From The Plant Encyclopedia
Potato, Potatoes, Potato Vine
3 - 20
- Cultivation: Easy-To-Grow, For-Gardeners
- Light: Sun
- Soil: Rich
- pH: 6, 7, 8
- Moisture: Medium, Well-Drained
- Form: Groundcover, Herbaceous
- Habit: Perennial, Annual
- Flower: Small
- Fruit/Seed: Small
- Foliage: Leaves, Green
- Uses: Edible, Industrial
The potato is a Starchy, Tuberous crop from the perennial Solanum tuberosum of the Solanaceae family (also known as the nightshades). The word potato may refer to the plant itself as well as the edible tuber. In the region of the Andes, there are some other closely related cultivated potato species. Potatoes were first introduced outside the Andes region four centuries ago, and have become an integral part of much of the world's cuisine. It is the world's fourth-largest food crop, following Rice, Wheat, and Maize. Long-term storage of potatoes requires specialised care in cold warehouses.
Wild potato species occur throughout The Americas, from the United States to Uruguay. The potato was originally believed to have been domesticated independently in multiple locations, but later genetic testing of the wide variety of Cultivars and wild species proved a single origin for potatoes in the area of present-day southern Peru (from a species in the Solanum brevicaule complex), where they were domesticated 7,000–10,000 years ago. Following centuries of Selective breeding, there are now over a thousand different types of potatoes. Of these Subspecies, a variety that at one point grew in the Chiloé Archipelago (the potato's south-central Chilean sub-center of origin) left its Germplasm on over 99% of the cultivated potatoes worldwide.
There are over 4000 different varieties of potato, it has been bred into many standard or well-known varieties, each of which has particular agricultural or culinary attributes. In general, varieties are categorized into a few main groups, such as russets, reds, whites, yellows (also called Yukons) and purples—based on common characteristics. Around 80 varieties are commercially available in the UK. For culinary purposes, varieties are often described in terms of their waxiness. Floury, or mealy (baking) potatoes have more starch (20–22%) than waxy (boiling) potatoes (16–18%). The distinction may also arise from variation in the comparative ratio of two potato starch compounds: Amylose and Amylopectin. Amylose, a long-chain molecule, diffuses out of the starch granule when cooked in water, and lends itself to dishes where the potato is mashed. Varieties that contain a slightly higher amylopectin content, a highly branched molecule, help the potato retain its shape when boiled.
The European Cultivated Potato Database (ECPD) is an online collaborative database of potato variety descriptions, updated and maintained by the Scottish Agricultural Science Agency within the framework of the European Cooperative Programme for Crop Genetic Resources Networks (ECP/GR)—which is organised by the International Plant Genetic Resources Institute (IPGRI).
There are approximately 500 varieties of Potato that are commonly grown in gardens.
Following the Spanish conquest of the Inca Empire, the Spanish introduced the potato to Europe in the second half of the 16th century. The staple was subsequently conveyed by European mariners to territories and ports throughout the world. The potato was slow to be adopted by distrustful European farmers, but soon enough it became an important food staple and field crop that played a major role in the European 19th century population boom. However, lack of genetic diversity, due to the very limited number of varieties initially introduced, left the crop vulnerable to disease. In 1845, a plant disease known as late blight, caused by the fungus-like Oomycete Phytophthora infestans, spread rapidly through the poorer communities of western Ireland, resulting in the crop failures that led to the Great Irish Famine. Nonetheless, thousands of varieties persist in the Andes, where over 100 cultivars might be found in a single valley, and a dozen or more might be maintained by a single agricultural household.
The annual diet of an average global citizen in the first decade of the 21st century included about of potato. However, the local importance of potato is extremely variable and rapidly changing. It remains an essential crop in Europe (especially eastern and central Europe), where per capita production is still the highest in the world, but the most rapid expansion over the past few decades has occurred in southern and eastern Asia. China is now the world's largest potato-producing country, and nearly a third of the world's potatoes are harvested in China and India.
