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Prickly lettuce: A lemon or lemonade?

Scientists are hoping to turn a lemon into lemonade by extracting the mechanism that makes the weed also called wild lettuce resistant to sulfonyl urea herbicide and put it into commercial lettuce varieties.

Steve Fennimore, University of California weed specialist stationed in Salinas, Calif., told the California Weed Science Society recently at its annual meeting in Santa Barbara, that California lettuce grower are walking a tight rope.

There have been virtually no new herbicides developed for lettuce growers who now depend on products developed decades ago. They still are effective, but how long they remain so and on the market in this rarified environmental environment may be tenuous.

There are proven, genetically modified, herbicide-tolerant commercial lettuce varieties on the shelf, ready for use. However, lettuce growers are leaving them there because they do not want to limit their marketing options. Countries like Japan and the European Union will not accept genetically modified crops.

When a Salinas Valley or desert winter lettuce grower plants a field, he wants as many market options as possible at harvesttime. GMO-lettuce would limit those markets, according to Fennimore.

Shelved programs

Growers are so opposed to biotechnology that the major seed companies developing the Roundup-resistant lettuces have shelved biotechnology programs for now.

However, Fennimore said that does not preclude lettuce varieties from being developed that are resistant to herbicides using conventional breeding to achieve that.

The precedent has been set with the recent introduction of herbicide-resistant Clearfield rice, soybeans, canola and other crops. These crops can be sprayed with a class of herbicides that will not harm the crop, but will kill the weeds. This was done without using biotechnology.

"Plant breeders have developed crops resistant to diseases: why not develop crops resistant to herbicides using conventional breeding," he said.

That is exactly what plant pathologists did at the University of Idaho.

Unfortunately for farmers in the Pacific Northwest, prickly lettuce has become resistant to sulfonyl urea herbicides. However, University of Idaho scientists have successfully crossed herbicide-resistant prickly lettuce with commercial lettuce.

Beiguin Mou, a new USDA-ARS lettuce breeder based in Salinas, now has that germplasm and he and Fennimore are working to develop commercial varieties for California and Arizona lettuce growers.

It is becoming imperative that producers uncover new weed control options, points out Fennimore. "Kerb has been around for years and it is a very good herbicide," said Fennimore. More than half the lettuce acreage in the state is protected against weeds with the compound.

"If we were to lose Kerb, it would be a serious disruption to lettuce production," he added.


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