Irish Potato Famine: How Did Scientists Discover Its Cause 170 Years Later?

By iScienceTimes Staff on May 22, 2013 2:05 PM EDT

Potato blight
Scientists have discovered the exact strain of pathogen responsible for the Irish Potato Famine, 170 years after it began. Around one million lives were lost due to the potato blight. (Photo: Creative Commons)

Scientists have finally discovered the blight that caused the Irish Potato Famine.

While scientists have long known that the pathogen Phytophthora infestans caused the mid-19th century famine, only now have they identified the exact strain that led to the roughly one million famine deaths.

The long-held assumption in the scientific community was that a strain of Phytophthora infestans called US-1 was behind the potato famine. To verify that assumption, a team of researchers from the U.K., Germany and the U.S. used dried plants from botanical gardens and museums, and looked at the pathogens which felled them. They compared the pathogens of 11 dried potato samples, which were over 100 years old, and compared them to 15 modern pathogen strains. They found that the pathogen responsible was a unique strain which they've dubbed HERB-1.

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"This strain was different from all the modern strains that we analyzed-most likely it is new to science," said Sophien Kamoun, a co-author of the study. He added that US-1 and HERB-1 are closely related.

According to the study, which is to be published in eLIFE, HERB-1 originated in Mexico's Toluca Valley before spreading far and wide.

"The Spanish introduced Europeans to the South American staple crop potato shortly after their conquest of the New World," the authors write, "but for three centuries Europe stayed free of P. infestans."

The authors believe that a strain of the pathogen left Mexico at the turn of the 19th century, separating into HERB-1 and US-1. Seed potatoes with the pathogen crossed the Atlantic from the U.S. to Belgium, according to the New York Times, at which point spores of the pathogens spread far and wide in the wind.

This is the first time the scientists have used dried herbarium samples to crack a plant pathogen's genome.

"The degree of DNA preservation in the herbarium samples really surprised us," said Johannes Krause from the University of Tübingen, one of the study's co-authors.

The study's lead researcher, Kentaro Yoshida, was similarly enthusiastic about the effectiveness of studying century-old plants.

"Herbaria represent a rich and untapped source from which we can learn a tremendous amount about the historical distribution of plants and their pests--and also about the history of the people who grew these plants," he said. "This type of work paves the way for the discovery of many more treasures of knowledge hidden in herbaria."

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