Commercial potato production is a complex and highly specialized commercial enterprise that demands a high degree of technical skill and practical experience on the part of the producer. With the trend toward increased processing use of potatoes since the middle of 1950's, it has become necessary for growers to orient their production practices to the type of market in which they expect to sell. Nonetheless, these newer processing operations which manufacture chips, frozen, and dehydrated products provide important, large outlets which have reversed the declining per capita consumption of potatoes in the United States.

The continued application of farming technology has resulted in markedly less acreage required to produce more food. In the 1930's, between three and three and one half million acres (1.2 and 1.4 million ha) of potatoes were harvested in the United States, but in the 1980's about 1.3 million acres (0.5 million ha) produced more than one and one-half times the tonnage grown in the 1930's (Table 1). Average yields of potatoes have increased steadily, and with further shifts westward to the high-yielding, irrigated fields of Washington and Oregon, the national average yield reached 290 cwt per acre (32.5 t/ha) in 1990. Increased yields have resulted from shifts in geographical areas of production, shifts to fewer but larger farms, marked changes in mechanization, and several improved cultural techniques.

Table 1. U.S. land area, yield and production of potatoes selected years 1930-1990

Source: Agricultural Statistics Board, NASS, USDA

In Canada, much the same trend exists with about one-half million acres (0.2 million ha) of potatoes being planted in the 1930's and only 300,000 acres (122,000 ha) in the late 1980's with about 50 percent more tonnage in the 1980's than in the 1930's (Table 2). Average yields have also increased in Canada by more than 2 times since the 1930's. Yield reported in Canada is substantially lower than the U.S. because Canada's major production is from non irrigated acres.

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Table 2. Canadian land area, yield and production of potatoes selectedyears 1925-1990

Source: Statistics Canada

History

Most botanists agree that the potato originated in the New World, though the exact locality of origin is uncertain. Historians record that the Spaniards found potatoes in Peru at the time of their conquest of the country beginning in 1524. The native home of the potato is often claimed to be in the Andes of Peru and Bolivia at altitudes of 4,000 to 6,000 feet (1220 to 1829m), where its very close botanical relatives flourish even today.

Historians disagree about the first introduction of the potato into Europe. There is good evidence, however, that the Spaniards introduced the potato from South America to Spain by 1580, or even as early as 1565. Hieronymous Cardan, a monk, is supposed to have been the first to introduce it from Peru to Spain. From Spain the plant was taken into Italy about 1585, into Belgium and Germany by 1587, into Austria by 1588, and into France soon after 1600. Philip de Sivry, Prefect of Mons, Belgium, sent two potato tubers to Carolus Clusius in Vienna, Austria, where they were received on January 26, 1588. Philip de Sivry had received a plant from an attache' of the Papal Legation; he, in turn, had obtained plants from Italy. De Sivry's colored drawing, now in the Plantin-Moretus Museum at Antwerp, Belgium, was probably named soon after 1588 and is considered by some writers to be the first European illustration made of the potato. However, the first published illustration and description was by Gerard, an English botanist. It appeared in 1597. Gerard, unfortunately, gave it the misleading name of Batata virginiana, and thereby created confusion as to the origin, history, and proper identification of the potato. The accepted botanical name Solanum tuberosum was first used in 1596 by the Swiss botanist, Kaspar Bauhin, and this was the name adopted in 1753 by Linnaeus in his Species Plantarum.

Introduction of the potato into England probably was independent of its spread in Europe. The exact time of importation into England is clouded by the confusion that existed among the potato, the sweet potato, and other tuber- and root-forming plants. In 1586, Sir Francis Drake introduced into England a plant that he incorrectly called potato. On this trip, Drake had stopped in Virginia and picked up survivors of Raleigh's Colony on Roanoke Island. Heriot. one of the colonists Drake brought back to England, later became farm manager of an estate in Ireland owned by Sir Walter Raleigh. However, the tubers or roots Heriot took back to England could not have been potatoes because none of his written descriptions of six root- or tuber-forming plants even approximates the potato.

