Irish Potato Famine Pathogen Identified (revised)

Although it came too late to help the Irish of the 19th century, British scientists have sequenced DNA from potato leaves in museums to identify the pathogen that caused the blight that became the Irish Potato Famine. It's name? Phytophthora infestans-HERB 1. According to the report in the BBCNews, the researchers think that this strain has probably disappeared as a result of potato breeding. However, that doesn't mean that potatoes are home free.

The researchers believe the strain - HERB-1 - emerged in the early 1800s and continued to spread globally throughout the 19th Century.

Only in the 20th Century, after new potato varieties were introduced, was it replaced by another Phytophthora infestans strain, US-1, which is now dominant around the world.

Although the story for a long time was that the blight originated in the US and crossed the Atlantic on a trading ship, NBCNews reports that these researchers believe the DNA traces the blight to Mexico:

By mapping the genetic differences between the 19th-century samples and 15 modern-day strains of blight, the scientists could reconstruct the pathogen's evolution over the centuries. They determined that the blight originated in Mexico's Toluca Valley. The species' genetic diversity increased markedly in the 16th century, around the time that Spanish explorers settled the New World. That era marked the wider spread of potato varieties, and probably hastened the evolution of Phytophthora infestans as well.