Potato ranks as one of the world’s most important, popular, and widely grown vegetables. A highly nutritious food, the potato forms a basic part of human diets in many countries.
People eat potatoes fresh or in processed forms. Popular ways of preparing fresh potatoes include baking, boiling, French-frying, or mashing. Processed potatoes commonly appear as potato chips, frozen French fries, and instant mashed-potato powder or flakes. Other processed foods use potatoes as a key ingredient. They include canned hash, stews, and soups. Manufacturers also use potatoes in flour, vodka, industrial starch, and a kind of alcohol called ethanol.
A potato consists of about 80 percent water and 20 percent dry material, which is mostly starch. These percentages vary depending on the potato cultivar (variety) and on the conditions in which the cultivar is grown. In general, potatoes with a higher proportion of starch make better baked potatoes, potato chips, and French fries. Potatoes with a lower proportion of starch make better boiled potatoes and better ingredients in canned potato products.
The dry material in potatoes contains many substances called nutrients necessary to promote human growth and health. They include proteins, vitamins, minerals, and fibers. Potatoes provide an especially rich source of potassium and vitamin C. A raw potato that weighs about 6 ounces (170 grams) contains around 130 calories.
The world’s potato growers produce about 400 million tons (360 million metric tons) of potatoes annually. China grows the most potatoes of any country. Other leading potato-growing nations include India, Russia, Ukraine, and the United States.
People grow hundreds of potato cultivars worldwide, and breeders produce new ones each year. Cultivars may differ in size, shape, color, texture, or taste. One of the leading types, the Russet Burbank, has long proved popular as a fresh potato and as a potato for processing. Manufacturers widely use the Atlantic variety to make potato chips. Other cultivars include the Austrian crescent, Kufri Jyoti, Mira, Nevsky, Red Norland, and Yukon gold.
The potato plant
The edible parts of a potato plant are thick, underground stems called tubers. They grow at the ends of longer underground stems called rhizomes or stolons. Most potato plants develop from 3 to 20 tubers, depending on the variety and the growing conditions. Tubers generally have a round or oval shape, but some varieties take a long fingerlike form. They range in size from less than 1 inch (2.5 centimeters) to more than 10 inches (25 centimeters) long. The largest potatoes, often used to make French fries, can weigh 1 pound (0.45 kilogram) or more. A potato’s relatively thin skin may have yellow, brown, white, pink, red, or blue coloring. Most tubers have white flesh inside, though some cultivars possess yellow, pink, or blue flesh.
Tubers consist of several layers of material. The outer skin is called the periderm. The next layer, the cortex, serves as a storage area for protein and some starch. The third layer, known as the vascular ring, receives carbohydrates from the plant’s leaves and stem, as well as water and nutrients from the roots. The carbohydrates turn into starch and accumulate in parenchyma cells, the tissue that surrounds the vascular ring. Parenchyma cells provide the tuber’s main storage areas for starch. The center of the tuber, called the pith, consists mostly of water.
The part of the potato plant that grows above ground typically has spreading stems and coarse green leaves. It grows from 2 to 5 feet (60 to 150 centimeters) tall. Depending on the variety, white or purplish flowers appear from 4 to more than 10 weeks after the plant starts to sprout. In some cultivars, the flowers develop seedballs that resemble small green tomatoes. Each seedball contains several hundred seeds. Scientists use these seeds when developing new cultivars.
Growing potatoes
Planting and cultivating.
Potatoes grow best in warm areas with day temperatures of about 75 °F (24 °C) and night temperatures of about 55 °F (13 °C). Growers must replant potatoes annually because the plants die after the tubers mature. In warmer regions, farmers often plant potatoes in the fall and winter. Growers from colder regions plant in spring and early summer. Harvesting takes place from 70 to 180 days after planting.
Growers cultivate potato plants from seed potatoes, using either whole potatoes called seed tubers or cut pieces of potatoes called seed pieces. The best seed tubers or seed pieces weigh about 2 ounces (60 grams). Each has at least one eye (bud), from which a sprout can grow. Breeders carefully develop seed potatoes to reduce the possibility of disease.
