Irish Potato Famine: Devastating Pathogen Originated In South America

Researchers may have finally tracked down the origin of Phytophthora infestans, which is the pathogen responsible for the 19th century Irish potato famine. After some careful ancient DNA detective work, scientists from the University of California (UC) Berkeley and the University of Copenhagen believe the fungus-like organism originated in South America.

The catastrophic Irish potato famine began in 1845 and lasted for six long years, during which time millions of people died. Potatoes are not native to Ireland, but they likely originated in South America and quickly became an Irish staple because they were rich in protein, carbohydrates, minerals and vitamins -- and easy to grow in the country's cool moist soil.

In the recent study, researchers analyzed genome sequences of 71 modern and historical samples of the microbial pathogen to get a better sense of how it evolved and made the historical transatlantic leap that destroyed potato crops, according to a news release. After constructing the pathogens' ancestral trees, they discovered the origin of the species dates back to 1558 AD, which is when the first Europeans explored South America.

"We think early European activities in the New World led to the origin of this devastating pathogen. Countless improbable events led to the introduction of this species to Europe in 1845, but our work narrows down the evolutionary possibilities to exactly two," Mike D. Martin, study leader and a  postdoctoral researcher at UC Berkeley, explained in the release.

After the pathogen evolved and diversified it found its way into Europe during the 19th century. The ancient P. infestans represents the strand linked to the catastrophic 1845 outbreak. However, researchers also found a close connection between a present-day sister species known as P. andina, which can only be found in the highlands of Ecuador and Peru.

Therefore, the pathogen's evolutionary history suggests it either spread directly into the U.S. after being found in South America, or appeared in South America and the U.S. simultaneously after traveling from Mexico, prior to spreading throughout Europe. However, further study is required to trace its exact route into Europe.

"Ultimately finding the precise location where this species evolved could lead potato breeders to discover new genetic tools for improving resistance against potato blight disease," Martin added in the release.

Their study was recently published in the journal Molecular Biology and Evolution.

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