Potato plants are herbaceous Perennials that grow about 60 cm (24 in) high, depending on variety, the culms dying back after flowering. They bear white, pink, red, blue, or purple Flowers with yellow Stamens. In general, the tubers of varieties with white flowers have white skins, while those of varieties with colored flowers tend to have pinkish skins. Potatoes are cross-pollinated mostly by Insects, including Bumblebees, which carry pollen from other potato plants, but a substantial amount of self-fertilizing occurs as well. Tubers form in response to decreasing day length, although this tendency has been minimized in commercial varieties. After potato plants flower, some varieties produce small green fruits that resemble green Cherry tomatoes, each containing up to 300 true Seeds. Potato fruit contains large amounts of the toxic Alkaloid Solanine and is therefore unsuitable for consumption. All new potato varieties are grown from seeds, also called "true seed" or "botanical seed" to distinguish it from seed tubers. By finely chopping the fruit and soaking it in water, the seeds separate from the flesh by sinking to the bottom after about a day (the remnants of the fruit float). Any potato variety can also be propagated vegetatively by planting tubers, pieces of tubers, cut to include at least one or two eyes, or also by cuttings, a practice used in greenhouses for the production of healthy seed tubers. Some commercial potato varieties do not produce Seeds at all (they bear imperfect flowers) and are propagated only from tuber pieces. Confusingly, these tubers or tuber pieces are called "seed potatoes".
Growth and cultivation
Potato growth has been divided into five phases. During the first phase, sprouts emerge and root growth begins. During the second, Photosynthesis begins as the plant develops leaves and branches. New tubers develop during the third phase, which is often (but not always) associated with flowering. Tuber formation halts when soil temperatures reach ; hence potatoes are considered a cool-season crop. Tuber bulking occurs during the fourth phase, when the plant begins investing the majority of its resources in its newly formed tubers. At this stage, several factors are critical to yield: optimal soil moisture and temperature, soil nutrient availability and balance, and resistance to pest attacks. The final phase is maturation: The plant canopy dies back, the tuber skins harden, and their sugars convert to starches.
New tubers may arise at the soil surface. Since exposure to light leads to greening of the skins and the development of solanine, growers are interested in covering such tubers. Commercial growers usually address this problem by piling additional soil around the base of the plant as it grows ("hilling", or in British English "earthing up"). An alternative method used by home gardeners and smaller-scale growers involves covering the growing area with organic Mulches such as straw or with plastic sheets.
Correct potato husbandry can be an arduous task in some circumstances. Good ground preparation, Harrowing, plowing, and rolling are always needed, along with a little grace from the weather and a good source of water. Three successive plowings, with associated harrowing and rolling, are desirable before planting. Eliminating all root-weeds is desirable in potato cultivation. In general, the potatoes themselves are grown from the eyes of another potato and not from seed. Home gardeners often plant a piece of potato with two or three eyes in a hill of mounded soil. Commercial growers plant potatoes as a row crop using seed tubers, young plants or microtubers and may mound the entire row. Seed potato crops are 'rogued' in some countries to eliminate diseased plants or those of a different variety from the seed crop.
Potatoes are sensitive to heavy Frosts, which damage them in the ground. Even cold weather makes potatoes more susceptible to bruising and possibly later rotting, which can quickly ruin a large stored crop.
At harvest time, gardeners usually dig up potatoes with a long-handled, three-prong "grape" (or graip), i.e., a Spading fork, or a potato hook, which is similar to the graip but with tines at a 90 degree angle to the handle. In larger plots, the plow is the fastest implement for unearthing potatoes. Commercial harvesting is typically done with large potato harvesters, which scoop up the plant and surrounding earth. This is transported up an apron chain consisting of steel links several feet wide, which separates some of the dirt. The chain deposits into an area where further separation occurs. Different designs use different systems at this point. The most complex designs use vine choppers and shakers, along with a blower system or "Flying Willard" to separate the potatoes from the plant. The result is then usually run past workers who continue to sort out plant material, stones, and rotten potatoes before the potatoes are continuously delivered to a wagon or truck. Further inspection and separation occurs when the potatoes are unloaded from the field vehicles and put into storage.
Immature potatoes may be sold as "New Potatoes" and are particularly valued for taste. These are often harvested by the home gardener or farmer by "grabbling", i.e. pulling out the young tubers by hand while leaving the plant in place.