Commercial farms use machines that plant up to six rows of seed potatoes at a time. Tubers grow relatively close to the soil surface, so farmers plant the seeds only 2 to 4 inches (5 to 10 centimeters) deep. They then add more soil to form hills 2 to 6 inches (5 to 15 centimeters) high. Such hills ensure that the soil temperature remains warm enough for the tubers to grow well. The hills also prevent tubers from exposure to sunlight. Exposure can cause greening and other damage to the growing potatoes. Planters space the seed potatoes 10 to 18 inches (25 to 46 centimeters) apart in rows 30 to 36 inches (76 to 91 centimeters) apart. Furrows (narrow grooves) form between the seed hills.
Potato crops in drier locations need irrigation. Growers also must add such nutrients as nitrogen, potassium, and phosphorus to the soil before or during planting. In some areas, farmers should continue to add nitrogen while the plants are growing.
A potato plant’s foliage will begin to die off when the plant matures. To make harvesting easier, farmers must completely kill the vines. They can do so by removing the foliage mechanically or by drying up the vines with chemicals called desiccants.
Potato pests.
Fungi, bacteria, and viruses cause diseases that may attack potatoes. Fungal potato diseases include early blight, late blight, and rhizoctonia. Bacterial diseases include blackleg, ring rot, and common scab. Viral diseases include potato leafroll and mosaic.
Planting healthy seed potatoes will considerably reduce the chances of disease infecting a potato crop. Farmers should purchase seed that has been certified as healthy. To further combat fungal diseases, including early and late blight, growers may spray their plants with chemicals called fungicides.
Insects attack all parts of a potato plant. Stems and leaves can fall victim to aphids, leafhoppers, potato beetles, and potato psyllids. Flea beetles, potato tubeworms, and wireworms attack the tubers themselves. Aphids, leafhoppers, and potato psyllids can also transmit harmful viruses to potato crops.
Chemicals called insecticides can help control insect pests. Before or during planting, farmers may spray insecticides into the furrows between the seed hills. The potato plant’s roots absorb these chemicals and eventually spread them to the stems and leaves. Growers also may spray insecticides on the leaves after they sprout.
Many weeds infest potato crops as well. Such weeds include Canada thistle, field bindweed, lamb’s-quarters, and various nightshades and pigweeds. Gardeners control weeds by hoeing or pulling them by hand. Commercial growers often control them by applying chemicals called herbicides before or after the weeds emerge.
Harvesting.
Most commercial potato growers use potato combines to harvest their crops. These machines dig the plants out of the ground, separate the tubers from the soil, and load the potatoes onto trucks.
Some growers send the potatoes directly to the processing plant or the packing shed. There, workers grade and size the tubers and remove unappealing ones. Most growers, however, must store their harvested potatoes for a time. Potato storage places should provide a dark, humid environment with adequate air. Depending on what the potatoes will be used for, storage temperatures will vary. Seed potatoes require the lowest storage temperature, about 38 °F (3.3 °C). Potatoes used for processing need the highest temperatures, from 45 to 50 °F (7.2 to 10 °C). Warmer storage temperatures ensure that the starch in processing potatoes will not convert to sugar. Higher sugar levels make these potatoes turn darker when cooked, resulting in less desirable potato products.
Potatoes will start to sprout in storage after several months. To prevent sprouting, growers may apply chemicals called sprout inhibitors on all varieties except seed potatoes. Proper storage techniques enable people to sell and consume potatoes the year around.
History
The potato originated in the Andes Mountains of South America. Scientists believe cultivated potatoes came from a species that first grew around Lake Titicaca, in what are now Bolivia and Peru. Before European explorers arrived in those regions during the early 1500’s, people living in the valleys of the Andes Mountains grew potatoes. They preserved their potatoes by freeze-drying them into a crusty substance called chuno, which they could keep indefinitely.
Spanish explorers in South America first brought potatoes back to Europe around 1570. Once introduced in Europe, potatoes soon spread to other parts of the world. They became a vital food source in many regions, especially Ireland.
Potatoes probably first arrived in North America in the early 1600’s. But they did not become a major food crop until after Irish immigrants brought the plants with them when they settled in Londonderry, New Hampshire, in 1719.
From 1845 to 1847, Ireland’s potato crop failed because of late blight. Due to this and other factors, about 1 million Irish people died of disease or starvation. About 11/4 million others left Ireland and settled in other countries, chiefly the United States. In the late 1990’s, a new strain of late blight reduced potato harvests throughout the world.
During the 1900’s, advances in food processing techniques greatly increased the production of such potato products as French fries and potato chips. Today, processing plants use most of the potatoes grown worldwide.
