Saving Dutch Elms From
Disease With A Vaccine
Elms grow up to 40 metres and some live as long as 400 years.
They've been around for 40 million years. Graceful and majestic, elms can be found all over the world, their crowns providing shade and coolness along boulevards and streets of cities. They also provide clean air and protection from UV radiation. But these tall, leafy trees are under attack - in England, the United States, and now Canada.
The enemy is a fungus that invades the tree, clogging its vascular system - the vessels that carry water - and causing the leaves to wilt. After a season or two, the tree is left dry and dead. Since Dutch elm disease first arrived in this country in Quebec during the 1940s aboard lumber shipments, it has wiped out as many as 2 million elms. Today, there are only about 700,000 elms as shade trees in the country. But now the disease front has reached the elm populations of Saskatchewan and threatens those of Alberta a situation that's worrying both private citizens and governments alike.
Dutch elm disease emerged in Holland shortly after World War I, and quickly made its way over to Great Britain (1927), the United States (1930), and then to Canada (1945). It causes elms to wilt and die of thirst. "In the prairie provinces," writes Dr. Martin Hubbes, a forest pathologist at the University of Toronto, in The Forestry Chronicle, "elms constitute the majority of shade trees in cities and villages. No other tree is better suited than the elm to withstand the harsh winter climate and urban environmental stresses in these regions, with its high winds, extreme temperatures and road salt."
So the residents and local and provincial governments are fighting back - with a vaccine that boosts the immune systems of the elms.
The tiny (although it doesn't look so tiny here) bark beetle carries the fungus on its back from tree to tree. To kill trees, the fungus that causes Dutch elm disease needs a way to get around. The culprit: the bark beetle. This tiny critter tunnels under the bark to eat and lays eggs, all the while carrying the fungus on its back, spreading it from tree to tree.
While past efforts have focused on insecticide to kill the carriers of the fungus, or fungicide to wipe out the fungus itself, a group at the University of Toronto are working on a vaccine to prevent the disease from infecting the trees. It believes that trees have natural defences against disease a kind of immune system just like us humans.
Hubbes group has been "vaccinating" elms in Winnipeg and in Ontario and then injecting them with Dutch elm disease to see if they survive. The vaccine is inside this pellet that looks like a cigarette filter. "You can eat it, your cat eat it," says Hubbes, who developed the vaccine. "I have eaten it many times, so I am probably resistant against Dutch elm disease," he jokes.
Made from the fungus that causes the disease itself (Ophistoma ulmi), the active ingredient in the vaccine is something called glycoprotein.
Here's Hubbes' theory: Inside the tree, the glycoprotein activates cells around water-conducting vessels, putting them in a state of alert. When the fungus attacks, the cells go into action, making materials that thicken the vessel walls. This traps the fungus so it can't spread to the rest of the tree.
How the vaccine works
By "vaccinating" elms, Hubbes believes the trees will develop a resistance to the disease.
And their field trials are showing that it's working.
"The results have been very encouraging," says Paul Oliver, of ArborScience Inc. in Toronto, the company that's planning to market the vaccine. "Our target range is 80 to 85 per cent protection [against Dutch elm disease]. The results so far are above and below that target. We're now analyzing each tree."
Now in the middle of its third year of field trials, this year's results will allow the team to figure out exactly how the vaccine works. Understanding how factors such as the genetic background of a particular tree, its health, and the weather affect the vaccine's efficacy, will allow the team to refine the vaccine.
While it's not practical to inject hundreds of thousands of trees in forests, the team hopes the vaccine can at least help cherished urban elms. ArborScience Inc. hopes to have at least a limited release of the vaccine next spring.
For more on this story, try these links: <http://www.arborscience.comArborScience Inc. < Dutch Elm Disease Prevention in Alberta