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Home > Elms in Winnipeg March 2000 - Part 4

 Last Update 02/04/07  

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Hubbes began studying Dutch elm disease in 1968 and quickly became fascinated by the many ways trees react to the threat of infection. When bark beetles laden with fungal spores burrow their way under the craggy bark of an elm, the tree responds to the invasion with what Hubbes describes as a "cascade of defensive reactions," including the production of compounds called mansonones that help ward off fungal infestation. He and his colleagues have succeeded in isolating from the fungus a glycoprotein "elicitor" that tricks the tree into mounting its protective cascade.


"What the tree tries to do," explains Hubbes, "is to wall the fungus off in a confined space so that it cannot further invade the vascular system. The trees actually shut down the cell walls and surround the fungus with an inert tissue so that the fungus cannot penetrate the tree further."


Once the defences are elicited and the fungus is isolated, the host tree is then primed with antifungal mansonones (related to a group of substances called sesquiterpine quinones) that destroy the fungus. "They kill by attacking mitochondria, the energy powerhouses of the fungus," Hubbes told New Scientist magazine last year after news of the discoveries began to filter out. Since then, there's been a surge of international attention. 
"It was incredible how a much renewed interest flared up around the world," Hubbes says now in his Toronto lab. A plant pathologist who seems torn between modesty ("We didn't want a lot of propaganda because we like to work in a quiet atmosphere") and bubbling enthusiasm for saving trees, he can't help letting the enthusiasm surface. "We're getting inquiries from all over the world," he says, "the U.S., Australia, New Zealand, Europe." Everyone, its seems, wants their elms back.


Hubbes and his colleagues are busy conducting field tests in Winnipeg, Toronto, and several other places in Ontario, treating trees with the elicitor and then exposing them to high dosages of Ophiostoma ulmi spores "to see how good the stuff is." They have also begun to treat elms in Saskatchewan and Alberta but have carefully avoided introducing any fungus to vulnerable stands of elms there. Results are already encouraging. In one trial, all the trees in the control group died when exposed to the fungus, whereas only one in 33 vaccinated trees succumbed. 


Hubbes agrees that Winnipeg has a natural advantage because of its genetically diverse elm population. But here again, Canada's richest urban elm forest presents paradoxical problems inherent in any effort to intervene with a complex ecological system. 


"For our treatment, wide diversity within the species is not so good," Hubbes says. "If I could just treat clones of a single variant, it would be so much easier for me because one cloned tree would react the same as a thousand others. But where there's high diversity, some trees do very well, while others require more conditioning."


Another variable is the influence of the tree's environment. A handsome old elm standing alone on a rural fence row may survive because it's being nourished by good agricultural soils. "When you plant them in a city where you have a dreadful environment," says Hubbes, "they might not react the same way. That's why we have to understand the defence mechanisms. Once we do that, then I think we'll have solved the problem."


Hubbes admits that even after 30 years of study, there's still much to learn about the immune systems of Ulmus americana, particularly in a forest ecology as complex as that of Winnipeg. But he is in no doubt about the prairie city's role in sustaining the work that finally seems to be bearing fruit. "If Winnipeg hadn't supported us," he says, "I would have given up a long time ago." Most people, including Ottawa politicians and officials who have stopped supporting Dutch elm disease research, still hear the word elm and immediately think of those skeletal remains that dot the rural landscape in eastern Canada. Hubbes keeps getting advice from people who say, "The elm? Don't bother. It's dead, forget about it." 


But it's not dead in Winnipeg. "I grew up in Montreal when all of the elms died and the city didn't act to save them," recalls Glen Murray. "I remember very vividly the trees disappearing in my neighbourhood. Here in Winnipeg, people have a real attachment to the trees. It's part of our identity as a city." And thanks to officials like Mike Allen and citizen activists like Judy Werier, tree huggers whose stubbornness was perhaps inherited from the women in the cloth coats who defended the Wolseley elm, eastern cities may one day rejoice again under their own restorative canopies of stately elms. 

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Jamie Swift is a writer and broadcaster living in Kingston, Ontario. His most recent book, Wheel of Fortune, was published in 1995. He is also the author of Cut and Run, a lament for the mismanagement of Canadian forests.

 


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