Re: Knapweed, an exotic plant killer

HOW AWFUL! 
I'm going to look for a picture of this monster.
Hope it hates heat.

---------- Original Message ----------------------------------
From: "Bonnie Holmes" <holmesbm@usit.net>
Reply-To: gardenchat@hort.net
Date:  Wed, 10 Sep 2003 09:18:53 -0700

>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]
>
>---------------------------------------------------------------------
>To sign-off this list, send email to majordomo@hort.net with the
>message text UNSUBSCRIBE GARDENCHAT
>
>

--
Pam Evans
Kemp TX/zone 8A



--

---------------------------------------------------------------------
To sign-off this list, send email to majordomo@hort.net with the
message text UNSUBSCRIBE GARDENCHAT
Other Mailing lists | Author Index | Date Index | Subject Index | Thread Index