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Re: Knapweek, an exotic plant killer


Bonnie,
thanks for alerting us.  VERY interesting article.  I'm one of those lazy 
gardeners, who might not get around to weeding often - though I have 
comparitively few weeds because I have too many plants jammed on to this lot.  
But I do know others who are also lazy.  Reading what damage Knapweed 
(Centaurea maculosa) can do and so quickly, should put us all on our toes!
Kitty
> Thought you might find this interesting since it can kill other garden plants.
> September 9, 2003
> Forensic Botanists Find the Lethal Weapon of a Killer Weed
> By CAROL KAESUK YOON
> or over a century, spotted knapweed has been a growing scourge on the
> North American landscape, spreading across millions of acres of
> prairies, hillsides, roadsides and rangeland  pretty much anywhere it
> can get a root in the dirt. Everywhere it spreads, it replaces native
> grasses and other plant species to the consternation of conservationists
> as well as ranchers, whose cows refuse to eat it.
> 
> The weed, which sprouts pink and purple flowers and can grow a spindly
> three feet tall, is a European import, thought to have been introduced
> in North America as a contaminant in crop seeds or in dirt used as
> ship's ballast and then dumped. But scientists have long been baffled by
> the plant's appalling effectiveness at driving out other plants.
> 
> Now in the current issue of the journal Science, researchers say they
> have found spotted knapweed's deadly secret: a potent and previously
> unknown poison that it releases through its roots into the soil to kill
> off neighboring plants. By eliminating its neighbors, the weed can
> appropriate all the water and nutrients that the other plants would have
> taken, and it has plenty of new space to spread out in.
> 
> Dr. Jorge M. Vivanco, a plant biologist at Colorado State University and
> an author of the study, says the toxin acts so quickly that within 10
> seconds of contact the neighboring plants' roots begin producing
> chemicals that set off a cascade of events that will ultimately kill
> their own cells.
> 
> "In one hour the roots die," he said. "The whole plant dies in a matter
> of days." The substance is such an effective herbicide that, Dr. Vivanco
> said, his university had already taken out a patent on it.
> 
> Scientists often assume that invasive exotic species are able to thrive
> in new environments because they have escaped from their predators and
> other enemies at home. But scientists say the new study suggests that
> such troublesome imports may also succeed by using potent but
> unrecognized methods, like chemical warfare.
> 
> "This is a really nice demonstration that other factors come into play,"
> said Dr. Sarah Reichard, an invasion biologist at the University of
> Washington. "This paper shows that the interactions can be very subtle,
> things happening below ground that we really haven't had any knowledge
> about."
> 
> The notion that plants use poisons to suppress or kill their neighbors 
> a phenomenon known as allelopathy  has been around for decades. But
> until now, few scientists have had much use for it.
> 
> "People have been rather dismissive of the whole subject," said Dr.
> Alastair Fitter, an ecologist at the University of York who was not
> involved in the study.
> 
> Part of the problem was that much of the earliest work was poorly done,
> he said in a telephone interview. But as Dr. Fitter wrote in an
> accompanying commentary in Science, he believes the new study is so
> convincing that it will "now place allelopathy firmly back on center
> stage."
> 
> The researchers found that the roots of the spotted knapweed released
> two forms of a chemical known as catechin (pronounced KAT-uh-kin)
> identical in all respects except that their molecular structures were
> mirror images of each other.
> 
> One form, known as +catechin, is also found in green tea and was already
> known as an antioxidant, able to neutralize the harmful molecules called
> reactive oxygen species that are thought to speed the aging process.
> 
> The toxin turned out to be the second form, -catechin, which had
> essentially the opposite effect of its mirror image. It induced the
> production of harmful reactive oxygen species in neighboring plant
> roots, setting off the process that led to cell death.
> 
> The finding helps explain the failure of many efforts to fight the
> onslaught of spotted knapweed by burning it and then seeding the area
> with desired plants.
> 
> "What they've seen is that 99 percent of the seeds died, and now we know
> why," said Dr. Vivanco. With -catechin soaked into the soil, he said,
> susceptible seeds have no chance of making it.
> 
> But even though the poison is very powerful, it remained unknown to researchers 
> because everything was happening below ground.
> "One plant arrives in a field where there are a lot of native plants,"
> Dr. Vivanco said. "The next year you see not one, but actually a patch
> of spotted knapweed where the natives were. And if there are still
> native plants near it, they don't look so healthy."
> 
> Around Missoula, Mont., home of the University of Montana, for example, a 
> diversity of native species once bloomed.
> Now after several decades of this subtle underground warfare, the hills
> have become a vast monoculture of spotted knapweed, Dr. Vivanco said, as
> have millions of acres in that particularly hard-hit state.
> 
> The scientists found that the grasses that grow alongside spotted
> knapweed in Europe are much better able to resist its toxins than native
> North American grasses. Scientists say this suggests that the European
> grasses have evolved a resistance to this potent toxin, one that North
> American grasses lack.
> 
> Since spotted knapweed landed in North America, a century or so ago, it
> has spread to nearly every state and has caused a variety of problems.
> 
> Eric Lane, the state weed coordinator for Colorado, said the loss of
> native plant species curtailed the food supply not only for cattle but
> for wild species like elk, many birds and insects. In some states, he
> said, the spread of spotted knapweed is so severe that elk herds have
> altered migration pathways to avoid vast inedible swaths of it.
> 
> The weed has also led to erosion because it does not hold soil as well as native 
> grasses.
> In the search for solutions to this green plague, researchers were
> excited to discover that the plant Arabidopsis thaliana, whose entire
> genome has already been sequenced, is susceptible to -catechin. As a
> result, they can see in detail how a plant's genome reacts when its
> roots are hit with the toxin.
> 
> The scientists found 10 genes that appear to shift into high gear
> immediately. Scientists say they hope that by identifying what those
> genes are doing, presumably mounting the beginnings of a defense, they
> can genetically engineer plants that can more effectively resist the
> spotted knapweed's attacks.
> 
> Researchers are also testing to see what native plants are resistant to
> the -catechin. They hope to develop a list of species that can be used
> to revegetate an area after spotted knapweed has been burned.
> 
> So far, the researchers have found no native plants that can withstand the 
> poison.
> 
> 
> Copyright 2003 The New York Times Company
> 
> Bonnie Zone 6+ ETN
> 
> [demime 1.01d removed an attachment of type image/gif which had a name of f.gif]
> 
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