It could very well be that the Spaniards first brought the crop to Ireland, because trade was brisk between Spain and Ireland in the 17th century. Without question, the newly introduced plant first became an important agricultural crop in Ireland. Soon after its introduction there, the potato was readily accepted as a staple food, demonstrating for the first time the potential commercial value of a plant that previously was not more than a botanical curiosity. Between 1650 and 1840 potatoes had become a vital part of the basic food supply in Ireland. When late blight disease wiped out the crop in the 1840's, famine forced many Irish people to emigrate to America. Because of its early food use and importance in Ireland, the potato plant is sometimes erroneously called the Irish potato.

When or where the potato was introduced into the continental United States is not known. It is believed that potatoes did not exist in Virginia when Drake landed there in 1586; if he had potatoes aboard his flagship, it is thought that they came from Cartagena (Colombia). One of the early colonial records shows that potatoes were ordered to be taken from England to South Carolina by colonists settling on the Edisto River in 1674. There is no record that potatoes were actually introduced at the time, however. Potatoes were introduced from Ireland into Londonderry, NH in 1719, by a group of Presbyterian Irish. This is the first introduction into New England and possibly into the United States. Acceptance of potatoes as food was very slow in North America. However, total production had reached 1,603,730 cwt (728,100 metric tons) in 1840, when potatoes were first mentioned in the U.S. Census.

The potato industry in Canada dated back to 1623, when a small patch was grown at Port Royal (now Annapolis Royal) in Nova Scotia. The captain of an English trading ship had presented a barrel of potatoes to the early Acadian settlers, who used some of the potatoes for planting. From this humble beginning the potato has become one of the most important Canadian crops and is grown on more farms and in more gardens than any other food plant.

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Botany of the Potato

The potato is one of about 2,000 species in the family Solanaceae. This family includes such plants as tobacco, tomato, eggplant, pepper, horse nettle, bittersweet, ground cherry, and petunia. Botanically, the potato cultivated in North America, Europe, and other lands is Solarium tuberosum L. There are nearly 160 wild species and 20 cultivated species of the tuber-bearing Solanums. All these relatives of the potato are of New World origin. Probably the closest wild relative is S. andigenum Juz & Buk, which produces acceptable yields under the short-day conditions of the Andes Mountains. Most botanists now consider S. andigenum to be a subspecies of S. tuberosum.

The potato may be classified as a dicotyledonous annual, although it can persist in the field vegetatively (as tubers) from one season to the next. In fact, volunteer plants growing from unharvested potato tubers, unintentionally left in the field, create many problems in pest management that affect the production of certified seed as well as that of commercial potatoes.

Being a dicotyledonous plant, the potato has the characteristics of all dicotyledons including stems with vascular bundles placed in a circular arrangement and containing definite layers of xylem and phloem. The potato may be grafted within the species Solanum tuberosum as well as upon related species. Frequently one reads of tomatoes being grafted upon potato root stocks to obtain plants bearing tomatoes on the tops and potatoes underground. Such plants have no commercial value. Some potato breeders have grafted varieties of potatoes upon tomato stocks (or vice versa) to induce better flowering and seed setting and for disease studies.

Morphology and Anatomy

The buds (eyes), are found in a spiral pattern on the tuber. The eyes tend to be concentrated at the seed or apical end of the tuber. They are fewer in number and farther apart toward the stem end where the tuber is attached to the stolon.

The buds (eyes) of the seed end possess apical dominance and will normally sprout first, a condition characteristic of buds at or near the apex of all conventional stems. When the apical buds are removed, or die, other buds are stimulated to sprout in the same manner as lateral buds on a woody stem are stimulated to sprout when the "leader" is removed. When whole tubers are planted, generally the buds near the apex will develop. The effect of apical dominance is reduced if a large tuber is cut into smaller seed pieces. There is a noticeable difference in the rate of emergence between stem-end and seed-end sprouts.

