The potato was important because the Irish population grew from 3.5 to 8 million between 1700 and 1840.  Economic relationships between Ireland and England were factors in the impending disaster such as increasing population, exploitation by land owners, enforced exports of food crops to England, poor housing conditions and low standard of living, dependence on potato for food.  High field crop producing a very healthy food with little labor investment.  Irish were potato people and were remarkable healthy with potatoes as appetizer, dinner and dessert. Many Irish survived on milk and potatoes alone and the two together provide all essential nutrients while others subsided on potatoes and water, or a little cabbage and salt.  By the early 1840s, almost one-half of the Irish population had become entirely dependent upon the potato, specifically on just one or two high-yielding varieties.  From 1845 to 1852, the Irish potato production was ravaged by blight.  Blight accounted for crop loss of anywhere from one third to one half of all acreages planted in 1845.  Three quarters of the crop was lost 1846.  Seed potatoes were scarce for many years following these two devastating years, limiting recovery.  The result of the potato blight was mass starvation, disease, and emigration in Ireland between 1845 and 1852.  It was also called Irish Potato Famine since 2/5 of population was solely reliant on the cheap potato crop.  1 million or more died and emigrated from Ireland between 1846 and 1851, mainly to North America.

Phytophthora infestans was the pathogen responsible for the Irish Potato Famine.  The disease led to widespread famine, and nearly all of the few potatoes available were eaten, causing shortages of seed potatoes that ensured starvation would continue for nearly a decade,  Ultimately, over one million people died, and another million emigrated to escape the disaster, causing Ireland’s population to fall by roughly 25 percent.  The island has still not reached its pre-famine population levels today.  Currently, P. infestans is distributed worldwide, with the vast majority comprised of the destructive strain US-1.  Most of the other strains of P. infestans occur only in Mexico’s Toluca Valley, where wild potato varieties are indigenous, so scientists long believed that US-1 had been responsible for the 1840s famine.