Armed with a new gene, spuds fend off blight. (Stout Potatoes).

It has been more than 150 years since the Irish potato famine, when the funguslike disease called blight annihilated the staple food for millions of people. But blight is still the most serious potato disease in Europe, the United States, and the rest of the world. Farmers spend billions of dollars annually on fungicides to keep blight at bay.

Now, genetic engineering may give potato crops built-in resistance to the pathogen. By placing a gene from a naturally blight-resistant wild potato into a farmed variety, researchers from the University of Wisconsin-Madison and the University of California, Davis have made plants that are invulnerable to a range of blight strains.

The scientists suspected that a four-gene cluster in the wild potato species Solanum bulbocastanum was responsible for its resistance to blight. They cloned the genes and spliced one gene into each of four batches of potato plants. When they exposed these new cultivars to blight, one group stayed healthy, suggesting that the gene it received was conferring resistance. The scientists named the gene RB, for resistance from bulbocastanum.

Lead researcher John Helgeson of Wisconsin says that S. bulbocastanum probably developed resistance to blight because it coevolved with the pathogen in Mexico, where blight is widely believed to have originated. Helgeson and his colleagues publish their findings in the July 22 Proceedings of the National Academy of Sciences.

"If what they have shown in the greenhouse really happens in the field, this has major promise for creating resistance to blight," comments Autar Mattoo of the U.S. Department of Agriculture's vegetable laboratory in Beltsville, Md.

Blight is caused by various strains of the funguslike organism Phytophthora infestans, which thrive under warm, moist conditions. All strains infect the potato plant's foliage, scarring it with lesions and blocking photosynthesis.

Scientists have known about S. bulbocastanum's resistance to blight since the 1950s. But of the scores of potato varieties bred around the world for frying, baking, boiling, and chipping, none has been successfully crossed with S. bulbocastanum. Some of those varieties won't interbreed with their wild cousin, while others lose their best culinary traits when crossed with wild potato plants. Helgeson and his team decided to bypass these difficulties using genetic engineering.

He says that the blight-resistant plant his group created could be ready for field-testing within about a year.

As a genetically modified food, however, the ultimate acceptance of the potatoes by the world community remains a big unknown. "That's not a scientific question," Helgeson notes.

The environmental benefits of the modified plant are compelling, he adds: "By transferring this gene from one potato to another, we can greatly reduce the reliance on pesticides."

Helgeson and his colleagues now aim to unravel how the RB gene enables potatoes to stand up to blight. If the researchers succeed, they might even open a way to circumvent the row over genetically modified foods. It might be possible, Helgeson says, to design a new antiblight pesticide based on S. bulbocastanum's natural defenses.