The potato famine in Ireland killed a million people and led to mass emigration. The potatoes were destroyed by late blight, caused by the water mold Phytophthora infestans. And we now know exactly which strain of the water mold did the dirty work.
Researchers analyzed dried potato leaves, well over a century old, from Ireland, as well as Europe and North America. They were able to sequence the genomes of 11 different strains of blight, and then to compare these older specimens to 15 modern ones.
Their conclusion: a strain called HERB-1 was responsible for the Irish Great Famine. The work is in the journal eLife. [Kentaro Yoshida et al., The rise and fall of the Phytophthora infestans lineage that triggered the Irish potato famine]
A strain called US-1 had previously been thought to be the culprit. And the two strains are closely related. HERB-1 held sway during the 19th century, but with the introduction of new kinds of potatoes in the 20th century, US-1 began to dominate.
Similar work with other preserved plant specimens could help trace the evolutionary history of other pathogens. And assist the ongoing effort to keep our staple crops disease-free.
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