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- Elms grow up to 40 metres and some live as long as 400
years.
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- 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.
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- 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.
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- 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."
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- So the residents and local and provincial governments
are fighting back - with a vaccine that boosts the immune systems of the
elms.
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- 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.
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- 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.
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- 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.
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- Made from the fungus that causes the disease itself (Ophistoma
ulmi), the active ingredient in the vaccine is something called glycoprotein.
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- 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.
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- How the vaccine works
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- By "vaccinating" elms, Hubbes believes the
trees will develop a resistance to the disease.
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- And their field trials are showing that it's working.
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- "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."
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- 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.
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- 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.
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- For more on this story, try these links: <http://www.arborscience.comArborScience
Inc. < http://www.agric.gov.ab.ca/pests/diseases/ded/index.html Dutch
Elm Disease Prevention in Alberta
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