Irish or white potato (Solanum tuberosum)

SOLANACEAE, Nightshade Family

The white or Irish potato (Solanum tuberosum), also called the "earth apple" (Fr. pomme de terre), needs no lengthy introduction. The tubers of this and other species were an important source of food to early South Americans, especially the Incas and their ancestors in the Andean highlands. In regions where climate is too cold for maize, natives have been able to grow potatoes; the archeological record of potato use dates back at least 13,000 years in Chile and 9000 years in Peru and Bolivia. In Peru the tuber is freeze-dried in the night air and then trampled (chuño) to make a starch staple, and this is added to stews with other tubers (oca, Oxalis tuberosa; melloco, Ullucus tuberosus). Potato is also used to make an alcoholic beverage called chicha.

White potato became an essential staple in the diets of common people throughout Europe. In Ireland, where the crop did extremely well, potato was the only staple food; e.g., male farm workers consumed 12-14 pounds of potatoes daily. In 1845, after three weeks of wet weather, the Irish potato crop began to die. The leaves and, subsequently, the tubers were infected with a fungus known as the late blight of potato, Phytophthora infestans, but only one person, Reverend M.J. Berkeley, knew and believed this. Tubers rotted, and from 1846 to 1851 nearly 1.5 million Irish (original population 8 million) died of starvation and other health complications. At the same time, over a million Irish people emigrated to the large eastern cities of the United States.

Solanum tuberosum is the fourth largest yielding crop plant in the world, behind wheat, rice, and maize, but compared with these three cereals, its production (nearly 225-285 million metric tons) occurs on 10% of the area. Potato trivia includes that this species is cultivated in 126 countries (1980 data), although Europe and the former Soviet Union contained 70% of the global potato area. One area in Switzerland produces 42 tons per acre, and other high yields come from the Netherlands and Israel. Five billion pounds of potatoes are made into fries every year!

Best potato production occurs where days are bright and sunny and nights are cool (50-57 degrees F). Highest tuber production is related to very high leaf area. Tubers form on stolons when the plant flowers, and they are no longer initiated after flowering. When the foliage dies with a frost, the tubers are harvested. About 7% of the crop is saved as "seed." A potato is cut into segments, which include at least one eye (a bud or node), from which emerge future shoots. (The starving Irish had to eat their seed potatoes during the famine, which left them with little for the next planting.) Potatoes to be eaten are stored at low temperatures (6 to 15 degrees C) to prevent buds from growing and to keep starch levels constant. Keeping them at higher storage temperatures is why they sprout in our pantries at home.

The potato is nutritionally very good, high in starch (8-28%) but with 1-4% protein in the inner layers of the skin (periderm, i.e., cork cells). This species also has some vitamin C. In addition to the usual eating of the tuber, white potato is used in the fermentation of vodka and for adhesives and sizing in paper and textiles. You should never eat a green potato--THEY ARE DEADLY POISONOUS if much is consumed. The poisonous substance is the alkaloid solanine, which is made in all green tissues of the plant.

As for late blight of potato--the disease is still around and causes problems wherever Irish potatoes are grown. The disease can be controlled by the application of Bordeaux mixture, a substance that was only tried on potatoes in 1892. Potatoes are subject to attack by as many as 250 pests, and researchers at the International Potato Center in Lima, Peru are attempting to use the gene pool of eight cultivated species, 3000 varieties, and from the 160 tuber-producing species of Solanum to yield new cultivars for feeding the people living in the Andes.

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