St. Louis Post Dispatch

Monsanto Genetically Engineers Potato That Resists Common Fungus

Scientists at Monsanto Co. have genetically engineered a potato to resist a common fungal disease.

The feat marks the first time researchers have been able to make fungus-defying potatoes by inserting a single gene. Other attempts produced potatoes that withstood fungal diseases in the laboratory, but not in the field.

"Fungal diseases in general have been one of the tougher challenges for biotechnology," said Monsanto's David M. Stark, who heads the company's potato business.

In the December issue of Nature Biotechnology, the Monsanto researchers report that potatoes engineered with a protein from alfalfa can ward off a common fungus.

The fungus - Verticillium dahliae - lurks in the soil and kills young plants, robbing farmers of yield, Stark said. Potato growers lose between $70 million and $140 million in profits to the fungus every year.

The fungus is usually kept in check by fumigation of the soil, Stark said. Fumigation kills both the fungus and some harmful nematodes, but is not a particularly attractive option for most growers because of the cost and health hazards from the chemicals.

"Soil fumigants are not the most worker-friendly chemistry," Stark said. Potato farmers spend about $75 million to control the fungus each year.

The scientists isolated a protein from alfalfa that makes the plant naturally resistant to Verticillium. When they tested the protein - called alfAFP, for alfalfa anti-fungal protein - in the lab, it stopped the fungus from growing. The protein also halted the growth of two other plant fungi that cause early blight in potatoes and head scab, a wheat disease.

The protein was not effective against Phytophthora infestans, the potato late blight fungus that caused the Irish potato famine of 1845-1851.

Although the scientists aren't sure how the protein stops fungi from growing, evidence suggests that the alfalfa protein latches on to a molecule called chitin and stops the fungus from making cell walls, Stark said.

Chitin is the sugary chemical that makes up the hard outer covering of insects and the shells of lobsters and crabs. The famine blight is from a different family of fungi, which do not have chitin in their cell walls, so the alfalfa protein has nothing to grab on to.

The Monsanto researchers inserted the gene for the fungus-fighting protein into susceptible Russet Burbank potatoes, the most commonly used potato variety in the United States.

In laboratory trials and field tests in Illinois, Wisconsin and Oregon, the newly-engineered potato resisted the fungus as well as Russet Ranger potatoes, a naturally fungus-resistant potato.

And potatoes containing the alfalfa gene resisted the fungus just as well as fumigated spuds, the researchers said.

If the engineered potato passes further tests, it could be a significant advance in fighting fungal infections, said William E. Fry, a plant pathologist at Cornell University in Ithaca, N.Y.

"If the initial results are consistent and carry through, this is going to be a nice contribution," he said.

The scientists still have to demonstrate that their fungus-fighting spud is otherwise identical to the Russet Burbank potato and that it is safe for human consumption and the environment, Fry said.

The fungus-resistant potatoes won't make an appearance on the dinner table anytime soon. Stark estimates that it will take another eight to 10 years to bring the spud to market.

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