The DNA of a 150-year-old potato has forced scientists and historians to re-examine the commonly held theory about the origin of the infamous Irish potato famine.

During the 1840s, more than one million people starved and another two million emigrated to America when Ireland’s potato crop was devastated. Contemporary clerics blamed the disaster on the devil, but in 1846 a scientific theory expounded by the Reverend Miles Berkeley gradually became widely held as the predominant reason for the famine. Berkeley blamed a fungus for infecting the crop, making lesions appear on leaves and stems until the potatoes rot and become inedible.

Later, scientists would confirm that the strain that attacked Ireland, 1-b haplotype (or US-1), originated in Mexico.
Recent molecular detective work and DNA fingerprinting carried out on historic samples of Irish potatoes points to the existence of one of three other strains, however. Researchers at North Carolina State University believed that identifying the real fungus culprit behind the famine would help scientists to breed more resistant crops, as fungus is still a problem in many countries around the world, including the US and Russia.

Publishing the findings in today’s edition the scientific journal Nature, Prof Jean Ristaino, Gregory Parra and Dr Carol Groves reveal: “The old theory was that the 1-b haplotype was the ancestral strain, originating in Mexico. Our research refutes the first half of that theory, and calls into question the second half.”

Speaking to the Daily Telegraph newspaper, Ristaino added: “There is a good possibility that the pathogen evolved where the potato evolved, in South America. We are continuing our work with a more extensive collection of worldwide specimens from the 19th century to confirm or refute this hypothesis.”

Importantly, the researchers made their conclusions by looking at potato samples that had been preserved at London’s Kew Gardens. As the article comments: “Herbarium collections have not been used previously to understand epidemics of the past and track pathogen migrations […] our work indicates that these historic collections can be valuable to epidemiologists and population geneticists who study plant diseases.”