Potato Famine Mystery Solved

From History in the Headlines:

Scientists have long known that it was a strain of Phytophthora infestans (or P. infestans) that caused the widespread devastation of potato crops in Ireland and northern Europe beginning in 1845. P. infestans infects the plant through its leaves, leaving behind shriveled, inedible tubers. The most likely culprit, they believed, was a strain known as US-1, which even today is responsible for billions of dollars of crop damage each year. To solve the mystery, molecular biologists from the United Kingdom, Germany and the United States examined DNA extracted from nearly a dozen botanical specimens dating back as far as 1845 and held in museum collections in the UK and Germany, which were then sent to the Sainsbury Laboratory in Norwich, England. After sequencing the genome of the 19th century samples and comparing them with modern blights, including US-1, they were able to trace the genetic evolution of P. infestans around the world and across centuries.

The researchers concluded that it wasn’t in fact US-1 that caused the blight, but a previously unknown strain, HERB-1, which had originated in the Americas (most likely in Mexico’s Toluca Valley) sometime in the early 19th century before spreading to Europe in the 1840s. HERB-1, they believe, was responsible for the Great Famine and hundreds of other potato crop failures around the world. It wasn’t until the early 20th century that improvements in crop breeding yielded potato varieties that proved resistant to HERB-1 that the deadly infection was stopped in its tracks. Scientists believe that the HERB-1 strain is now extinct.

First domesticated in southern Peru and Bolivia more than 7,000 years ago, the potato began its long trek out of South America in the late 16th century following the Spanish conquest of the Inca. Though some Europeans were skeptical of the newly arrived tuber, they were quickly won over by the plant’s benefits. Potatoes were slow to spoil, had three times the caloric value of grain and were cheap and easy to grow on both large farms and small, backyard lots. When a series of non-potato crop failures struck northern Europe in the late 18th century, millions of farmers switched to the more durable spud as their staple crop. (Read entire article.)

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