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Potato

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Potato
Patates.jpg
Potato cultivars appear in a variety of colors, shapes, and sizes.
Scientific classification edit
Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Eudicots
Clade: Asterids
Order: Solanales
Family: Solanaceae
Genus: Solanum
Species:
S. tuberosum
Binomial name
Solanum tuberosum
Synonyms[1]

The potato is a root vegetable, a starchy tuber of the plant Solanum tuberosum, and the plant itself, a perennial in the family Solanaceae,[2] native to the Americas.

Wild potato species can be found throughout the Americas, from the United States to southern Chile.[3] The potato was originally believed to have been domesticated by indigenous peoples of the Americas independently in multiple locations,[4] but later genetic testing of the wide variety of cultivars and wild species traced a single origin for potatoes. In the area of present-day southern Peru and extreme northwestern Bolivia, from a species in the Solanum brevicaule complex, potatoes were domesticated approximately 7,000–10,000 years ago.[5][6][7] In the Andes region of South America, where the species is indigenous, some close relatives of the potato are cultivated.

Potatoes were introduced to Europe from the Americas in the second half of the 16th century by the Spanish. Today they are a staple food in many parts of the world and an integral part of much of the world's food supply. As of 2014, potatoes were the world's fourth-largest food crop after maize (corn), wheat, and rice.[8]

Following millennia of selective breeding, there are now over 1,000 different types of potatoes.[6] Over 99% of presently cultivated potatoes worldwide descended from varieties that originated in the lowlands of south-central Chile, which have displaced formerly popular varieties from the Andes.[9][10]

The importance of the potato as a food source and culinary ingredient varies by region and is still changing. It remains an essential crop in Europe, especially Northern and Eastern Europe, where per capita production is still the highest in the world, while the most rapid expansion in production over the past few decades has occurred in southern and eastern Asia, with China and India leading the world in overall production as of 2014.

Being a nightshade similar to tomatoes, the vegetative and fruiting parts of the potato contain the toxin solanine and are not fit for human consumption. Normal potato tubers that have been grown and stored properly produce glycoalkaloids in amounts small enough to be negligible to human health, but if green sections of the plant (namely sprouts and skins) are exposed to light, the tuber can accumulate a high enough concentration of glycoalkaloids to affect human health.[11][12]

Etymology

The English word potato comes from Spanish patata (the name used in Spain). The Royal Spanish Academy says the Spanish word is a hybrid of the Taíno batata ('sweet potato') and the Quechua papa ('potato').[13][14] The name originally referred to the sweet potato although the two plants are not closely related. The 16th-century English herbalist John Gerard referred to sweet potatoes as common potatoes, and used the terms bastard potatoes and Virginia potatoes for the species we now call potato.[15] In many of the chronicles detailing agriculture and plants, no distinction is made between the two.[16] Potatoes are occasionally referred to as Irish potatoes or white potatoes in the United States, to distinguish them from sweet potatoes.[15]

The name spud for a small potato comes from the digging of soil (or a hole) prior to the planting of potatoes. The word has an unknown origin and was originally (c. 1440) used as a term for a short knife or dagger, probably related to the Latin spad- a word root meaning 'sword'; compare Spanish espada, English spade and spadroon. It subsequently transferred over to a variety of digging tools. Around 1845, the name transferred to the tuber itself, the first record of this usage being in New Zealand English.[17] The origin of the word spud has erroneously been attributed to an 18th-century activist group dedicated to keeping the potato out of Britain, calling itself The Society for the Prevention of Unwholesome Diet (S.P.U.D.). It was Mario Pei's 1949 The Story of Language that can be blamed for the word's false origin. Pei writes, "the potato, for its part, was in disrepute some centuries ago. Some Englishmen who did not fancy potatoes formed a Society for the Prevention of Unwholesome Diet. The initials of the main words in this title gave rise to spud." Like most other pre-20th century acronymic origins, this is false, and there is no evidence that a Society for the Prevention of Unwholesome Diet ever existed.[18][14]

Characteristics

Flowers of a potato plant
Potato plants

Potato plants are herbaceous perennials that grow about 60 cm (24 in) high, depending on variety, with the leaves dying back after flowering, fruiting and tuber formation. 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.[19] Potatoes are mostly cross-pollinated by insects such as bumblebees, which carry pollen from other potato plants, though 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.[20]

After flowering, potato plants produce small green fruits that resemble green cherry tomatoes, each containing about 300 seeds. Like all parts of the plant except the tubers, the fruit contain the toxic alkaloid solanine and are therefore unsuitable for consumption. All new potato varieties are grown from seeds, also called "true potato seed", "TPS" or "botanical seed" to distinguish it from seed tubers. New varieties grown from seed can be propagated vegetatively by planting tubers, pieces of tubers cut to include at least one or two eyes, or cuttings, a practice used in greenhouses for the production of healthy seed tubers. Plants propagated from tubers are clones of the parent, whereas those propagated from seed produce a range of different varieties.