The outer layer of single cells of the tuber, the epidermis. is usually colorless. Anthocyanin, the pigment that colors red and blue potatoes, is found in the periderm (several layers of corky cells immediately below the epidermis). The corky epidermis and periderm together comprises the "skin" of the mature tuber (Fig. 1). The varieties Norland, Chieftain, Red La Soda, LaRouge, Pontiac, and Viking are commercial varieties with red pigment (anthocyanin) in the periderm. In a few varieties the colored pigment is in the outer layers of the cortex, the region immediately inside the periderm that extends inwardly to the vascular ring. Varieties known to have red pigment in the outer cortex are Spaulding Rose, Early Rose, and Early Ohio.

FIGURE 1. Cross section of a potato tuber. The water-soaked appearance of the inner medulla is normal though it may be more pronounced in some tubers than in others.

The remainder of the tuber from the vascular ring inward, designated as the medullary area, is divided into outer and inner medulla and constitutes the fleshy part of the tuber. The outer medulla generally contains the denser portion of this area; the inner medulla includes the watery and more translucent part. Persons unfamiliar with the internal structure of the potato sometimes mistake the inner medulla for an abnormality or defect. The inner medulla extends toward each eye, forming a continuous tissue that connects all the eyes of the tuber (Fig. 1).

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The initiation of young tubers at the tips of the stolons usually occurs when the plants are 6 to 8 inches (15 to 20cm) high, or from 5 to 7 weeks after planting (Fig. 2). Tuberization is affected by many environmental factors and depends largely on translocation and storage of food in excess of that needed by other parts of the plant in its growth and metabolism. Growth of the young tuber is the result of both cell division and elongation and storage of translocated food constituents within the cells.

FIGURE 2. Diagrammatic drawing of the potato plant. Note that tubers are formed on stolons and that stolons differ from roots.

Contrary to a commonly accepted notion, tuberization is not dependent upon flowering. Potato plants will form tubers without any flowers ever appearing on the tops. Some researchers have suggested that tuberization is actually enhanced by removing the flowers or flower buds. The notion that tuberization depends on flowering arose because unfavorable climate such as hot and dry growing conditions, which are normally unfavorable for flowering, also retard or even inhibit tuber formation. Because climatic conditions that favor flowering also favor tuberization, it seems natural to make the mistake of associating flowering with high yields and poor flowering with low yields.

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Plant Introduction and Maintenance

In 1851, C.E. Goodrich, a clergyman of Utica, NY, introduced a small amount of potatoes received from the American consulate in Panama. One of them, Rough Purple Chili, was one of the most valuable plant introductions in history and continues to have a tremendous impact on the North American potato industry. It contributed 100% of the pedigree of the main U.S. potato variety, Russet Burbank, and an average of about 25% of the pedigrees of the ten most important varieties grown in North America.

Since 1925, plant exploration trips have been made into Mexico, Central America and South America, where the potato originated, in search of new forms of the potato for use in improving commercial types. In addition, many named varieties of potato have been introduced into North America as parental material from most of the potato-producing areas of the world. The continual flow of new material coming into the U.S. is coordinated by the U. S. Department of Agriculture. New material coming into Canada under quarantine regulations is handled by the Central Plant Health Laboratory of Agriculture Canada.

Potato introductions and their exploitation are especially important because: 1) The potato is the most economically important vegetable in the U. S. and the world, 2) There is a broad array of easily accessible related germplasm, 3) Solutions to most of the present limitations of the potato have been demonstrated to exist in related germplasm, and 4) Potato has a great potential to provide nutritious food in diversity of environments for an increasingly hungry world.

A diverse genetic pool of tuber bearing Solarium species is maintained at the Inter-regional Potato Introduction Station at Sturgeon Bay, Wisconsin (supported by the USDA and the University of Wisconsin) and by Agriculture Canada. Because of the difficulty of maintaining vegetatively propagated stock disease- and insect-free, much of the genetic base is maintained as true seed. Clones that have some particular significance as an intact genotype are maintained via sterile in vitro culture.

