Potato and Potato Blight (Phytophthora infestans)

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Potato and Potato Blight (Phytophthora infestans)

The potato (Solanum tuberosum) originated in the South American Andes and from there it was brought to Europe by Spanish traders about the year 1570. Sir Walter Raleigh has been credited with introducing the potato to Ireland, but it appears more likely that it was imported from Spain sometime between 1586 and 1600. The potato proved highly adaptable to the Irish soil and Ireland's cool, damp climate. In its first hundred years or so of cultivation, until about 1700, the potato was used as a supplementary food and as a bulwark against famine during years of poor corn yields. During the next fifty years, it became the staple food of the poorer classes during the winter months from October to March. The years between 1750 and 1810 saw dramatic growth in potato tillage and consumption, as the potato supported a rapidly growing population that increasingly depended on its sustenance for the greater part of the year. By 1845 some three million people had come to rely primarily on the potato as their staple food.

From about 1810 to 1845 a growing gap between food supply and demand led to increasing distress among the poorer classes, with ever more marginal land being pressed into service, little or no use of manures, and the increasing cultivation of the bulky but inferior quality "lumper" potato variety. The "lumper" had become the dominant variety in much of the country by 1845, and it was to prove highly susceptible to potato blight.

Potato blight is caused by the fungus phytophthora infestans, which attacks and rots the leaves and tubers of affected plants. Mild, humid, and wet weather conditions, common in Ireland, are particularly favorable to the spread of the disease. The blight that was to devastate Ireland was first seen in the United States in 1843 and in Belgium in June 1845. From there it spread rapidly across northwestern Europe, appearing in Ireland in August 1845. Its late arrival in Ireland reduced the impact on the 1845 harvest, but the yield was still about one-third below that required to feed the population. The following two years produced only about one-tenth of the prefamine harvest. With the ending of the blight after 1849 the potato supply slowly recovered, but it never again achieved its prefamine dominance in the Irish diet.

The decimation of the staple food source of at least three million people had inevitable and appalling consequences. About one million people died in the Great Famine;two million more left the country forever in the years between 1845 and 1855, many emigrating to the United States, Canada, and Australia, and others to Britain.