March 29, 2004

UCSC scientists investigate impact of genetically modified plants on wild relatives of major California crop

By Jennifer McNulty

As an environmental scientist, Deborah Letourneau believes policy decisions should be based on the best information available at the time.

That’s why she’s trying to fill an information gap with her latest research on genetically modified plants.

As insect-resistance is bred into major crops, Letourneau wonders how those crops’ wild relatives might be affected if they pick up the new traits.

“There’s been a lot of research on crop-to-crop movement,” said Letourneau, referring to the contamination of organic corn grown adjacent to genetically modified (GM) corn. “But we don’t know that much about the biology of wild crop relatives. If genes transferred, would it make them more weedy, more hardy, more invasive?”

To address these questions, Letourneau, a professor of environmental studies at UCSC, along with doctoral candidate Joy Hagen and Ingrid Parker, an associate professor of biology, have begun a three-year study to see what the consequences would be if GM genes transferred from Brassica plants through cross-pollination to their wild relatives.

Plants in the Brassica, or cole, family include many vegetable crops, such as broccoli, Brussels sprouts, cabbage, cauliflower, and kohlrabi, as well as common weeds like wild radish and wild mustard.

“Weed problems translate into economic problems for farmers,” said Letourneau, noting that 75 percent of cole crop production in the United States is concentrated on the Central Coast of California. Stubborn weeds require more herbicide applications, with accompanying higher labor costs and environmental impacts, she said, adding that highly invasive weeds can threaten native species on nonagricultural lands, too.

Letourneau is a leading authority on the genetic modification of plants. A member of the National Academy of Sciences’ 12-member panel investigating the environmental consequences of GM plants, she also coedited the 2002 book, Genetically Engineered Organisms: Assessing Environmental and Human Health Effects. Parker’s background is in applying mathematical models to ecological risk assessment for GM crops.

A growing number of crops are being genetically modified to increase insect resistance. More than 25 percent of corn grown in the United States has been genetically engineered to contain the toxin of the Bacillus thuringiensis (Bt) soil bacterium, which disrupts the digestive system of a caterpillar. Transgenic cotton and potatoes also produce Bt toxin.

Little is known about the role Bt-susceptible herbivores, including caterpillars, play in regulating the health and spread of wild crop relatives. In their research project, Letourneau and Hagen are protecting wild relatives from caterpillar damage to see what could happen if modified genes moved from Brassica crops to their wild relatives.

The simulation is necessary because the research is being conducted in open fields--not inside greenhouses--where risks of contamination by GM plants would be high, said Letourneau. To mimic an effect of gene transfer, the UCSC researchers are spraying Bt on wild radish and wild mustard growing adjacent to commercial cole crops, and they will use models to evaluate the subsequent fitness, weediness, and invasiveness of the weedy relatives, said Letourneau.

“We can’t use real transgenic crops, but we wanted to conduct this work where wild relatives live side-by-side with commercial crops,” said Letourneau. Research sites include the UCSC Farm and agricultural parcels adjacent to natural ecosystems from Wilder State Park to Elkhorn Slough Reserve.

Genetic links between crops and weeds are remarkably common, and cole crops are no exception, noted Parker. “In the past, the evolution of many weeds has been driven by genes coming from crops,” she said. “Now those genes will be specially engineered by humans.”

Research on consequences for wild relatives is overdue, said Letourneau, noting that field-testing of GM cole crops for California has been under way since 1999.
“This kind of research is important now, during the process of risk assessment, to know whether new modified crops should be deregulated or not,” she said. “There are a lot of Bt crops in the pipeline. Anything we can find out now can be used by regulators to make more informed decisions.”

Letourneau takes nothing for granted as the research gets under way. The project will use a large number of sample plants on varied research sites, and the experiments will be replicated over three years.

Hazards of GM corn, including allergenicity and contamination of adjacent fields, were identified during extensive testing that was required because it is a food.

Because similar tests are not required on nonfood plants, it’s harder to know what the hazards might be, and what the probability is that they’ll occur, said Letourneau. “It might be that transgene movement to wild relatives would be no problem at all,” she said. “If we don’t detect any problems or hazards, we’ll feel we’ve tried to provide the data needed for risk assessment.”

The three-year project, funded by a $335,000 grant from the U.S. Department of Agriculture, is something of a conquest for Letourneau.

“I’ve been trying since 1995 to get this research funded,” she said, referring to early studies of gene transfer that showed the likely crossing of traits from GM crops to wild relatives.

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