe, worth up to $700 million a year at the time,Footnote 2 fell by as much as 80 percent.

Not wanted dead or alive

As part of the response to the EU trade action, Canadian lumber companies began using heat treatment and other phytosanitary measures to eliminate PWN in their products. Although only living organisms are regulated, some countries may reject lumber with any trace of PWN, even if the nematodes they find are dead.

There is also a risk of misidentification. Dr. Isabel Leal—a Research Scientist with Natural Resources Canada's Canadian Forest Service—explains that there is another, related species of nematode that is extremely similar to PWN, but that does not cause pine wilt. "Finding someone with the morphological expertise needed to tell which is which can be difficult and time-consuming—and a mistake in identification can have significant economic consequences."

DNA vs. RNA

Looking at an organism's DNA provides is a very accurate means of identification, but in the case of PWN, more than accurate identification was needed. "You can obtain DNA from something that's been dead for a long time ," says Dr. Leal. "We wanted a test that would tell us whether there were any living PWN in the wood."

That meant looking not only for the nematode's DNA, but also a second distinguishing molecular product: ribonucleic acid, or RNA. "RNA is an appropriate indicator of viability, as it is a transient molecule—it is present in living cells, but degrades very quickly after an organism dies," says Dr. Leal. "So, even if we find its DNA—indicating the presence of PWN—if we don't also find its RNA, we know the organism is no longer living, and thus does not pose a threat."

GRDI funding key to success

Pine wilt disease—caused by the pine wood nematode—can rapidly kill a mature tree. (Photo: NRCan-CFS)

With funding from the Government of Canada's Genomics Research and Development Initiative (GRDI) and the Canadian Food Inspection Agency (CFIA), Dr. Leal had the resources to assemble a team of researchers and the tools needed to develop a molecular test that would identify both DNA and RNA from the nematode.

"There was a lot of work and experimentation involved in finding the right combination of chemicals and the best method to identify RNA  specifically from PWN and nothing else," says Dr. Leal. "In the end, we managed to find a way to do it." Along with accuracy, the test is also less labour-intensive than the previous method of finding living PWN in wood, so it is less expensive and, instead of several days, this test can be completed in a few hours.

Protecting exports, testing efficacy of wood treatments

The test developed by Dr. Leal—with her collaborators at both CFIA and Forest Product Innovations— gives Canadian exporters a fast and cost-effective way to make sure their phytosanitary processes are effective in eliminating PWN from their wood products. And it helps to protect Canada's export markets by assuring other countries they can import wood from Canada without fear it will lead to PWN infesting their forests.

The International Plant Protection Convention, a United Nations organization dedicated to protecting the world's plant resources from pests, has adopted a new standard diagnostic protocol for pine wood nematode, that includes the RNA test developed by Dr. Leal and her colleagues.

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