Nearly two centuries later, researchers believe they have identified the pathogen that led to Ireland's deadly potato famine. To make their discovery, British, German, and American scientists sequenced DNA from samples of dried potato leaves collected between 120 and 170 years ago, reports PhysOrg. They identified the particular strain of Phytophthora infestans in samples dating to 1845, the year the pathogen arrived in Ireland, then compared the genetic information to that of today's plants, the BBC reports.
As PhysOrg explains, researchers had previously believed US-1, today's major pathogen, was the culprit. Instead, they found that a new strain, dubbed HERB-1, triggered the outbreak. Scientists believe HERB-1 appeared at the beginning of the 19th century and wasn't replaced by US-1 until the 20th century, when new potato varieties were planted. ("We can't be sure but most likely [HERB-1 has] gone extinct," says one scientist.) Besides solving a 168-year-old mystery, the find has big implications: It marks the first time the genome of a plant pathogen has been decoded using dried, preserved plant specimens, and paves the way for similar research in the future.