A Famine, Revisited
We’ve been blaming the Irish potato famine on the wrong culprit.

By John Farrell, Institute for Education & Research, Beth Israel Deaconess Medical Center, Boston.
June 18, 2001 9:00 a.m.

t's no secret that Phytophthora infestans has long been a term of unremitting dread to the Irish and their descendants since the days of the Great Famine.

Phytophthora what...?

Okay, the potato blight. The disease that wiped out the potato crops that caused the Great Famine, which killed over a million Irish peasants and drove another million plus into exile. Phytophthora infestans has long been considered the culprit, because until now genetic testing relied on DNA from modern-day late-blight outbreaks, and scientists assumed it was the same. Russia is suffering the worst attack, although smaller blights continue to ravage Ireland, Mexico, Ecuador, and the United States.

But according to new DNA evidence published in last week's issue of Nature — Phytophthora infestans wasn't the culprit in Ireland after all. North Carolina State University plant pathologist Dr. Jean Beagle Ristaino and her team analyzed the DNA of 150-year old Irish potato leaves kept from the famine preserved in the British Royal Botanic Gardens in Kew, England. "Our data emphasize the importance of using actual historical specimens,". she said. Her study is the first ever to isolate and analyze mitochondrial DNA from historic specimens.

Ristaino expected to find traces of the 1b haplotype, or strain, of late-blight Phytophthora infestans. Instead, she found one of three other late-blight candidates. No traces of Phytophthora infestans.

Why is this important? After all, it's not like this is really going to change the history books or make the Irish feel any better. (On the other hand — some of the Irish Famine memorials built around the world may need some touching up.)

Ristaino said, "Identifying the geographic center of origin for late blight is important, because that's where you're most likely to find host resistance — potato plants that have developed natural resistance to the pathogen — that can be used to breed new, more resistant potato varieties for widespread use."

According to her team's paper, the pathogen may have originated in South America rather than Mexico where it was believed to originate. But Ristaino concedes that much more research is needed before scientists can be certain "...because the South American collections are not as complete or well-studied as they should be."

Knowing how the pathogen has spread, and how it has mutated or evolved over the years, would be helpful, according to Ristaino, because it could aid scientists in developing better control measures to prevent future epidemics.

Doesn't it figure? Not being able to stop the Famine from killing so many peasants, some enterprising English scientists figured, "What the hell, we may as well collect some of the deadly leaves for posterity." And only now they turn out to be truly helpful!

That's the luck of the Irish for you.