Irish potato famine pathogen came from US: study

The pathogen that caused the Irish potato famine in the 1840s - which left mass starvation, disease and migration in its wake - first set down roots in the US before attacking Europe, say scientists who mapped the evolution of the disease.
Researchers theorise that the pathogen arrived in Europe via infected potatoes on South American ships or directly from infected potatoes from the US.
They tracked the evolution Phytophthora infestans, the pathogen responsible for the Irish potato famine and a major cause of late-blight disease on potato and tomato plants around the world.
Researchers from the North Carolina State University in the US studied 12 key regions on the genomes of 183 pathogen samples - historic and modern - from across the globe.

The study shows that a lineage called FAM-1 caused outbreaks of potato late blight in the US in 1843 and then two years later in Great Britain and Ireland.
It was also found in historic samples from Colombia suggesting a South American origin.

FAM-1 caused massive and debilitating late-blight disease outbreaks in Europe, leaving starvation and migration in its wake.
However, FAM-1 was not just a one-hit wonder that made its mark and then quickly disappeared.
"FAM-1 was widespread and dominant in the US in the mid-to-late 19th century and the early 20th century," said Jean Ristaino, Professor at NC State.

"It also was found in Costa Rica and Columbia in the early 20th century," said Ristaino.
"FAM-1 survived for about 100 years in the US but was then displaced by a different strain of the pathogen called US-1. US-1 is not a direct descendant of FAM-1, but rather a sister lineage," she said.
US-1, in turn, has been elbowed out of its eponymous homeland by even more aggressive strains of the pathogen that have originated in Mexico. Our winter vegetable crops, grown there and imported into the US, harbor the pathogen, she said.
The pathogen's effects are not limited to the decimation of Ireland's potato crop 170 years ago.

Billions are spent worldwide each year in attempts to control the pathogen, Ristaino said. Potatoes in the developing world are particularly vulnerable as fungicides are less available and expensive.
The study was published in the journal PLOS ONE.