Irish Potato Famine Pathogen Identified From Dried Museum Samples

A team of scientists has identified a unique strain of potato blight which they believe triggered the Irish potato famine in the 19th century.

Farmers lose crops to disease regularly, but sometimes the pathogens that infect plants are so powerful that blight occurs, leading to devastating losses. In the case of the Irish potato famine from 1845 to 1852, a million people died from starvation and another million left Ireland in search of food, causing the island's population to fall by as much as 25 percent.

Using DNA extracted from museum specimens, researchers determined that the strain of potato blight that caused the 1845 famine is different from modern day potato blights and is probably now extinct. The study was the first time scientists have decoded the genome of a plant pathogen and its plant host from dried samples.

Although the dried plant samples were as many as 170 years old, researchers were still able to extract many intact pieces of DNA.

"This strain was different from all the modern strains that we analyzed - most likely it is new to science," Sophien Kamoun of The Sainsbury Laboratory in Norwich told BBC News.

"We can't be sure but most likely it's gone extinct."

Kentaro Yoshida from The Sainsbury Laboratory said that dried plant samples in museums "represent a rich and untapped source from which we can learn a tremendous amount" about the historical distribution of plants and their pests.

The pathogen that caused the Irish potato famine is a fungus-like oomycete known as Phytophthora infestans. A strain of the pathogen known as US-1 was long thought to cause the great famine, but the current study concludes that a similar, but previously unknown, strain was responsible. Scientists have named the new strain HERB-1.  

"Both strains seem to have separated from each other only years before the first major outbreak in Europe," said Hernán Burbano from the Max Planck Institute for Developmental Biology.

Speaking with the BBC, Yoshida said the strain may have gone extinct when the first resistant potato varieties were bred at the beginning of the 20th century.

The research is published in the open-access journal eLife.