Imma Perfetto
Cosmos science journalist
Scientists might have been looking in the wrong place to find the original source of potato blight, which could prevent discovery of ways to avoid the problem.
Late blight of potato and tomato, was the cause of the Great Hunger, the Irish potato famine, but it remains a problem around the world. Determining where the pathogen that causes it came from originally could help discover ways that native potato plants resist the disease.
A new study suggests that the microorganism, Phtytophthora infestans, originated from the South American Andes Mountains, before spreading to North America and Europe.
P. infestans is a type of single-celled eukaryote known as an oomycete, or water mould, which destroys the leaves and edible parts of potatoes, tomatoes, and some other nightshades. Potato blight which destroyed crops, and lack of a welfare safety, led to the starvation and death of more than one million people during the Irish great famine in the 1840s.
In recent decades, the question of whether P. infestans originated from Mexico or South America has divided scientists. In a new PLOS ONE study, researchers analysed the whole genome sequences of P. infestans and related species to determine the answer.
“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 2 or more distinct species,” says Jean Ristaino, professor of plant pathology at North Carolina State University in the US and corresponding author of the paper.
Lead author Allison Coomber, a former NC State graduate student researcher and current bioinformatics scientist at Monoceros Biosystems, adds: “Our data shows 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.
“We did find there was gene flow from the Andes to Mexico, and in reverse, because there’s a big Mexican potato breeding program and potatoes have gone into the Andean region in more recent times,” she says.
“But in historic times it was the other way around.”
The findings add support to a South American origin of the pathogen and suggest that examining wild Andean potato species could help researchers learn more about resistance to late blight.
“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 says.
“It points out the importance of looking at the centre of origin where a host and pathogen have evolved together over thousands of years.
“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.”