Genetics

There are about 5,000 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 5,000 cultivated varieties, there are about 200 wild species and subspecies, many of which can be cross-bred with cultivated varieties. Cross-breeding 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.[21][22]

Russet potatoes

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.[23] The Andean potato is adapted to the short-day conditions prevalent in the mountainous equatorial and tropical regions where it originated; the Chilean potato, however, native to the Chiloé Archipelago, is adapted to the long-day conditions prevalent in the higher latitude region of southern Chile.[24]

Organically grown Russet Burbanks

The International Potato Center, based in Lima, Peru, holds an ISO-accredited collection of potato germplasm.[25] The international Potato Genome Sequencing Consortium announced in 2009 that they had achieved a draft sequence of the potato genome.[26] The potato genome contains 12 chromosomes and 860 million base pairs, making it a medium-sized plant genome.[27] More than 99 percent of all current varieties of potatoes currently grown are direct descendants of a subspecies that once grew in the lowlands of south-central Chile.[28] Nonetheless, genetic testing of the wide variety of cultivars and wild species affirms that all potato subspecies derive from a single origin in the area of present-day southern Peru and extreme Northwestern Bolivia (from a species in the Solanum brevicaule complex).[5][6][7] The wild Crop Wild Relatives Prebreeding project encourages the use of wild relatives in breeding programs. Enriching and preserving the gene bank collection to make potatoes adaptive to diverse environmental conditions is seen as a pressing issue due to climate change.[29]

Most modern potatoes grown in North America arrived through European settlement and not independently from the South American sources, although at least one wild potato species, Solanum fendleri, naturally ranges from Peru into Texas, where it is 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.[30] Another relative native to this region, Solanum bulbocastanum, has been used to genetically engineer the potato to resist potato blight.[31]

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 moulds that feed on the stored tubers and quickly turn them rotten, whereas crops such as grain can be stored for several years with a low risk of rot. The yield of Calories per acre (about 9.2 million) is higher than that of maize (7.5 million), rice (7.4 million), wheat (3 million), or soybean (2.8 million).[32]

Varieties

There are close to 4,000 varieties of potato including common commercial varieties, each of which has specific agricultural or culinary attributes.[33] Around 80 varieties are commercially available in the UK.[34] In general, varieties are categorized into a few main groups based on common characteristics, such as russet potatoes (rough brown skin), red potatoes, white potatoes, yellow potatoes (also called Yukon potatoes) and purple potatoes.

For culinary purposes, varieties are often differentiated by 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 different potato starch compounds: amylose and amylopectin. Amylose, a long-chain molecule, diffuses from 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, which is a highly branched molecule, help the potato retain its shape after being boiled in water.[35] Potatoes that are good for making potato chips or potato crisps are sometimes called "chipping potatoes", which means they meet the basic requirements of similar varietal characteristics, being firm, fairly clean, and fairly well-shaped.[36]

The European Cultivated Potato Database (ECPD) is an online collaborative database of potato variety descriptions that is 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 run by the International Plant Genetic Resources Institute (IPGRI).[37]

Pigmentation

Potatoes with different pigmentation
Two dark-skinned potatoes on a white plate. A further potato is cut into sections to show the variety's purple-blue flesh, placed at lower-right on the plate.
Potato variety 'Blue Swede'

Dozens of potato cultivars have been selectively bred specifically for their skin or, more commonly, flesh color, including gold, red, and blue varieties[38] that contain varying amounts of phytochemicals, including carotenoids for gold/yellow or polyphenols for red or blue cultivars.[39] Carotenoid compounds include provitamin A alpha-carotene and beta-carotene, which are converted to the essential nutrient, vitamin A, during digestion. Anthocyanins mainly responsible for red or blue pigmentation in potato cultivars do not have nutritional significance, but are used for visual variety and consumer appeal.[40] Recently, as of 2010, potatoes have also been bioengineered specifically for these pigmentation traits.[41]

Genetically engineered potatoes

Genetic research has produced several genetically modified varieties. 'New Leaf', owned by Monsanto Company, incorporates genes from Bacillus thuringiensis, which confers resistance to the Colorado potato beetle; 'New Leaf Plus' and 'New Leaf Y', approved by US regulatory agencies during the 1990s, also include resistance to viruses. McDonald's, Burger King, Frito-Lay, and Procter & Gamble announced they would not use genetically modified potatoes, and Monsanto published its intent to discontinue the line in March 2001.[42]

