The Irish Potato Famine was a food shortage in Ireland that killed 1 million people from 1845 to 1852. Prior to the potato famine, the working class in Ireland were highly dependent on a specific variety of potato for their diets: the Irish Lumper. Thus when potato blight struck the country the lack of genetic variability among plants caused the majority of the potato crops to turn to rotten mush.
It is estimated that 20% to 25% of the population of Ireland died from disease and starvation during the potato famine. Thousands of others fled the country. Today, the population of Ireland is 4.5 million – still less than its population before the potato famine.
In May 2013, the efforts of an international research team were published, announcing the discovery of a unique strain of potato blight called HERB-1, believed to be the cause of the Irish Potato Famine. Previously it was believed that the US-1 strain of phytopthora infestans was responsible for the Irish potato famine. HERB-1 was discovered by deciphering the entire genomes of eleven museum samples of potato blight in dried plants collected from 1845 to 1896, including some stored at the Royal Gardens at Kew in London. This is the first time that scientists have decoded the genome of a plant disease from dried samples. During their investigations, a mitochondrial genome that does not exist in present-day potato pathogens was found in the historical samples, leading them to conclude that an entirely new strain – HERB-1 – was the actual cause of the Irish Potato Famine.
Specimens of phytopthora infestans resemble fungi, but they are actually an oomycetes, a class of parasitic, algae-like organisms that feed on decaying matter.
The development of strains of phytopthora infestans correlates to the increase of global trade. For example, first contact between Europeans and Americans in sixteenth century Mexico is noted to have drastically increased the genetic diversity of potato blight. HERB-1 likely emerged during the early 1800’s through American potato shipments. As the new, HERB-1 resistant potato varieties were developed by crossing domestic potatoes with the wild potato solanum demissum, HERB-1 was supplanted by US-1, another strain of phytopthora infestans, to the extent that HERB-1 no longer exists in modern potato crops. US-1 in turn dominated the 20th century before being replaced by other strains.
Today, potatoes are the third most important food crop globally.
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