Potato Consumption

Educational efforts by the potato industry have improved the image of the potato in the eyes of consumers. Potatoes are now recognized for their nutritional value. Formerly, it was commonly believed that potatoes were fattening.

Potato consumption in the U.S. prior to the 1950's reflects the negative attitude surrounding potatoes. Per capita consumption reached its low point during the 1950's, averaging 107 pounds (49 kg) per person. By the 1980's per capita consumption had improved to 121 pounds (55 kg), an improvement of about 14 pounds (6 kg) per person.

While total consumption has been increasing, consumers continue to adjust consumption by product form. Fresh per capita consumption continued to decline until the late 1970's and stabilized at between 45-50 pounds (20-23 kg) during the 1980's (Table 3). The year to year fluctuations were caused by variations in crop size.

Table 3. Potatoes: Production per capita consumption in the United States and Canada.

Sources: 1946-1990. World Supply and Demand Situation, ERS, USDA Handbook of Food Expenditures, Prices, and Consumption. Agriculture Canada Cat. #A73-5276, 1990.

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The decline in fresh consumption has been more than offset by a steady growth in consumption of processed products. During the 30-year period from 1960 to 1989 (Table 3), consumption of processed products, on a farm-weight basis, tripled. Most of that growth is attributable to frozen products. In 1960, per capita consumption of frozen products was 6.6 pounds (3 kg). By 1989, that increased to 46 pounds (21 kg). The 34 pound (15 kg) difference in fresh consumption between 1960 and 1989 was more than offset by the 39.5 pound (18 kg) increase in the use of frozen products. Per capita consumption of chips also improved significantly from 11.6 pounds (5 kg) in 1960 to 17.8 pounds (8 kg) in 1989, an increase of about 50 percent.

Use of dehydrated potatoes grew significantly between 1960 and the mid 1970's. Since that time, consumption declined and then stabilized at about 10 pounds (4.5 kg). Consumption of canned potatoes has also shown improvement, but is a very small part of the total potato market.

The shifts in consumption, shown in Table 3, are the result of a number of factors. Some of these factors are the changing structure of the U.S. household, increased focus on health, and the increased availability of fresh fruits and vegetables throughout the year.

The structural shifts in U.S. households have had a major impact on potato consumption. Household size has been declining. Fresh potato consumption has long been heavily influenced by household size where the higher the number of household members the greater the consumption of fresh potatoes. While this pattern may still be true, the decline in the number of large households has a negative effect on total fresh consumption.

The increasing number of households with two or more members employed outside the household also has affected consumption patterns. Outside employment has reduced the amount of time available for food preparation. Traditional dishes which require significant amounts of time for preparation are seldom served. Processed products are filling this need with minimum preparation time. The advent of microwave ovens may have been a major factor in stemming the decline in fresh consumption.

Table 3 also contains Canadian per capita consumption data. The long-term trends in total consumption are not apparent in these data. What is apparent is the higher capita consumption in Canada compared with the U.S. Any long-term trends are hidden by the wide fluctuation in consumption levels from year to year.

The Potato as Food

The potato has spelled survival for millions during the last three centuries. For many people--from South America to Europe--daily servings of potatoes, supplemented with small amounts of milk, meat and fish, have been the cornerstone of a life-giving diet. But many are unaware of how important a contribution relatively small amounts of potatoes still make to North American nutrition today.

The key to this contribution is what modern nutritionists call the high "nutrient density" of the potato. This means simply that, for each calorie of potato eaten, there is an ample return of essential nutritional values.

To see the potato as nutritionists see it, consider that the per capita consumption averages only a little more than 100 calories a day, about four to five percent of most adults' total food. Yet, for example, this small amount (roughly equal to a potato about 2.5 inches (6.4 cm) in diameter) provides the majority of the needed Vitamin C, See Table 4.

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Table 4. Nutritional composition of a medium sized potato (about 1/3 pound or 150 g).