Waxy potato varieties produce two main kinds of potato starch, amylose and amylopectin, the latter of which is most industrially useful. BASF developed the Amflora potato, which was modified to express antisense RNA to inactivate the gene for granule bound starch synthase, an enzyme which catalyzes the formation of amylose.[43] Amflora potatoes therefore produce starch consisting almost entirely of amylopectin, and are thus more useful for the starch industry. In 2010, the European Commission cleared the way for 'Amflora' to be grown in the European Union for industrial purposes only—not for food. Nevertheless, under EU rules, individual countries have the right to decide whether they will allow this potato to be grown on their territory. Commercial planting of 'Amflora' was expected in the Czech Republic and Germany in the spring of 2010, and Sweden and the Netherlands in subsequent years.[44] Another GM potato variety developed by BASF is 'Fortuna' which was made resistant to late blight by adding two resistance genes, blb1 and blb2, which originate from the Mexican wild potato Solanum bulbocastanum.[45][46] In October 2011 BASF requested cultivation and marketing approval as a feed and food from the EFSA. In 2012, GMO development in Europe was stopped by BASF.[47][48]

In November 2014, the USDA approved a genetically modified potato developed by J.R. Simplot Company, which contains genetic modifications that prevent bruising and produce less acrylamide when fried than conventional potatoes; the modifications do not cause new proteins to be made, but rather prevent proteins from being made via RNA interference.[49][50][51]

History

The potato was first domesticated in the region of modern-day southern Peru and extreme northwestern Bolivia[5] between 8000 and 5000 BC.[6] It has since spread around the world and become a staple crop in many countries.

The earliest archaeologically verified potato tuber remains have been found at the coastal site of Ancon (central Peru), dating to 2500 BC.[52][53] The most widely cultivated variety, Solanum tuberosum tuberosum, is indigenous to the Chiloé Archipelago, and has been cultivated by the local indigenous people since before the Spanish conquest.[54][55]

According to conservative estimates, the introduction of the potato was responsible for a quarter of the growth in Old World population and urbanization between 1700 and 1900.[56] In the Altiplano, potatoes provided the principal energy source for the Inca civilization, its predecessors, and its Spanish successor. Following the Spanish conquest of the Inca Empire, the Spanish introduced the potato to Europe in the second half of the 16th century, part of the Columbian exchange. The staple was subsequently conveyed by European mariners to territories and ports throughout the world. The potato was slow to be adopted by 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.[7] 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 as well as parts of the Scottish Highlands, resulting in the crop failures that led to the Great Irish Famine.[30] Thousands of varieties still persist in the Andes however, where over 100 cultivars might be found in a single valley, and a dozen or more might be maintained by a single agricultural household.[57]

Production

Potato production – 2016
Country Production (millions of tonnes)
 China
99.1
 European Union
56.2
 India
43.8
 Russia
31.1
 Ukraine
21.8
 United States
20.0
World
376.8
Source: FAOSTAT of the United Nations[58]
Global production of potatoes in 2008

In 2016, world production of potatoes was 377 million tonnes, led by China with over 26% of the world total (see table). Other major producers were India, Russia, Ukraine and the United States. It remains an essential crop in Europe (especially northern and eastern 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.[8][58]

Nutrition

A raw potato is 79% water, 17% carbohydrates (88% is starch), 2% protein, and contains negligible fat (see table). In an amount measuring 100 grams (3.5 oz), raw potato provides 322 kilojoules (77 kilocalories) of energy and is a rich source of vitamin B6 and vitamin C (23% and 24% of the Daily Value, respectively), with no other vitamins or minerals in significant amount (see table). The potato is rarely eaten raw because raw potato starch is poorly digested by humans.[59] When a potato is baked, its contents of vitamin B6 and vitamin C decline notably, while there is little significant change in the amount of other nutrients.[60]

Potatoes are often broadly classified as having a high glycemic index (GI) and so are often excluded from the diets of individuals trying to follow a low-GI diet. The GI of potatoes can vary considerably depending on the cultivar or cultivar category (such as "red", russet, "white", or King Edward), growing conditions and storage, preparation methods (by cooking method, whether it is eaten hot or cold, whether it is mashed or cubed or consumed whole), and accompanying foods consumed (especially the addition of various high-fat or high-protein toppings).[61] In particular, consuming reheated or cooled potatoes that were previously cooked may yield a lower GI effect.[61]

In the UK, potatoes are not considered by the National Health Service (NHS) as counting or contributing towards the recommended daily five portions of fruit and vegetables, the 5-A-Day program.[62]

Comparison to other staple foods

This table shows the nutrient content of potatoes next to other major staple foods, each one measured in its respective raw state, even though staple foods are not commonly eaten raw and are usually sprouted or cooked before eating. In sprouted and cooked form, the relative nutritional and anti-nutritional contents of each of these grains (or other foods) may be different from the values in this table. Each nutrient (every row) has the highest number highlighted to show the staple food with the greatest amount in a 100-gram raw portion.

