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Cut-open potato infected with blight: Link to photo information

Potato Late Blight May Be Arrested Earlier

By Doris Stanley and Linda Cooke
May 28, 1997

Growing potatoes without fungicides to control late blight may be only about 5 years away, because of research progress at finding potatoes with natural resistance.

Caused by the Phytophthora infestans fungus, late blight triggered the Great Irish Potato Famine of the 1840's. New, severe strains can destroy a crop within weeks. They’ve swept through the world in 6 years--and been found in Idaho, Washington, North Dakota, Colorado, Oregon, Minnesota, Michigan, Maine and Wisconsin. Some strains resist metalaxyl, the fungicide that controls the original type of late blight. U.S. losses are estimated at hundreds of millions of dollars over the past several years. Worldwide losses amount to $3 billion annually.

Scientists at the Agricultural Research Service and universities evaluated 17 potato clones reported having some natural resistance. Of the top four clones, three came from the ARS Vegetable Lab, Beltsville, Md., and one from the ARS potato breeding program at Aberdeen, Idaho. ARS has released two Beltsville clones to other breeders. These two selections resist the most virulent late-blight strains. Some less-resistant clones still would need less fungicide than commercial varieties.

Several years ago, ARS scientists in Madison, Wis., discovered natural resistance in a wild Mexican potato species. They combined its genes with those of commercial potatoes. The resulting breeding line, grown without fungicides, yielded 20 tons of spuds per acre in field tests last year. The scientists recently developed a gene probe from the wild species. It may let breeders determine if potato seedlings are resistant even before they’re planted. This would speed availability of resistant varieties for farmers.

A story about the research appears in the May issue of Agricultural Research, ARS’ monthly magazine. The story also is on the World Wide Web at:


Scientific contacts: Kenneth L. Deahl, ARS Vegetable Laboratory, Beltsville, Md., phone (301) 504- 7380, fax 504-5555,; and John P. Helgeson, ARS Plant Disease Resistant Research Unit, Madison, Wis., phone (608) 262-0649; fax 262-1541; e-mail