[APWG] spotted knapweed article NYTimes

[MALawler at aol.com]

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
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.plantconservation.org/pipermail/apwg_lists.plantconservation.org/attachments/20030909/a66c7002/attachment.html>