Nutrient content of 10 major staple foods per 100 g portion,[63] in order of rank
Nutrient Maize (corn)[A] Rice, white[B] Wheat[C] Potatoes[D] Cassava[E] Soybeans, green[F] Sweet potatoes[G] Yams[Y] Sorghum[H] Plantain[Z] RDA
Water (g) 10 12 13 79 60 68 77 70 9 65 3,000
Energy (kJ) 1,528 1,528 1,369 322 670 615 360 494 1,419 511 8,368–10,460
Protein (g) 9.4 7.1 12.6 2.0 1.4 13.0 1.6 1.5 11.3 1.3 50
Fat (g) 4.74 0.66 1.54 0.09 0.28 6.8 0.05 0.17 3.3 0.37 44–77
Carbohydrates (g) 74 80 71 17 38 11 20 28 75 32 130
Fiber (g) 7.3 1.3 12.2 2.2 1.8 4.2 3 4.1 6.3 2.3 30
Sugar (g) 0.64 0.12 0.41 0.78 1.7 0 4.18 0.5 0 15 minimal
Minerals [A] [B] [C] [D] [E] [F] [G] [Y] [H] [Z] RDA
Calcium (mg) 7 28 29 12 16 197 30 17 28 3 1,000
Iron (mg) 2.71 0.8 3.19 0.78 0.27 3.55 0.61 0.54 4.4 0.6 8
Magnesium (mg) 127 25 126 23 21 65 25 21 0 37 400
Phosphorus (mg) 210 115 288 57 27 194 47 55 287 34 700
Potassium (mg) 287 115 363 421 271 620 337 816 350 499 4,700
Sodium (mg) 35 5 2 6 14 15 55 9 6 4 1,500
Zinc (mg) 2.21 1.09 2.65 0.29 0.34 0.99 0.3 0.24 0 0.14 11
Copper (mg) 0.31 0.22 0.43 0.11 0.10 0.13 0.15 0.18 - 0.08 0.9
Manganese (mg) 0.49 1.09 3.99 0.15 0.38 0.55 0.26 0.40 - - 2.3
Selenium (μg) 15.5 15.1 70.7 0.3 0.7 1.5 0.6 0.7 0 1.5 55
Vitamins [A] [B] [C] [D] [E] [F] [G] [Y] [H] [Z] RDA
Vitamin C (mg) 0 0 0 19.7 20.6 29 2.4 17.1 0 18.4 90
Thiamin (B1) (mg) 0.39 0.07 0.30 0.08 0.09 0.44 0.08 0.11 0.24 0.05 1.2
Riboflavin (B2) (mg) 0.20 0.05 0.12 0.03 0.05 0.18 0.06 0.03 0.14 0.05 1.3
Niacin (B3) (mg) 3.63 1.6 5.46 1.05 0.85 1.65 0.56 0.55 2.93 0.69 16
Pantothenic acid (B5) (mg) 0.42 1.01 0.95 0.30 0.11 0.15 0.80 0.31 - 0.26 5
Vitamin B6 (mg) 0.62 0.16 0.3 0.30 0.09 0.07 0.21 0.29 - 0.30 1.3
Folate Total (B9) (μg) 19 8 38 16 27 165 11 23 0 22 400
Vitamin A (IU) 214 0 9 2 13 180 14,187 138 0 1,127 5,000
Vitamin E, alpha-tocopherol (mg) 0.49 0.11 1.01 0.01 0.19 0 0.26 0.39 0 0.14 15
Vitamin K1 (μg) 0.3 0.1 1.9 1.9 1.9 0 1.8 2.6 0 0.7 120
Beta-carotene (μg) 97 0 5 1 8 0 8,509 83 0 457 10,500
Lutein+zeaxanthin (μg) 1,355 0 220 8 0 0 0 0 0 30 6,000
Fats [A] [B] [C] [D] [E] [F] [G] [Y] [H] [Z] RDA
Saturated fatty acids (g) 0.67 0.18 0.26 0.03 0.07 0.79 0.02 0.04 0.46 0.14 minimal
Monounsaturated fatty acids (g) 1.25 0.21 0.2 0.00 0.08 1.28 0.00 0.01 0.99 0.03 22–55
Polyunsaturated fatty acids (g) 2.16 0.18 0.63 0.04 0.05 3.20 0.01 0.08 1.37 0.07 13–19
[A] [B] [C] [D] [E] [F] [G] [Y] [H] [Z] RDA

