Researchers at North Carolina State University have pinpointed the Andes Mountains as the birthplace of the infamous Irish potato famine pathogen, Phtytophthora infestans.
This pathogen, responsible for devastating potato and tomato crops globally, originated in South America and spread across continents in the mid-19th century.
Origins of the Irish Potato Famine Pathogen
Call it a mystery solved.
Researchers from North Carolina State University have traced the origins of the Irish potato famine pathogen, Phytophthora infestans, to the Andes Mountains in South America.
Through an extensive genetic analysis of P. infestans and its close relatives, the researchers provide strong evidence that the pathogen originated in South America before spreading to North America and eventually reaching Ireland in the 1840s. Even today, P. infestans continues to cause late-blight disease, a devastating threat to potato and tomato crops worldwide.
Genomic Evidence Links Pathogens to the Andes
The study compared the complete genomes of P. infestans with two closely related species — Phytophthora andina and Phytophthora betacei — both of which are native to South America. The findings reveal striking genetic similarities among these species, reinforcing the theory of the pathogen’s South American origin.
“It’s one of the largest whole-genome studies of not only P. infestans, but also the sister lineages,” said Jean Ristaino, William Neal Reynolds Distinguished Professor of Plant Pathology at North Carolina State University and corresponding author of a paper in PLOS One that describes the study. “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.”
Controversy and Clues in Pathogen Origin
In recent decades, scientists have been split in their theories about the point of origin for P. infestans, with some hypothesizing a Mexico origin rather than a South American origin. Yet, the paper shows distinct differences between P. infestans and the two Mexican pathogen species, P. mirabilis and P. ipomoea.
“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,” Ristaino said.
Climate Change and Wild Potato Species
“It points out the importance of looking at the center of origin where a host and pathogen have evolved together over thousands of years,” she said. “Climate change is bringing more drought to higher Andean elevations, so we could be losing some of these potatoes before we learn if they could provide resistance to late-blight disease.” Ristaino added that more research is needed to examine wild potato species from the Andes to learn more about host resistance to P. infestans.
“Our data show that there have been more migrations of the pathogen into and out of South America, and the migrations into and out of Mexico are small in comparison,” said Allison Coomber, a former NC State graduate student researcher and lead author of the paper. “We did find there was gene flow from the Andes to Mexico, and also in reverse, because there’s a big Mexican potato breeding program and potatoes have gone into the Andean region in more recent times. But in historic times it was the other way around.”
Historical Divergence and Modern Trade
“Historic P. infestans – the samples collected from 1845-1889 – were the first to diverge from all other P. infestans populations, with modern South American and Mexican populations both showing shared ancestry derived from historic P. infestans,” Ristaino said. “Modern global trade appears to contribute to mixing together the pathogen populations in South America and Mexico.”
“A pangenome analysis reveals the center of origin and evolutionary history of Phytophthora infestans and 1c clade species”
Reference: “A pangenome analysis reveals the center of origin and evolutionary history of Phytophthora infestans and 1c clade species” by Allison L. Coomber, Amanda C. Saville, Ignazio Carbone, Michael Martin, Vanessa C. Bieker and Jean Beagle Ristaino, 24 January 2025, PLOS ONE.
DOI: 10.1371/journal.pone.0314509
Authors: Allison Coomber, Amanda Saville, Ignazio Carbone and Jean B Ristaino, NC State University; Michael Martin and Vanessa C. Bieker, Norwegian University of Science and Technology
Amanda C. Saville, a research and laboratory specialist in Ristaino’s lab, and Ignazio Carbone, a professor of plant pathology at NC State, also co-authored the paper, along with Michael Martin and Vanessa Bieker from the Norwegian University of Science and Technology. Funding was provided by a National Science Foundation National Research Training Grant (award number 1828820), and by two USDA APHIS Plant Protection Act 7721 grants: AP21PPQ&ST000020 and AP21PPQ&ST000062.
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