Potatoes are usually cured after harvest to improve skin-set. Skin-set is the process by which the skin of the potato becomes resistant to skinning damage. Potato tubers may be susceptible to skinning at harvest and suffer skinning damage during harvest and handling operations. Curing allows the skin to fully set and any wounds to heal. Wound-healing prevents infection and water-loss from the tubers during storage. Curing is normally done at relatively warm temperatures to with high humidity and good gas-exchange if at all possible.
Storage facilities need to be carefully designed to keep the potatoes alive and slow the natural process of decomposition, which involves the breakdown of starch. It is crucial that the storage area is dark, well ventilated and for long-term storage maintained at temperatures near . For short-term storage before cooking, temperatures of about to are preferred.
On the other hand, temperatures below convert potatoes' starch into sugar, which alters their taste and cooking qualities and leads to higher Acrylamide levels in the cooked product, especially in deep-fried dishesthe discovery of acrylamides in starchy foods in 2002 has led to many international health concerns as they are believed to be possible carcinogens and their occurrence in cooked foods are currently under study as possible influences in potential health problems.
Under optimum conditions possible in commercial warehouses, potatoes can be stored for up to ten to twelve months. When stored in homes, the shelf life is usually only a few weeks. If potatoes develop green areas or start to sprout, these areas should be trimmed before using.
Commercial storage of potatoes involves several phases: drying of surface moisture; a wound healing phase at 85% to 95% Relative humidity and temperatures below ; a staged cooling phase; a holding phase; and a reconditioning phase, during which the tubers are slowly warmed. Mechanical ventilation is used at various points during the process to prevent condensation and accumulation of Carbon dioxide.
When stored in the home, mature potatoes are optimally kept at room temperature, where they last 1 to 2 weeks in a paper bag, in a dry, cool, dark, well ventilated location. If mature potatoes are refrigerated, dark spots can occur and conversion of starch into sugar can give rise to an unpleasant sweet flavour when cooked. Only new potatoes can be refrigerated, and should be kept so, where they have a shelf life of 1 week. If kept in too warm a temperature, both mature and new potatoes will sprout and shrivel. Exposure to light causes them to turn green. Also, potatoes absorb odours produced by Pears.
The major species grown worldwide is Solanum tuberosum (a Tetraploid with 48 Chromosomes), and modern varieties of this species are the most widely cultivated. There are also four diploid species (with 24 chromosomes): S. stenotomum, S. phureja, S. goniocalyx, and S. ajanhuiri. There are two triploid species (with 36 chromosomes): S. chaucha and S. juzepczukii. There is one pentaploid cultivated species (with 60 chromosomes): S. curtilobum.
There are two major subspecies of Solanum tuberosum: andigena, or Andean; and tuberosum, or Chilean. The Andean potato is adapted to the short-day conditions prevalent in the mountainous equatorial and tropical regions where it originated. The Chilean potato is adapted to the long-day conditions prevalent in the higher latitude region of southern Chile, especially on Chiloé Archipelago where it is thought to have originated. Genetic testing done in 2005 showed that both subspecies derive from a common ancestor from the area of southern Peru.
There are about five thousand potato varieties worldwide. Three thousand of them are found in the Andes alone, mainly in Peru, Bolivia, Ecuador, Chile, and Colombia. They belong to eight or nine species, depending on the taxonomic school. Apart from the five thousand cultivated varieties, there are about 200 wild species and subspecies, many of which can be cross-bred with cultivated varieties, which has been done repeatedly to transfer resistances to certain pests and diseases from the gene pool of wild species to the gene pool of cultivated potato species. Genetically modified varieties have met public resistance in the United States and in the European Union.
Most modern potatoes grown in North America arrived through European settlement and not independently from the South American sources. However, at least one wild potato species, Solanum fendleri, is found as far north as Texas and used in breeding for resistance to a Nematode species that attacks cultivated potatoes. A secondary center of genetic variability of the potato is Mexico, where important wild species that have been used extensively in modern breeding are found, such as the hexaploid Solanum demissum, as a source of resistance to the devastating late blight disease. Another relative native to this region, Solanum bulbocastanum, has been used to genetically engineer the potato to resist potato blight.
The International Potato Center, based in Lima, Peru, holds an ISO-accredited collection of potato Germplasm.
