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United States Department of Agriculture

Agricultural Research Service

Forensic Sleuths Use Biotechnology to Study Irish Potato Blight / March 17, 2000 / News from the USDA Agricultural Research Service

Potato infected with late blight

Read about research in Idaho (1998) and Maryland (1997) to develop potatoes with resistance to newer, more virulent strains of the blight fungus.

Read about related fungi that cause problems for U.S soybean growers. (1997)

Visit the U.S. National Fungus Collections on the World Wide Web.

Forensic Sleuths Use Biotechnology to Study Irish Potato Blight

By Hank Becker
March 17, 2000

Forensic plant pathologists investigating the fungus that caused the Irish potato blight are using tools of biotechnology as an aid in their sleuthing.

In 1845, a fungus—Phytophthora infestans—devastated Ireland’s potato crop. The blight caused the population of Ireland to drop from 8,200,000 to 4,400,000 from disease, starvation and emigration. Hundreds of thousands of Irish people emigrated to the United States.

Now, Agricultural Research Service scientist Carol L. Groves at the New England Plant, Soil and Water Laboratory, Orono, Me., and Jean B. Ristaino at North Carolina State University–Raleigh are examining the past to find clues to the future of this fungus.

They have studied genetic material, called DNA, from more than 66 herbarium samples of potato and tomato lesions to find clues about the source of fungal inoculum for past late blight epidemics. The researchers have examined samples from Europe and North America, including samples from the USDA-ARS National Fungus Collections, Beltsville, Md.

Looking for the fungus’ fingerprints, the scientists developed primers using polymerase chain reaction (PCR) technology to specifically amplify P. infestans DNA from the samples. PCR is capable of reproducing millions of copies of the unique segments of fungal DNA that occur in a plant tissue sample.

With this amplified DNA, the researchers can quickly distinguish the pathogens according to the specificity of the PCR amplification. By using PCR, scientists don’t have to isolate fungi from diseased roots or leaves and spend days culturing them for identification.

Rapid DNA identification of offending microbes would tip growers off to the need for control measures before fungal diseases seriously curtailed yields.

So far, the scientists have found 20 specimens that tested positive for the fungus, including one from Ireland collected in 1846, and others from Britain collected in 1845, 1846 and 1847.

Molecular studies of herbarium specimens of the past could open a new window to understanding and preventing future epidemics. ARS is the principal research agency the U.S. Department of Agriculture.

Scientific contact: Carol L. Groves, ARS New England Plant, Soil and Water Laboratory, Orono, Me., phone (207) 581-3267, fax (207) 866-0464,

Last Modified: 12/5/2006
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