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Mystery solved: Strain of blight was responsible for the Irish Potato Famine

By Catholic Online (NEWS CONSORTIUM)
May 26th, 2013
Catholic Online (www.catholic.org)

A recently identified strain of potato blight, called "HERB-1," was responsible for mass starvation during the Irish potato famine in the 19th Century. At least a million people died of starvation at that time.

LOS ANGELES, CA (Catholic Online) - The precise strain of the pathogen that caused the devastating outbreak, which lasted from 1845 to 1852, had been unknown - until now.

"We have finally discovered the identity of the exact strain that caused all this havoc," study co-author Hernán Burbano, a researcher at the Max Planck Institute for Developmental Biology in Germany said.

Molecular biologists from across the world studied the historical spread of Phytophthora infestans, a fungus-like organism that devastated potato crops and led to the famine.

A Phytophthora strain called US-1 was at first thought to have triggered the famine. However, sequencing the genomes of preserved samples of the plant pathogen, the researchers discovered that a new, different strain the real culprit.

"Both strains seem to have separated from each other only years before the first major outbreak in Europe," Burbano said.

Studying 11 historic samples from potato collected about 150 years ago in Ireland, the United Kingdom, Europe and North America. Preserved at the Botanical State Collection Munich and the Kew Gardens in London, the leaves still had intact pieces of DNA. Some samples were so good, researchers were able to sequence the entire genome of Phytophthora infestans and its host, the potato, within a few short few weeks.

"The degree of DNA preservation in the herbarium samples really surprised us," study co-author Johannes Krause, a professor of paleogenetics at the University of Tübingen in Germany said.

Compared with modern Phytophthora strains from Europe, Africa and the Americas, the results enabled the researchers to trace the evolution of the pathogen, including where and when the HERB-1 and US-1 strains likely diverged.

The origins of the famine seems to have sprouted from sunny Mexico, as Phytophthora infestans first originated in Mexico's Toluca Valley. When Europeans and Americans first came to Mexico in the 16th century, the pathogen experienced increased genetic diversity, and in the early 1800s, the HERB-1 Phytophthora strain emerged and was brought out of Mexico.

By the summer of 1845, the HERB-1 strain had arrived at European ports, and the potato disease spread throughout Ireland and the United Kingdom, beginning the famine.

As new varieties of potatoes were introduced in the 20th century, the HERB-1 strain was eventually replaced by the US-1 Phytophthora strain, the researchers said.

This evolutionary change may have been spurred by the introduction of new crop breeding methods, which suggests that breeding techniques may affect the genetic makeup of plant pathogens.

"Perhaps this strain became extinct when the first resistant potato varieties were bred at the beginning of the 20th century," lead author Kentaro Yoshida, a researcher at The Sainsbury Laboratory in the United Kingdom said. "What is for certain is that these findings will greatly help us to understand the dynamics of emerging pathogens."

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