Researchers from the US and Norway have finally found the origin of Ireland’s Great Potato Famine, and shown that it actually originated in South America.
Scientists have long known that the fungus-like pathogen, Phytophthora infestans, was behind the tragic event, but up until now no one was sure where it came from, or how it made its way to Ireland.
After tracing the pathogen's evolutionary roots, the team found that P. infestans likely first originated in South America, travelled to the US, and eventually made its way to Europe where it caused potato and tomato crops to die off at unforeseen rates, leading to the Irish famine that claimed the lives of around 1 million people.
In case you have forgotten, the Great Irish Potato Famine was an event that took place in the 1840s, when Ireland's potato crops were infected with a type of blight, greatly reducing their yield. Seeing as so much of the population was dependent on the cheap root vegetable, this had disastrous effects.
It is estimated that roughly 1 million people died from starvation during the famine itself, and it triggered upwards of 1 million immigrants to flee from the nation to North America, causing Ireland’s total population to drop somewhere between 20 and 25 percent.
Despite the cause of the famine, P. infestans, being well known, researchers have debated where it came from and how it actually made its way to Ireland in the first place.
According to Stephanie Pappas from Live Science, scientists have previously hypothesised that the pathogen originated in multiple places, such as the Andes or Mexico, though there wasn't enough evidence to back up either claim.
Now, the mystery might have finally been solved thanks to researchers from North Carolina State University and the Norwegian University of Science and Technology Museum in Norway who have analysed the genomes of 183 samples of P. infestans from around the world to see how it evolved and moved before hitting the crops of Irish farmers.
To do that, the team analysed 12 key genome regions in the samples, creating a roadmap that they could track to see where certain strains arose.
Out of these samples, the team says that the lineage known as FAM-1 caused the blight in Europe and was also responsible for a late blight in the US in 1843. They also found that FAM-1 was first present in Colombia, leading them to hypothesise South America as its origin.
To analyse these results further, the team created a computer model to see how the patterns of mutations might spread throughout the world, finding that the most analytically sound scenario is that the pathogen popped up in South America, moved to North America, and then travelled across the Atlantic to Ireland and Europe, likely through trade.
"FAM-1 was widespread and dominant in the United States in the mid-to-late 19th century and the early 20th century," said corresponding author Jean Ristaino, from North Carolina State University.
"It also was found in Costa Rica and Columbia in the early 20th century."
Ristaino continues by saying that FAM-1 likely survived in the US for up to 100 years before getting displaced by a different strain called US-1, which they believe is sister lineage and not a descendant of FAM-1.
During those 100 years, though, FAM-1 made its way to Europe either by Europeans directly trading with South America, or infected US potatoes ending up there.
Either way, the strain spread to Europe where it devastated crops and triggered the devastating famine in Ireland.
Understanding how these pathogens work and spread might better protect us in the future, especially since modern technology has made it increasingly easier to trade with countries around the world.
It will take more research to completely figure out how the pathogen evolved in South America in the first place, but tracing its roots to Colombia might have finally solved a decades’ long mystery surrounding the deadly event in Ireland.
The team’s work was published in PLOS One.