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Farmer's foe. Verticillium causes wilt and death of potato leaves.

Alfalfa Gene Beats Potato Scourge

By plucking a gene from alfalfa and plunking it into potatoes, scientists have created potato plants that resist a pervasive fungal disease. The accomplishment, reported in the December issue of Nature Biotechnology, marks the first time that effective resistance to any fungus has been obtained through the transfer of a gene between plant species.

Farmers and gardeners alike fear Verticillium dahliae, a persistent soil-borne fungus that is widespread throughout the world's temperate regions. The pathogen attacks dozens of crops, from tomato plants to pistachio trees, causing devastating losses. The first line of defense against the fungus is to breed resistant varieties of plants, but traditional methods require many years and massive field trials.

A group of researchers at Monsanto Co. in St. Louis tried genetic engineering instead, and they began by searching for genes that confer resistance to Verticillium. By screening compounds from plants immune to the disease, the researchers found a protein in alfalfa that could slow or even halt growth of Verticillium and certain other fungi. When amino acid analysis revealed that the protein was a defensin--a diverse group of small proteins with antimicrobial activity--the team named it alfalfa antifungal peptide, or alfAFP.

The researchers used a bacterial vector to transfer the alfAFP gene into plant cells of America's favorite baked and french-fried potato, the Russet Burbank, a variety with no resistance to Verticillium. They then selected the most resistant plants from among their transgenic creations and compared them in small greenhouse and field trials to Russet Burbank and another variety bred to resist Verticillium, called Russet Ranger. The incidence of disease in the best transgenic line was about three to five times less than in Burbanks and about equivalent to that in Rangers.

Plant disease experts are greeting the announcement with guarded optimism, stressing that data on yields, toxicity, and other agronomic factors are not yet available. "Yields are often reduced when genes are introduced," cautions Jim Davis, retired potato disease specialist from the University of Idaho, Aberdeen. Yet, if the gene proves effective in potatoes, Davis says, it would provide breeders with a potent tool that may work in other crops, as well.

To complicate matters, the discovery comes at a time when bioengineered crops face an unclear future. Resistance to transgenic foods is strong in many countries, and exports of U.S. corn have plummeted since September, when traces of a transgenic variety not yet approved for human consumption were found in taco shells. "This is rapidly shifting terrain," says agricultural economist Desmond Jolly from the University of California, Davis. Before embracing new transgenic crops, "more and more farmers will be hedging their bets," Jolly says, "waiting to see how consumer demand and perhaps regulatory responses evolve in the future."

Related sites
More on Verticillium dahliae
Biotechnology in vegetable production, from the University of California
Monsanto
Union of Concerned Scientists biotechnology Web site
Agricultural biotechnology information, sponsored by the biotech industry