So the four to five percent of the calories that come from potatoes furnish at least 50% of U.S. recommendations for Vitamin C. Moreover, these standards are high. A small daily potato can supply the whole body's need of Vitamin C for most people. In fact, if we had no Vitamin C except for that from potatoes, on a per capita basis, there would be no sign of scurvy (Vitamin C deficiency disease) in the U.S.

The extreme density of Vitamin C in potatoes is not equaled by its other nutrients, but at least 12 essential vitamins and minerals are furnished, plus protein in amounts greater than or equal to its percentage contribution of calories consumed. Potatoes are also an excellent source of dietary fiber.

The nutritional values were established from data obtained through a multi-university study sponsored by The National Potato Board and later verified through a "market basket" survey in 1978.

These values were obtained through averaging, but skewed toward the low end to better assure that an average potato would yield at a minimum the amounts shown. The values also now serve as a national nutritional label for potatoes.

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Why is the Nutrient Density of Potatoes Important?

A key problem of human nutrient in North America is that the need for calories is down at least a third from 1900 because physical activity is lower. Yet, there is a need for the same nutrition from our lessened calories needs.

So, unless, nutrient-dense foods are eaten, too many calories are consumed in getting adequate nutrition, a main reason for obesity. The alternative is to control calories and get too few nutrients, a common situation.

For example, iron is low in the diets of many children, younger women and the elderly. The potato is not rich in iron; few foods are. Yet consider that potatoes, on a per capita basis in the U.S., supply only two weeks for our average annual calories, but furnish the needed iron for almost a month of the year.

Similarly, folic acid is low in many diets, especially among pregnant women, and it is scarce in foods. Potatoes supply about a month's requirement for folic acid, per capita, each year.

Many of us are short in Vitamin B6. Potatoes furnish about a month and a halfs recommendation for this vitamin. They offer even more of our thiamin, another marginal vitamin, and probably a still larger part of the recommended copper. Through such comparisons of calories to nutrients, one can see why nutrient-dense foods are being commended to the public by nutritionists.

Potatoes and the New Balance of the Diet.

Concern about diet and heart disease has alerted consumers to the high intake of fats--perhaps 45% of our calories and more. Unsuspected by many, this increase is often associated with efforts to eat more protein. But even among deprived populations, U.S. protein consumption tends to be excessive. And many people do not realize that fat tends to be high in "high-protein" foods.

While the effect of diet on heart disease is still unclear, nutritionists have other reasons to suggest lowering fat intake and eating more complex carbohydrate foods. One reason is that fats have more than twice as many calories as do carbohydrates. So many carbohydrate foods have higher nutrient density.

This higher density is not true of all such foods. For example, sweeteners--such as table sugar, honey, corn syrup--are carbohydrates, but have few, if any, other nutrients. Thus, balancing the diet has come to mean cutting back on proteins, fats and sweeteners and increasing nutrient-dense complex carbohydrates.

Potatoes and the Nutrition Future

Nutritionists' interest in nutrient-dense foods which have wide acceptance and low price suggest a renewed appreciation of potatoes. The market has already reflected some of this change.

Studies indicate that most North Americans have overcome old, unscientific prejudices that potatoes are especially caloric, hence, especially fattening. As new analyses explain how potatoes supported life in other, older cultures, as more consumers learn that they need no more protein and that eating much fat tends to mean poor nutrition in societies that spend little body energy, the nutrient-dense potato, a nutritional staple of the past, becomes more and more a food of the future.

Potatoes in a Hungry World

Besides being an important nutrient-dense food, the potato is an efficient producer of food energy and nutrition per unit area and must figure prominently in combating any world food crises. Recent data indicate that potatoes have 75% more food energy per unit area than wheat and 58% more than rice. Also, potatoes have 54% more protein per unit area than wheat and 78% higher than rice. In fact, no other food can match the potato in its production of food energy and food value per unit area.

The potato, a nutritious, delicious, low-cost vegetable is truly a wonder food.

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