Potatoes yield abundantly with little effort, and adapt readily to diverse climates as long as the climate is cool and moist enough for the plants to gather sufficient water from the soil to form the starchy tubers. Potatoes do not keep very well in storage and are vulnerable to molds that feed on the stored tubers, quickly turning them rotten. By contrast, grain can be stored for several years without much risk of rotting.
The international Potato Genome Sequencing Consortium announced in 2009 that they had achieved a draft sequence of the potato genome. The potato genome contains 12 chromosomes and 860 million base pairs making it a medium-sized plant genome.
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Sailors returning from Peru to Spain with silver presumably brought maize and potatoes for their own food on the trip. Historians speculate that leftover tubers (and maize) were carried ashore and planted: "We think that the potato arrived some years before the end of the 16th century, by two different ports of entry: the first, logically, in Spain around 1570, and the second via the British isles between 1588 and 1593 ... we find traces of the transport of potatoes travelling from the Canaries to Antwerp in 1567 ... we can say that the potato was introduced there [the Canary islands] from South America around 1562 ... the first written mention of the potato [is] ... a receipt for delivery dated 28 november 1567 between Las Palmas in the Grand Canaries and Antwerp." Basque fishermen from Spain used potatoes as ships stores for their voyages across the Atlantic in the 16th century, and introduced the tuber to western Ireland, where they landed to dry their cod. In 1553, in the book Crónica del Peru, Pedro Cieza de Leon mentions he saw it in Quito, Popayán, and Pasto in 1538. The English privateer Francis Drake, returning from his circumnavigation, or Sir Walter Raleigh's employee Thomas Harriot are commonly credited with introducing potatoes into England. In 1588, botanist Carolus Clusius made a painting of what he called "Papas Peruanorum" from a specimen in Belgium; in 1601 he reported that potatoes were in common use in northern Italy for animal fodder and for human consumption.
The Spanish had an empire across Europe, and brought potatoes for their armies. Peasants along the way adopted the crop, which was less often pillaged by marauding armies than above-ground stores of grain. Across most of northern Europe, where open fields prevailed, potatoes were strictly confined to small garden plots because field agriculture was strictly governed by custom that prescribed seasonal rhythms for plowing, sowing, harvesting and grazing animals on fallow and stubble. This meant that potatoes were barred from large-scale cultivation because the rules allowed only grain to be planted in the open fields. In France and Germany government officials and noble landowners promoted the rapid conversion of fallow land into potato fields after 1750. The potato thus became an important Staple crop in northern Europe. Famines in the early 1770s contributed to its acceptance, as did government policies in several European countries and climate change during the Little Ice Age, when traditional crops in this region did not produce as reliably as before. At times when and where most other crops failed, potatoes could still typically be relied upon to contribute adequately to food supplies during colder years.
In France " At the end of the 16th century, the potato had not only been introduced in the Franche-Comté ... equally in the Vosges of Lorraine, probably coming from Alsace. It spread greatly there in the middle of the 17th century ... Some authors also remark its introduction from England into Flanders during the wars against Louis XIV ... In the 18th century ... Some instructions to cultivators spread by the Agricultural Bureaus contribute to the potato's development ... To such a point that in the 1785 edition of the 'Bon Jardinier' it is written: 'There is no vegetable about which so much has been written and so much enthusiasm has been shown ... The poor should be quite content with this foodstuff' ... in 1758 in Saint-Dié(Vosges) a production of about 2,000 tons was realized" It had widely replaced the Turnip and Rutabaga by the 19th century.
19th century EuropeFrench physician Antoine Parmentier studied the potato intensely and in Examen chymique des pommes de terres (Paris, 1774) showed their enormous nutritional value. King Louis XVI and his court eagerly promoted the new crop, with Queen Marie Antoinette even wearing a headdress of potato flowers at a fancy dress ball. The annual potato crop of France soared to 21 million hectoliters in 1815 and 117 million in 1840, allowing a concomitant growth in population while avoiding the Malthusian trap. Although potatoes had become widely familiar in Russia by 1800, they were confined to garden plots until the grain failure in 1838–1839 persuaded peasants and landlords in central and northern Russia to devote their fallow fields to raising potatoes. Potatoes yielded from two to four times more calories per acre than grain did, and eventually came to dominate the food supply in eastern Europe. Boiled or baked potatoes were cheaper than rye bread, just as nutritious, and did not require a gristmill for grinding. On the other hand cash-oriented landlords realized that grain was much easier to ship, store and sell, so both grain and potatoes coexisted.
