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In the mid‑19th century, Ireland endured the Great Famine, a catastrophe that claimed roughly 1 million lives and forced a further 2 million to emigrate. The disaster was triggered by the collapse of the potato crop, which constituted the main diet for about half of the population.
The culprit was Phytophthora infestans, a pathogen that causes late blight, rapidly killing potato tissue. For years, scientists debated whether the pathogen originated in Mexico or elsewhere in South America before spreading northward and eventually reaching Europe. A comprehensive genomic study by researchers at North Carolina State University has now clarified its origins.
Published in PLOS One, the study shows that P. infestans can be convincingly traced to the Andes Mountains. This aligns with historical accounts that Andean farmers were aware of the disease long before it spread to the rest of the world. The finding reshapes our understanding of the pathogen’s history and has significant implications for managing future epidemics worldwide.
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By sequencing whole genomes of P. infestans and its close relatives—Phytophthora andina and Phytophthora betacei, which are endemic to South America—NC State scientists identified striking genetic similarities that pinpoint the Andes as a hotspot for speciation.
“By analyzing these genomes alongside evolutionary relationships and migration patterns, we demonstrate that the Andean region is a crucible for speciation,” explained Jean Ristaino, one of the paper’s authors. “This is one of the largest whole‑genome studies of P. infestans and its sister lineages.”
Earlier hypotheses favored central Mexico as the origin, but the new data reveal limited migration out of Mexico compared to the robust gene flow from South America. While some recent movement from Mexico into the Andes is evident, the historical pattern shows the pathogen moving northward from its South American cradle.
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The discovery forces a reassessment of historical spread models and highlights the need to focus breeding efforts on Andean germplasm to develop durable resistance. With climate change intensifying droughts in the Andes, the very genetic diversity that may hold the key to resistance could vanish before it is fully characterized.
“Ultimately, managing blight hinges on host resistance,” said co‑author Jean Ristaino to The Guardian. “Our work underscores the necessity of prioritizing Andean breeding programs.”
Future research must identify a sexually reproducing P. infestans population in South America, as current Andean strains reproduce asexually, accumulating unhelpful mutations. Until such a population is found, the definitive origin remains an active scientific debate. For more on cross‑border species movements, explore the invasive species affecting Indiana.
