The Source Of The Deadly Irish Potato Famine Has Ties To The Andes Mountains

The source of the pathogen that caused the Irish potato famine has finally been identified. Researchers from North Carolina State University have pinpointed the Andes Mountains in South America as the pathogen’s place of origin.
The pathogen, Phytophthora infestans, also known as potato blight, is a fungus-like microorganism that has wreaked havoc on potato and tomato plants around the world for centuries. It still affects crops today, causing an estimated annual loss of $6.7 billion globally.
A new genetic study provides evidence that P. infestans spread from South America to North America before devastating Ireland in the 1840s.
In the study, whole genomes of P. infestans were compared to closely related pathogens, Phytophthora andina and Phytophthora betacei.
“It’s one of the largest whole-genome studies of not only P. infestans, but also the sister lineages,” said Jean Ristaino, a co-author of the study and a professor of plant pathology at North Carolina State University.
“By sequencing these genomes and accounting for evolutionary relationships and migration patterns, we show that the whole Andean region is a hot spot for speciation, or where a species splits into two or more distinct species.”
In recent decades, the debate on the origins of P. infestans was split between two different theories. Some scientists believed the pathogen first emerged in Mexico. However, others thought it arose in South America.
The new study shows distinct differences between P. infestans and two Mexican pathogens, confirming that P. infestans originated in South America and moved to North America.
Reports of the disease in the United States were first recorded in 1843 around the ports of New York and Philadelphia.

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Soon after, it was transported to Europe via a cargo of potatoes. By 1845, it ruined potato crops across the Netherlands, Belgium, and southern England.
Eventually, P. infestans made its way to Ireland, which depended on potatoes. They were a staple for the majority of the population, including agricultural workers.
The pathogen destroyed the nation’s potato crop, causing The Great Famine, a time of widespread poverty and disease that lasted from 1845 to 1852.
Around one million people died during this period, and almost two million left the country. Throughout the years, researchers have looked for potato species that are more resistant to P. infestans.
“A lot of the search for resistance to this disease has focused on a wild potato species in Mexico—Solanum demissum—which was used to breed resistant potato lines that were used for the past 100 years,” said Ristaino.
“It points out the importance of looking at the center of origin where a host and pathogen have evolved together over thousands of years.”
But the concern is that the previously resistant pathogen will mutate into variants that can bypass the defenses of a potato. As a result, it is necessary to find new sources of resistance.
The revelation that P. infestans came from the Andes Mountains has called attention to the possibility of existing resistant potato species in the region.
According to Ristaino, climate change is bringing more drought to higher elevations in the Andes, so these potatoes may become lost before researchers can figure out if they can provide resistance to P. infestans. Understanding the evolution of P. infestans can help them find new sources of resistance.
The study was published in the journal PLOS One.
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