Throughout Europe, the most important new food in the 19th century was the potato, which had three major advantages over other foods for the consumer: its lower rate of spoilage, its bulk (which easily satisfied hunger), and its cheapness. The crop slowly spread across Europe, such that, for example, by 1845 it occupied one-third of Irish arable land. Potatoes comprised about 10% of the caloric intake of Europeans. Along with several other foods that either originated in the Americas or were successfully grown or harvested there, potatoes sustained European populations.
In Britain, the potato promoted economic development by underpinning the Industrial Revolution in the 19th century. It served as a cheap source of calories and nutrients that was easy for urban workers to cultivate on small backyard plots. Potatoes became popular in the north of England, where coal was readily available, so a potato-driven population boom provided ample workers for the new factories. Marxist Friedrich Engels even declared that the potato was the equal of iron for its "historically revolutionary role. The Dutch potato-starch industry grew rapidly in the 19th century, especially under the leadership of entrepreneur Willem Albert Scholten (1819–92).
In Ireland, the expansion of potato cultivation was due entirely to the landless laborers, renting tiny plots from landowners, who were interested only in raising cattle or in producing grain for market. A single acre of potatoes and the milk of a single cow was enough to feed a whole Irish family a monotonous but nutritionally adequate diet for a healthy, vigorous (and desperately poor) rural population. Often even poor families grew enough extra potatoes to feed a pig that they could sell for cash.
A lack of genetic diversity from the low number of varieties left the crop vulnerable to disease. In 1845, a plant disease known as late blight, caused by the fungus-like Oomycete Phytophthora infestans, spread rapidly through the poorer communities of western Ireland, resulting in the crop failures that led to the Great Irish Famine.
The Lumper potato, widely cultivated in western and southern Ireland before and during the great famine, was bland, wet, and poorly resistant to the potato blight, but yielded large crops and usually provided adequate calories for peasants and laborers. Heavy dependence on this potato led to disaster when the potato blight turned a newly harvested potato into a putrid mush in minutes. The Irish Famine in the western and southern parts of the British-controlled island of Ireland, 1845–49, was a catastrophic failure in the food supply that led to approximately a million deaths from famine and (especially) diseases that attacked weakened bodies, and to massive emigration to Britain, the U.S. and Canada.
Canary Islands Study
Shipping records from 1567 make the Canary Islands islands off the shores northwest Africa the first known home to potatoes outside of Central and South America. In 2007, David Spooner, a horticulturist with the U.S. Department of Agriculture and a researcher at the University of Wisconsin, Madison, decided to analyze potatoes on the island. He found that some potatoes on the Canary Islands had genetic markers of Andean origins and some had markers indicating Chilean roots. Two subspecies of these wild spuds, one found in Chile, the other in the Andean highlands of Peru, look very similar but differ genetically. Most scientists have long assumed that European potatoes, the foundation for all modern cultivated potatoes, come from the Chilean variety, because Chilean lowlands resemble Europe's environment most closely. According to Spooner, "The idea that it was a single introduction from Chile just doesn't stand up". Spooner suggests that different varieties could have been brought from South America at various times.
It is generally believed that Potatoes also entered Africa with colonists, who consumed them as a vegetable rather than as a staple starch. Shipping records from 1567 make the Canary Islands islands off the shores northwest Africa the first known home to potatoes outside of Central and South America though. Like in other continents, in spite of its advantages as an antifamine, high-elevation alternative to grain, the potato was at first resisted by local farmers who thought it was poisonous. The colonialists also promoted it as a low cost food to them and so it was a symbol of domination. In former European colonies of Africa, potatoes were initially consumed only occasionally, but increased production made them a staple in certain areas. In Africa, as in Europe, the popularity of the tubers increased in wartime because they could be stored in the ground.
In present day Africa it has been a vegetable or co-staple crop.
