Posted on 9-8-2002

GM Crops Pass Traits To Weeds

TUCSON, Ariz., Aug. 8 (AScribe Newswire) -- For the first time, researchers
have shown that a gene artificially inserted into crop plants to fend off
pests can migrate to weeds in a natural environment and make the weeds
stronger. Scientists studied genetically engineered sunflowers -- those
modified with a gene that produces a chemical toxic to certain insects --
to see what happened when these foreign genes, called transgenes, were
inadvertently passed along to weedy relatives. "This is the first example
of what might happen if a beneficial transgene accidentally spread to a
wild population and then proliferated in subsequent generations," said
Allison Snow, a study co-author and a professor of biology at Ohio State
University. "Many crops can exchange genes with nearby wild relatives," she
said. "But few commercially grown crops in this country are genetically
engineered. Of those that are, only canola and squash could cross with
weeds."

In the current study, the resulting hybrid sunflowers that contained the
transgene had 50 percent more seeds than control hybrids without the gene.
These plants also had far less insect damage, suggesting that that the
insecticidal gene was working by preventing insects from eating the plant.
"We were surprised that a single transgene could have such a big effect on
seed production," Snow said. The researchers also found that the addition
of this gene didn't harm the weeds' physical fitness, even when the
sunflowers were deprived of water and nutrients. "A plant with a transgene
may have to divert more energy to handle this new compound it's making,"
Snow said. "Doing so could reduce the plant's ability to reproduce. But
that certainly wasn't the case here." Snow conducted the study with
researchers from the University of Nebraska and Indiana University. The
team presented their findings August 8 at the annual Ecological Society of
America meeting in Tucson. The researchers crossbred cultivated sunflowers
that contained a Bt transgene -- a gene taken from the soil-dwelling
bacterium Bacillus thuringiensis that produces chemicals toxic to certain
insects -- with wild, non-Bt sunflowers. In this case, the Bt toxin
repelled moths and butterflies, whose larvae are prime sunflower predators.
The scientists focused on the second generation of wild sunflowers that
contained the transgene. The experimental populations were grown at two
sites -- an open, pasture-like area in Nebraska and an intensely cultivated
area in Colorado. The plants in Nebraska benefited more from the Bt
transgene than those in Colorado, most likely due to differences in insect
pressure, Snow said.

If a wild relative grows near a crop plant, chances are good that the two
will crossbreed. Such unions happen in more than 20 species in the United
States, including sunflowers, sorghum, carrots, radishes, rice and turf
grasses. But these crops don't yet contain insect-fighting transgenes in
their DNA. It's the plants that do contain transgenes that concern
researchers. "Many genetically-modified cultivated crops could potentially
crossbreed with weeds," Snow said. "Weeds are already hardy plants; the
addition of transgenes could just make them tougher. "While it's obvious
that a single gene can have a huge impact on plant reproduction in a
natural setting, there are still a lot of unknown effects, like whether or
not the weed could spread at a faster rate." Adding a transgene to a
plant's DNA could potentially weaken that plant's
ability to reproduce.

To test the effect of the transgene on the Bt sunflowers' physical fitness,
the researchers used three separate populations of wild transgenic
sunflowers in a greenhouse. One group was subject to drought; a second
group was deprived of nutrients; and a third group, which received adequate
water and nutrients, served as a control. The transgene didn't pose any
threat to any of the sunflower groups' fertility or growth. "There were no
costs at all to inheriting the transgene," Snow said. In order to keep the
sunflowers from spreading outside of the area of the field experiments, the
researchers removed all of the non-sterile plants that carried the Bt gene.
The researchers also collected seed heads from all of the remaining Bt
sunflowers before the seeds had a chance to fall to the ground. During the
two years following the study, the experimental plots and surrounding areas
were sprayed with herbicides meant to kill wild sunflower seedlings.
Although the researchers let the sunflowers grow in natural conditions for
this study, Bt sunflowers aren't currently sold in the United States.
"Their commercialization depends on securing approval from the U.S.
Department of Agriculture to grow Bt sunflowers, and if seed companies want
to market the plants," Snow said. She and her colleagues are continuing
their research and trying to understand if wild sunflowers with beneficial
transgenes could become troublesome weeds.

Snow conducted the study with Michael Reagon, a doctoral student at Ohio
State; Diana Pilson, a professor of biology, and Matthew Paulsen and Nick
Pleskac, all of the University of Nebraska; and Loren Rieseberg, a
professor of biology, and Diana Wolfe, both of Indiana University,
Bloomington. The research was supported by the U.S. Department of
Agriculture and seed manufacturers Pioneer Hi-Bred and Mycogen Seeds.

NOTE: This study on genetically modified sunflowers was funded in part by
Pioneer Hi-Bred and Mycogen Seeds, companies that supplied the sunflower
seeds for the study. None of the investigators has served as a consultant
for either seed company. Dr. Loren Rieseberg of Indiana University has
received an additional research grant from Pioneer Hi-Bred. None of the
other scientists have financial ties beyond the scope of this study.