The Potato Plant
The Family: Solanaceae
The potato (Solanum tuberosum) is a tuberous-rooted tropical and subtropical plant grown in temperate countries as an annual. It is mostly used as a vegetable, a source of starch, and for other commercial purpose. Though not widely grown in home gardens, it can be a most satisfying producer. Two pounds of certified seed potatoes can give you fifty pounds of potatoes for eating.
The potato is the staple food crop for many people around the world, people whose ancestors had subsisted upon grain crops for several thousand years prior. The reason for this change is that the potato is the best all-around source of nutrition known to mankind. The writer and commentator, John Read, made the following observations on the well-known radio program Man on Earth in 1988:
"The biological value of potato protein (an index of the nitrogen absorbed from a food and retained by the body for growth and maintenance) is 73, second only to eggs at 96; just ahead of soybeans at 72, and far superior to maize at 54, and wheat at 53. Potatoes also contain significant amounts of essential vitamins (the British, in fact, derive 30 percent of their vitamin C intake from potatoes). Exceptional productivity is another virtue of the potato. A field of potatoes produces more energy per acre per day than a field of any other crop. It grows from sea level to 14,000 feet on a wider variety of soils, under a wider range of climatic conditions, than any other staple food. The potato matures faster than any other staple, in 90 to 120 days, and will provide small but edible tubers in just 60 days. All in all, the potato is just about the world's most efficient means of converting plant, land, water and labor into a palatable and nutritious food."
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The plant is bushy, sprawling and dark green with compound leaves that somewhat resemble those of its relative, the tomato. (Compound means consisting of a number of parts of leaflets, rather than a single flat leaf blade.) The potato leaf has one long leaflet in the center with two to four pairs of side leaflets, all part of the same leaf. The leaves are arranged in a spiral around the stem. Clustered, 1-inch wide, 5-petaled flowers range in color from white to pale-blue to purple. Marie Antoinette wore these flowers in her hair. The plant is completely poisonous except for the tubers. All plant members of the nightshade family, which includes potatoes, tomatoes and eggplants, contain the poisonous alkaloid called solanine. The fruits of both tomatoes and eggplants are their only edible parts. Though at one time used as a treatment for asthma, bronchitis and epilepsy, solanine can make people very sick. The potato plant uses solanine as a natural defense from its many predators.
(Plant picture from National Geographic, May 1982, Vol 161, No 5.)
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The life cycle of the potato plants we grow today is tuber to sprout to plant to tuber. But in the beginning was the seed. When a seed is planted, it sprouts, pushing a shoot upwards out of the soil and a root downwards into the soil. The seedling uses its energy to grow leaves to develop into a full-grown plant. When the rapid leaf growth slows down, the plant begins to form flowers, and belowground, special stems called stolons begin to branch out and swell at their tips. Because the leaves in the potato plant are producing more starch than they need, the extra is sent down through the plant to the stolons. The starch is deposited at the ends of the stolons forming tubers. The tubers will grow larger and larger as more and more starch is produced by the plant.
When the potato plant has set its fruit and formed its tubers, it dies. But the tubers are still a live plant, "breathing", using oxygen that passes through their pores and giving off carbon dioxide. Each tuber has several small indentations in it called "eyes" which are covered with tiny scales. Because the tubers are still alive, they will send up new stems called "sprouts" out of one or more of the eyes. Some will be fat and hairy; some will have clearly developed leaf buds. The starch in the potato will continue to support the growth of a new plant until it is all used up.
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The tuber can be planted. Growers use a "seed potato", a piece of a tuber with an eye. The seed potato is planted, using the starch within it to start growing a new plant. When the plant is large enough, it will start producing enough plant starch for its own growing needs. The cycle then completes itself for the grower; tuber to sprout to plant to tubers; tubers for both harvest and for planting the next growing season.
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The potato's yellow-green fruit is rarely seen. It looks somewhat like a cherry tomato with 100 to 300 seeds per fruit. Each seed is able to grow its own plant, which will either look like the parent plant that provided the pollen or the parent plant that provided the seeds. But it also may be that the flower was pollinated by pollen carried by wind or insect from another field. Because the grower can't be certain beforehand what his plants will be like if he plants seed, the grower will plant tubers instead.
Modern potato breeders need seed to develop new varieties of potatoes. But because seed balls are not used for planting, they are rarely seen on modern plants. In fact, some of today's potato plants do not produce any seeds at all. This is a problem for modern potato breeders but they get around it by planting a potato plant onto a tomato rootstock. The plant's energy does not go into growing tubers; instead the plant produces seedballs.
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There are a number of varieties of potatoes that are grown throughout the world. The ones below are grown and sold by Sunspiced, Inc.