A raw yellow dent corn
B raw unenriched long-grain white rice
C raw hard red winter wheat
D raw potato with flesh and skin
E raw cassava
F raw green soybeans
G raw sweet potato
H raw sorghum
Y raw yam
Z raw plantains
/* unofficial

Toxicity

'Early Rose' variety seed tuber with sprouts
Potato fruit, which is not edible

Potatoes contain toxic compounds known as glycoalkaloids, of which the most prevalent are solanine and chaconine. Solanine is found in other plants in the same family, Solanaceae, which includes such plants as deadly nightshade (Atropa belladonna), henbane (Hyoscyamus niger) and tobacco (Nicotiana spp.), as well as the food plants eggplant and tomato. These compounds, which protect the potato plant from its predators, are generally concentrated in its leaves, flowers, sprouts, and fruits (in contrast to the tubers).[64] In a summary of several studies, the glycoalkaloid content was highest in the flowers and sprouts and lowest in the tuber flesh. (The glycoalkaloid content was, in order from highest to lowest: flowers, sprouts, leaves, skin[clarification needed], roots, berries, peel [skin plus outer cortex of tuber flesh], stems, and tuber flesh.)[11]

Exposure to light, physical damage, and age increase glycoalkaloid content within the tuber.[12] Cooking at high temperatures—over 170 °C (338 °F)—partly destroys these compounds. The concentration of glycoalkaloids in wild potatoes is sufficient to produce toxic effects in humans. Glycoalkaloid poisoning may cause headaches, diarrhea, cramps, and, in severe cases, coma and death. However, poisoning from cultivated potato varieties is very rare. Light exposure causes greening from chlorophyll synthesis, giving a visual clue as to which areas of the tuber may have become more toxic. However, this does not provide a definitive guide, as greening and glycoalkaloid accumulation can occur independently of each other.

Different potato varieties contain different levels of glycoalkaloids. The Lenape variety was released in 1967 but was withdrawn in 1970 as it contained high levels of glycoalkaloids.[65] Since then, breeders developing new varieties test for this, and sometimes have to discard an otherwise promising cultivar. Breeders try to keep glycoalkaloid levels below 200 mg/kg (200 ppmw). However, when these commercial varieties turn green, they can still approach solanine concentrations 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.[66] While a normal potato tuber has 12–20 mg/kg of glycoalkaloid content, a green potato tuber contains 250–280 mg/kg and its skin has 1500–2200 mg/kg.[67]

Growth and cultivation

Potato planting
Potato field in Fort Fairfield, Maine

Seed potatoes

Potatoes are generally grown from seed potatoes, tubers specifically grown to be free from disease and to provide consistent and healthy plants. To be disease free, the areas where seed potatoes are grown are selected with care. In the US, this restricts production of seed potatoes to only 15 states out of all 50 states where potatoes are grown.[68] These locations are selected for their cold, hard winters that kill pests and summers with long sunshine hours for optimum growth. In the UK, most seed potatoes originate in Scotland, in areas where westerly winds reduce aphid attack and the spread of potato virus pathogens.[69][failed verification]

Phases of growth

Potato growth can be divided into five phases. During the first phase, sprouts emerge from the seed potatoes and root growth begins. During the second, photosynthesis begins as the plant develops leaves and branches above-ground and stolons develop from lower leaf axils on the below-ground stem. In the third phase the tips of the stolons swell forming new tubers and the shoots continue to grow and flowers typically develop soon after. Tuber bulking occurs during the fourth phase, when the plant begins investing the majority of its resources in its newly formed tubers. At this phase, several factors are critical to a good yield: optimal soil moisture and temperature, soil nutrient availability and balance, and resistance to pest attacks. The fifth phase is the maturation of the tubers: the plant canopy dies back, the tuber skins harden, and the sugars in the tubers convert to starches.[70][71]

Preparation of a potato crop in Hesbaye, Belgium

Challenges

Potatoes grown in a tall bag are common in gardens as they minimize the amount of digging required at harvest

New tubers may start growing at the surface of the soil. Since exposure to light leads to an undesirable greening of the skins and the development of