A genetic investigation has finally tracked down the source of the pathogen that caused the Irish potato famine, closing a case that has been up in the air for years. Researchers nailed down the Andes Mountains in South America as the birthplace of Phytophthora infestans, otherwise known as potato blight or late blight.
The pathogen, taking the form of a fungus-like microorganism (oomycete/water mold), has devastated potato and tomato plants throughout history. A new study published in the journal PLOS One settled the debate on the spread of P. infestans, delivering insight on its progression throughout the centuries.
Conflicting Pathogen Hypotheses
Previously, the debate on the origins of P. infestans was solidly split into two camps; many scientists believed the pathogen first cropped up in central Mexico, a widely accepted view. Others, however, maintained that it instead arose farther down in South America. The new study lends strong support to the South American hypothesis due to genetic likeness among P. infestans and certain related pathogens.
Researchers compared whole genomes of P. infestans with Phytophthora andina and Phytophthora betacei, close relative pathogens that are only found in South America. The results indicated that these three species were very similar.
“It's one of the largest whole-genome studies of not only P. infestans, but also the sister lineages,” said Jean Ristaino, a professor of plant pathology at North Carolina State University and corresponding author of the study, in a press release. “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.”
Conversely, the study found that P. infestans showed distinct differences from two Mexican pathogen species, P. mirabilis and P. ipomoea.
Read More: The Domino Effects of a Global Food Shortage
How Did the Pathogen Cause Famine?
The study seemingly confirmed that P. infestans moved from South America to North America. In 1843, reports of the disease in the United States were first recorded around the ports of Philadelphia and New York. Soon after, it was transported to Europe on a cargo of potatoes, and by 1845, it ruined potato crops across Belgium, the Netherlands, and southern England.
P. infestans made its way to Ireland, which heavily depended on potatoes — they were a staple food for at least two-thirds of the population, including many agricultural laborers. The pathogen struck a major blow to the nation's potato crop, leaving widespread poverty and disease in its wake. The Great Famine that ensued, lasting from 1845 to 1852, marked a major crisis in Irish history that depleted the population due to death and emigration; around one million people died during this period, and closer to two million left the country.
Potato blight continues to threaten potatoes and tomatoes globally, as it causes an estimated annual loss of $6.7 billion worldwide.
Throughout the years, researchers have looked to potato species that offer some level of resistance against P. infestans. The primary focus in the past has been on Solanum demissum, a wild potato species native to Mexico and Guatemala containing alleles that provide pathogen resistance. However, a pressing concern is the ability for the pathogen to mutate into variants that can breach the defenses of a potato that was previously resistant. As a result, the need to find new sources of resistance is key.
Resistance in the Andes
The realization that the pathogen first came out of the Andes Mountains has brought attention to the possibility of pathogen resistance existing in the region.
“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 said in the release.
Understanding the evolution of P. infestans up until this point may now help researchers discern where they'll need to look next to potentially find new sources of resistance.
“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 in the release. “Modern global trade appears to contribute to mixing together the pathogen populations in South America and Mexico.”
Article Sources
Our writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article:
Scientific Reports. Reconstructing historic and modern potato late blight outbreaks using text analytics
Ireland's Great Hunger Museum. Learn About the Great Hunger
RHS. Potato blight
U.S. Department of Agriculture. Wild Potatoes Tapped for Late Blight Guard Duty
Jack Knudson is an assistant editor at Discover with a strong interest in environmental science and history. Before joining Discover in 2023, he studied journalism at the Scripps College of Communication at Ohio University and previously interned at Recycling Today magazine.