R usset Norkotah
The Russet Norkotah was released in 1987 by North Dakota State University. It is early-maturing. Plants are small and bloom sparsely with white flowers. Tubers are oblong to long, medium to heavy russeted, and have medium dormancy. Eyes are numerous, medium deep and surrounded by non-russeted skin. Its flesh is white. Russet Norkotah yields are greater than the Russet Burbank. This variety can consistently produce 80 percent or more U.S. No. 1's with excellent uniformity of shape and appearance.
The Norkotah has low specific gravity typically in the range of 1.070 - 1.080. It is not suitable for processing into french fries; sugars accumulate rapidly if not stored properly. However, it is an excellent potato for dehydration or for tablestock. Vitamin C concentration in tubers is similar to the Russet Burbank.
The Norkotah is susceptible to several common potato diseases, but is resistant to blackspot and shatter bruise, common scab, leafroll net necrosis, early blight tuber lesions and growth cracks.
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The Russet Burbank was selected from the Burbank variety sometime before 1912. It is late-maturing. Plants are large and spreading and bloom sparsely with white blossoms. Tubers are long and cylindrical with russet skin. Eyes are shallow, numerous and well distributed. Its flesh is white. Yields range from 200-400 cwt/acre (hundred weight per acre) in eastern Idaho and up to 500 cwt/acre in western Idaho. Yields in eastern Washington can range from 500-600 cwt/acre. Russet Burbanks account for 85% of the Washington State potato crop. In all growing areas 40-80 percent of the crop are U.S. No. 1's. Its specific gravity ranges from 1.075 - 1.095.
The Russet Burbank is a multipurpose potato suitable for both fresh market and processing. It is excellent for baking and processing into frozen and dehydrated products. This variety has long dormancy and stores well at 45° F and higher without accumulating excess sugars. It can be stored at 45° F for 5 months without sprout inhibition or for 10-12 months with sprout inhibition.
Under adverse growing conditions, the Russet Burbank can develop external and internal defects such as secondary growth, sugar-end and hollow heart. The variety is very susceptible to leafroll net necrosis and verticillium wilt, and moderately susceptible to most other common potato diseases.
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The Russet Goldrush variety was released by the North Dakota Agricultural Experiment Station in 1992 and was selected from a cross of Lemhi and ND450-Russ. It is a medium-maturing, oblong variety with smooth, light brown russet skin. Its flesh is extremely white. The plants are quite large and virulent with sparse white blooms.
The Goldrush is a fairly high yielding plant which averages 350-400 cwt./acre. It produces 70-85% U.S. No.1s with a desirable blocky shape and higher percentages of baking size potatoes than many other varieties. The Goldrush has a specific gravity which ranges from 1.065 to 1.080. Although not suitable for french frying, this variety is a good choice for table stock because it bakes and boils well.
A drawback to the Goldrush variety is its short dormancy period in storage. If left untreated, it will sprout earlier than other Russet varieties. It has some resistance to verticillium wilt and blackspot bruising, excellent resistance to hollow heart and good scab resistance.
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The Red Norland variety was released from North Dakota State University in 1958. The Red is a very early-maturing, light red-skinned variety. Plants are medium in size and bloom moderately with dark red-purple blossoms; tubers are round to oblong and slightly flattened. The plants produce a high percentage of U.S. No. 1 tubers.
The Dark Red Norland was selected in 1989 from the Red Norland variety by researchers in the Red River Valley. It is an early-maturing variety with deep purple-red skin. The tuber color is enhanced when grown in heavier, darkier soils such as muck and loam. Plants are medium-sized with long broad leaves and pink flowers. Dark Red Norlands typically require longer periods after vine-kill and before harvest to achieve strong skin set than Red Norlands. Yields generally range from 250-350 cwt./acre.
Both Red and Dark Red Norlands have very low specific gravity ranges and are not suitable for dehydration. They are excellent for fresh frying and salads, boiling and mashing. The deep skin color of the Dark Red is especially appealing to consumers and chefs when prepared with the "jacket on". They are sold in multiple sizes of A's, B's and C's (largest to smallest). Since the late 1980s and early 1990s, the popularity of "baby reds" has soared and the B and C sizes command a premium price on the fresh market. Because they are not used for processing, low temperature storage (39°F) can be used for both Red and Dark Red Norlands.
Red Norlands are susceptible to early dying, viruses, foliar damage from early blight, and sensitive to metribuzin injury. But they are resistant to leafroll, net necrosis, growth cracks, hollow heart and tuber damage by early blight. Dark Red Norlands are particularly susceptible to water damage, greening and enlarged lenticel infections. The variety is scab resistant.
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This category contains almost any variety not fitting into the Round White, Russet, or Red categories. These specialty varieties are used exclusively for the fresh market. The Purple has deep purple skin and almost irridescent purple to blue flesh. Boiled or mashed, its flesh is striking. The Yukon Gold has yellow skin and warm yellow flesh. Both Yukon Gold and Purple varieties are excellent tablestock. Restaurants can use these potatoes to striking advantage.
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