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Wednesday, 6 June, 2001, 18:02 GMT 19:02 UK
Wrong culprit blamed for potato famine
Potato harvesting
Potato blight is still a problem in many parts of the world
DNA analysis of ancient potato leaves has forced scientists to re-think their theories about the origin of the Irish potato famine.

More than one million people starved and another two million emigrated to America when Ireland's potato crop was devastated in the 184Os.


Historic collections can be valuable to epidemiologists and population geneticists who study plant diseases

US research team
Until now, scientists believed the crop failure was caused by a particular strain of fungus, originating in Mexico.

But molecular detective work carried out on historic samples preserved at London's Kew Gardens pinpoints one of three other strains, probably from South America.

"Herbarium collections have not been used previously to understand epidemics of the past and track pathogen migrations," says the US team behind the discovery, in the scientific journal Nature.

"Our work indicates that these historic collections can be valuable to epidemiologists and population geneticists who study plant diseases."

Wrong culprit

Potato blight is still a major problem in many countries - affecting crops in Russia, Mexico, Ireland, Ecuador and the US.

Experts now know that a fungus causes the disease. When plants become infected, lesions appear on their leaves and stems. Eventually the potatoes rot and become inedible.

Until now, scientists had always believed that a common strain of the fungus that arose in Mexico caused the Irish potato famine.

But DNA analysis shows that this is not the case. Researchers at North Carolina State University, Raleigh, say that identifying the real culprit - one of three strains - could have important implications for reducing the risk to crops.

By finding where the disease arose, it might be possible to find plants that are naturally resistant to the disease and use them to breed more resistant varieties of potato.

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