The potato contains Vitamins and minerals, as well as an assortment of Phytochemicals, such as Carotenoids and natural phenols. Chlorogenic acid constitutes up to 90% of the potato tuber natural phenols. Others found in potatoes are 4-O-caffeoylquinic (crypto-chlorogenic acid), 5-O-caffeoylquinic (neo-chlorogenic acid), 3,4-dicaffeoylquinic and 3,5-dicaffeoylquinic acids. A medium-size 150 g (5.3 oz) potato with the skin provides 27 mg of Vitamin C (45% of the Daily Value (DV)), 620 mg of Potassium (18% of DV), 0.2 mg vitamin B6 (10% of DV) and trace amounts of Thiamin, Riboflavin, Folate, Niacin, Magnesium, Phosphorus, iron, and zinc. The fiber content of a potato with skin (2 g) is equivalent to that of many whole grain Breads, Pastas, and Cereals.
In terms of nutrition, the potato is best known for its Carbohydrate content (approximately 26 grams in a medium potato). The predominant form of this carbohydrate is Starch. A small but significant portion of this starch is resistant to digestion by Enzymes in the Stomach and Small intestine, and so reaches the Large intestine essentially intact. This Resistant starch is considered to have similar physiological effects and health benefits as fiber: It provides bulk, offers protection against Colon cancer, improves Glucose tolerance and insulin sensitivity, lowers plasma cholesterol and Triglyceride concentrations, increases satiety, and possibly even reduces fat storage. The amount of resistant starch in potatoes depends much on preparation methods. Cooking and then cooling potatoes significantly increases resistant starch. For example, cooked Potato starch contains about 7% resistant starch, which increases to about 13% upon cooling.
The nutrients of the potato seem to be fairly evenly distributed between the flesh and the skin. For a medium potato, with and without the skin, nutritiondata.com gives the following:
|Nutrient||Without skin (156 g) (% RDA)||With skin (173 g) (% RDA)|
The cooking method used can significantly impact the nutrient availability of the potato.
Potatoes are often broadly classified as high on the Glycemic index (GI) and so are often excluded from the diets of individuals trying to follow a low-GI diet. In fact, the GI of potatoes can vary considerably depending on type (such as red, russet, white, or Prince Edward), origin (where it was grown), preparation methods (i.e., cooking method, whether it is eaten hot or cold, whether it is mashed or cubed or consumed whole, etc.), and with what it is consumed (i.e., the addition of various high-fat or high-protein toppings).
Potatoes are not considered by the NHS as counting towards the five portions of fruit and vegetables diet.
These compounds, which protect the plant from its predators, are, in general, concentrated in its leaves, stems, sprouts, and fruits. Exposure to light, physical damage, and age increase glycoalkaloid content within the tuber; the highest concentrations occur just underneath the skin. Cooking at high temperatures (over 170 °C or 340 °F) partly destroys these. The concentration of glycoalkaloid in wild potatoes suffices to produce toxic effects in humans. Glycoalkaloids may cause Headaches, Diarrhea, Cramps, and in severe cases Coma and death; however, poisoning from potatoes occurs very rarely. Light exposure causes greening from Chlorophyll synthesis, thus giving a visual clue as to areas of the tuber that may have become more toxic; however, this does not provide a definitive guide, as greening and glycoalkaloid accumulation can occur independently of each other. Some varieties of potato contain greater glycoalkaloid concentrations than others; breeders developing new varieties test for this, and sometimes have to discard an otherwise promising Cultivar. Breeders try to keep solanine levels below 200 mg/kg (200 ppmw). However, when these commercial varieties turn green, even they can approach concentrations of solanine of 1000 mg/kg (1000 ppmw). In normal potatoes, analysis has shown solanine levels may be as little as 3.5% of the breeders' maximum, with 7–187 mg/kg being found.
The U.S. National Toxicology Program suggests that the average American consume at most 12.5 mg/day of solanine from potatoes (the toxic dose is actually several times this, depending on body weight). Douglas L. Holt, the State Extension Specialist for Food Safety at the University of Missouri, notes that no reported cases of potato-source solanine poisoning have occurred in the U.S. in the last 50 years, and most cases involved eating green potatoes or drinking potato-leaf tea.