Irish Potato Famine Pathogen Origins Tracked to South America with Ancient DNA

New ancient DNA detective work may have revealed the origins of the Irish potato famine pathogen. Researchers have discovered that the fungus-like organism originated in South America.

The pathogen itself is called Phytophthora infestans, and researchers have long wondered how it was introduced to Europe. In order to find out, the scientists used genome sequences from 71 modern and historical samples of the microbial pathogen, a unique collection culled from private archives worldwide. This allowed the scientists to reconstruct the ancestral tree of this pathogen.

So what did they find? The origin of the species dates back to 1558 AD, which is when Europeans explored South America. The species was first introduced to 19^th-century Europe shortly after it evolved and diversified. There was an especially close connection between present-day sister species, P. andina, and the ancient P. infestans that triggered the catastrophic Irish potato famine.

It's likely that after being found in South America, the pathogen either spread from South America to the U.S., or was simultaneously introduced from Mexico into South America and the U.S. prior to its infestation of Europe.

"We think early European activities in the New World led to the origin of this devastating pathogen," said Mike Martin, one of the researchers, in a news release. "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. 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."

The findings are published in the journal Molecular Biology and Evolution.

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