The Pathogen Behind the Irish Potato Famine: New Origins Revealed
A groundbreaking genetic study has unveiled new insights into the origins of Phytophthora infestans, the pathogen responsible for the Irish Potato Famine of the 1840s. Researchers have traced the devastating organism’s roots to South America, where it evolved before spreading to North America and ultimately Europe. This discovery provides a clearer understanding of the historical spread of the pathogen, which led to one of the most significant agricultural crises in history.
By comparing the genomes of P. infestans with those of its close relatives, including Phytophthora andina and Phytophthora betacei, researchers pinpointed the Andean region of South America as a hotspot for speciation—the evolutionary process where one species diverges into two or more. This genetic evidence refutes earlier theories suggesting a Mexican origin and highlights the critical role of global trade in the 19th century in the pathogen’s rapid spread.
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Professor Jean Ristaino from North Carolina State University, lead author of the study, explained,
“The Andean region is a hotspot for evolutionary divergence. By sequencing these genomes and studying migration patterns, we’ve gained critical insights into how this devastating pathogen emerged and spread globally.”
The potato blight caused by P. infestans destroyed crops across Ireland, leaving millions of people starving or displaced and causing profound societal and economic upheaval. Researchers believe that the pathogen’s arrival in Europe coincided with an increase in global trade, which facilitated its journey from South America.
Migration Patterns and Modern Implications
The study revealed significant historical migrations of P. infestans into and out of South America, with smaller exchanges between South America and Mexico. While earlier samples of P. infestans collected during the mid-19th century share ancestry with modern South American populations, the study emphasises that historical global trade was pivotal in shaping the pathogen’s genetic diversity.
Lead researcher Allison Coomber noted, “The data shows that in historic times, the Andean region was the primary source of P. infestans. Modern trade practices, however, have introduced more complex mixing of populations in South America, Europe, and Mexico.”
The findings also stress the importance of preserving genetic resources in the Andes, where wild potato species have co-evolved with the pathogen for thousands of years. This evolutionary relationship could hold the key to developing disease-resistant crops, a pressing need as climate change threatens traditional agriculture.
Professor Ristaino added, “Climate change is bringing drought and other challenges to higher Andean elevations, which puts these valuable wild potato species at risk. Preserving and studying these species is critical to combating late blight in the future.”
This article is based on findings from a study by North Carolina State University, titled “Study points to South America — not Mexico — as birthplace of Irish potato famine pathogen,” published on ScienceDaily on 24 January 2025. For more details, visit ScienceDaily
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[Feature Image Credit: An Irish family at the ruins of their house In Killarney. | Heritage Images/GettyImages]
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