The pathogen responsible for the Great Irish Potato Famine that killed thousands in Ireland and led to the Irish emigrating across the globe, evolved thousands of miles away from the Emerald Isle, in the Andes mountain range of South America, a new study has found.
Researchers from North Carolina State University in the United States conducted a wide-ranging study of the genetic material found in Phytophthora infestans, the pathogen responsible for the famine, along with other members of the Phytophthora species.
They found that P infestans spread from South America to North America before wreaking havoc in Ireland in the 1840s. It is still responsible for late blight in tomato and potato plants worldwide.
The researchers compared whole genomes of P infestans with those of close relative pathogens — Phytophthora andina and Phytophthora betacei — which are only found in South America.
“It is one of the largest whole-genome studies of not only P. infestans, but also the sister lineages,” said Jean Ristaino, William Neal Reynolds Distinguished Professor of Plant Pathology at North Carolina State University and corresponding author of the study.
“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,” Ristaino added in a statement by the university.
In July last year, Down To Earth had reported how a study by researchers from the Boyce Thompson Institute, also in the US, had shown Peru rather than Mexico to be the place of origin of P. infestans.
The experts from North Carolina State University reached a similar conclusion.
Allison Coomber, a former NC State graduate student researcher and lead author of the paper, noted that the researchers’ data showed 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 also in reverse, because there’s a big Mexican potato breeding program and potatoes have gone into the Andean region in more recent times. But in historic times it was the other way around.”
“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. “Modern global trade appears to contribute to mixing together the pathogen populations in South America and Mexico.”
The paper, titled A pangenome analysis reveals the center of origin and evolutionary history of Phytophthora infestans and 1c clade species, has been published in PLOS One.
Its authors are Allison L. Coomber, Amanda C. Saville, Ignazio Carbone, Michael Martin, Vanessa C. Bieker and Jean Beagle Ristaino.