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Engineered Crops Resist Herbicides, Reduce Use Of Toxic Weed-Killers

October 20, 1988

LOS ANGELES (AP) _ Scientists have devised a way to make crops survive a biodegradable weed- killer, a method they said may save farmers money, boost crop yields and protect the environment from heavy use of toxic herbicides.

″The potential benefit is mind-boggling,″ Terry Medley of the U.S. Department of Agriculture said of the study by Calgene, of Davis, Calif., and similar efforts by Monsanto Co. and E.I. du Pont de Nemours & Co. to develop herbicide-resistant crops.

Such crops ″will save the farmer money, and give the farmer the ability to spray less herbicide and use an environmentally safe herbicide,″ said David M. Stalker, author of a study published in Friday’s issue of the journal Science.

Stalker and other molecular biologists at Calgene said they successfully removed a gene, or hereditary instruction, from soil bacteria and inserted it into tobacco plants. The gene makes the plants produce an enzyme that destroys the biodegradable herbicide bromoxynil, said Roger Salquist, Calgene’s president and chief executive officer.

The plants survived without damage when sprayed with eight times the dose of bromoxynil that normally kills them, said the study by Stalker, Kevin McBride and Lorraine Malyj.

Calgene scientists also engineered tomato and cotton plants to resist the weed-killer, Salquist said.

Bromoxynil-resistant crops should let growers reduce their chemical costs because bromoxynil belongs to a new class of weed-killers that are used in relatively low doses and don’t persist in the environment, said Salquist, Stalker and Jodie S. Holt, a plant physiologist at the University of California, Riverside.

″Those are chemicals we want to keep on the market, as opposed to using older, more toxic and more persistent chemicals,″ Holt said.

″Something that would allow use of this new generation of safer herbicides is important,″ said Medley, the USDA’s director of biotechnology and environmental coordination. ″The benefit to society, not just to the farmer, can be great.″

Salquist said bromoxynil now is used only to kill weeds in fields of crops that resist it naturally, including corn, wheat and barley.

Calgene’s study was funded by Rhone Poulenc Agrochemie, the French firm that sells bromoxynil under the name Buctril. Salquist said Calgene and the French company obviously want to make money selling seeds for Buctril- resistant crops and Buctril itself, but farmers and the environment also will benefit.

Some genetically engineered plants produce fewer seeds. But Salquist said field tests of Calgene’s altered tomatoes showed no damage to their yields.

Genetically engineered crops tolerate bromoxynil well, so they should have higher yields than natural crops that are sprayed with other herbicides that slightly stunt crop growth while killing weeds, Stalker said.

The Calgene-owned Stoneville Pedigreed Seed Co. of Mississippi, the nation’s second leading producer of cotton seeds, plans to market bromoxynil- resistant cotton seeds by 1992, Salquist said.

He estimated use of the seeds and bromoxynil should reduce the $382 per acre cost of growing cotton in the Mississippi Delta by $46 to $57, including reduced herbicide costs and increased crop yields.

One theoretical concern is whether bromoxynil’s breakdown products could be toxic to humans who eat plants sprayed with the herbicide. Holt said those chemicals occur naturally in corn, wheat, rye and oats - which have natural resistance to the herbicide - and are not known to be toxic.

Stalker said he expects ongoing studies will show that bromoxynil is completely broken down in the resistant crops, leaving no residue.

Another concern is that weeds might become resistant to bromoxynil, either by crossbreeding with the genetically engineered crops or because natural selection will favor survival of mutant weeds resistant to the herbicide while vulnerable weeds die.

Medley said the USDA found no risk of herbicide-resistance being transferred sexually to weeds from tomatoes, cotton and tobacco. Holt said she agreed with Stalker that because bromoxynil breaks down in a couple weeks, development of mutant, bromoxynil-resistant weed populations are less likely than with longer-lived herbicides.

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