More than one million people died in the Irish Potato Famine of the mid-19th century, with another million migrating to America and elsewhere, making 40 percent of Irish-born people part of the diaspora by 1914.

For decades leading up to the "Great Hunger," inept aristocrats and an absent Church within the UK failed to diversify the food sources, and by the time famine struck, one-third of Irish people subsisted primarily on the potato crop.

Now, new research from an international team of scientists sheds light on the pathogenic cause of the potato blight that wiped out the isle's staple food, from a specimen collected in 1847 during the height of the famine. For the first time, scientists have used dried samples to decode the genome of a plant and associated pathogen, exploring the evolution of such diseases within the plant kingdom as well as our influence on their lives.

"We have finally discovered the identity of the exact strain that caused all this havoc", Hernán Burbano, from the Max Planck Institute for Developmental Biology in Germany, told media.

Phytophthora infestans, a eukaryotic microorganism, changed the course of human history, as even today the population of Ireland has yet to fully recover and more than 36 million people worldwide claim Irish as their primary ethnic heritage. To be published in the online journal eLife, the research analyzed the spread of the potato pathogen, which devastated the crop across Europe during those years. In contrast to previous research, investigators found a new strain of the pathogen that separated from the only a few short years before the first major outbreak, Burbano said.

Kentaro Yoshida from The Sainsbury Laboratory in Norwich, UK, also described the research. "Herbaria represent a rich and untapped source from which we can learn a tremendous amount about the historical distribution of plants and their pests — and also about the history of the people who grew these plants," he said.

The historic samples, dried and saved for posterity, were compared to modern strains of the pathogen from Europe, Africa, and the Americas, as well as to two related species. The investigators estimated that the various strains diverged from each other after a progenitor emerged in the early 1800s, sweeping the globe during that century. Only later, however, was the pathogen replaced by a new strain.

Interestingly, the scientists were able to connect events in human history with the genetic record of the plant pathogen, with a "remarkable increase in the genetic diversity of phytopthora" observed upon first contact between Europeans and Native Americans in Mexico in the 16th century. The clash of civilizations may have led to a spread of the pathogen from its birthplace in Toluca Valley, Mexico, which in turn sped its evolution.

The team correlated the pathogen's genetic record with human historical events after decoding the genome of 11 historical samples of the organism from potato leaves collected over a half century from Ireland, the UK, Europe, and North America, preserved in the Botanical State Collection Munich and Kew Gardens in London.

Yoshida said the findings would greatly help researchers understand the dynamics of emerging pathogens, with implications for the world's future food supply.