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Wheat (Triticum spp.) is a worldwide cultivated grass from the Fertile Crescent region of the Near East. In 2007 world production of wheat was 607 million tons, making it the third most-produced cereal after maize (784 million tons) and rice (651 million tons). Wheat grain is a staple food used to make flour for leavened, flat and steamed breads, biscuits, cookies, cakes, breakfast cereal, pasta, noodles, couscous and for fermentation to make beer, alcohol, vodka, or biofuel. Wheat is planted to a limited extent as a forage crop for livestock, and the straw can be used as fodder for livestock or as a construction material for roofing thatch.

Although wheat supplies much of the world's dietary protein and food supply, as many as one in every 100 to 200 people has Celiac disease, a condition which results from an immune system response to a protein found in wheat: gluten (based on figures for the United Statesmarker).

History

Wheat has been cultivated domestically at least since 9,000 B.C. and probably earlier. Domesticated Einkorn wheat at Nevali Cori 40 miles northwest of Gobekli Tepemarker in Turkeymarker has been dated to 9,000 B.C.

However evidence for the exploitation of wild barley has been dated to 23,000 B.C. and some say this is also true of pre-domesticated wheat.

Genetics

Wheat genetics is more complicated than that of most other domesticated species. Some wheat species are diploid, with two sets of chromosomes, but many are stable polyploids, with four sets of chromosomes (tetraploid) or six (hexaploid).
  • Einkorn wheat (T. monococcum) is diploid.
  • Most tetraploid wheats (e.g. emmer and durum wheat) are derived from wild emmer, T. dicoccoides. Wild emmer is the result of a hybridization between two diploid wild grasses, T. urartu and a wild goatgrass such as Aegilops searsii or Ae. speltoides. The hybridization that formed wild emmer occurred in the wild, long before domestication.
  • Hexaploid wheats evolved in farmers' fields. Either domesticated emmer or durum wheat hybridized with yet another wild diploid grass (Aegilops tauschii) to make the hexaploid wheats, spelt wheat and bread wheat.


Plant breeding

Wheat
Wheat
Wheat
In traditional agricultural systems wheat populations often consist of landraces, informal farmer-maintained populations that often maintain high levels of morphological diversity. Although landraces of wheat are no longer grown in Europe and North America, they continue to be important elsewhere. The origins of formal wheat breeding lie in the nineteenth century, when single line varieties were created through selection of seed from a single plant noted to have desired properties. Modern wheat breeding developed in the first years of the twentieth century and was closely linked to the development of Mendelian genetics. The standard method of breeding inbred wheat cultivars is by crossing two lines using hand emasculation, then selfing or inbreeding the progeny. Selections are identified (shown to have the genes responsible for the varietal differences) ten or more generations before release as a variety or cultivar.

F1 hybrid wheat cultivars should not be confused with wheat cultivars deriving from standard plant breeding. Heterosis or hybrid vigor (as in the familiar F1 hybrids of maize) occurs in common (hexaploid) wheat, but it is difficult to produce seed of hybrid cultivars on a commercial scale as is done with maize because wheat flowers are complete and normally self-pollinate. Commercial hybrid wheat seed has been produced using chemical hybridizing agents, plant growth regulators that selectively interfere with pollen development, or naturally occurring cytoplasmic male sterility systems. Hybrid wheat has been a limited commercial success in Europe (particularly Francemarker), the USA and South Africa.

The major breeding objectives include high grain yield, good quality, disease and insect resistance and tolerance to abiotic stresses include mineral, moisture and heat tolerance. The major diseases in temperate environments include Fusarium head blight, leaf rust and stem rust, whereas in tropical areas spot blotch (also known as Helminthosporium leaf blight).

Hulled versus free-threshing wheat

A mature wheat field
The four wild species of wheat, along with the domesticated varieties einkorn, emmer and spelt, have hulls. This more primitive morphology (in evolutionary terms) consists of toughened glumes that tightly enclose the grains, and (in domesticated wheats) a semi-brittle rachis that breaks easily on threshing. The result is that when threshed, the wheat ear breaks up into spikelets. To obtain the grain, further processing, such as milling or pounding, is needed to remove the hulls or husks. In contrast, in free-threshing (or naked) forms such as durum wheat and common wheat, the glumes are fragile and the rachis tough. On threshing, the chaff breaks up, releasing the grains. Hulled wheats are often stored as spikelets because the toughened glumes give good protection against pests of stored grain.

Naming

Sack of wheat
There are many botanical classification systems used for wheat species, discussed in a separate article on Wheat taxonomy. The name of a wheat species from one information source may not be the name of a wheat species in another. Within a species, wheat cultivars are further classified by wheat breeders and farmers in terms of growing season, such as winter wheat vs. spring wheat, by gluten content, such as hard wheat (high protein content) vs. soft wheat (high starch content), or by grain color (red, white or amber).

Major cultivated species of wheat

  • Common wheat or Bread wheat — (T. aestivum) A hexaploid species that is the most widely cultivated in the world.
  • Durum — (T. durum) The only tetraploid form of wheat widely used today, and the second most widely cultivated wheat.
  • Einkorn — (T. monococcum) A diploid species with wild and cultivated variants. Domesticated at the same time as emmer wheat, but never reached the same importance.
  • Emmer — (T. dicoccum) A tetraploid species, cultivated in ancient times but no longer in widespread use.
  • Spelt — (T. spelta) Another hexaploid species cultivated in limited quantities.


Classes used in the United States are

  • Durum — Very hard, translucent, light colored grain used to make semolina flour for pasta.
  • Hard Red Spring — Hard, brownish, high protein wheat used for bread and hard baked goods. Bread Flour and high gluten flours are commonly made from hard red spring wheat. It is primarily traded at the Minneapolis Grain Exchangemarker.
  • Hard Red Winter — Hard, brownish, mellow high protein wheat used for bread, hard baked goods and as an adjunct in other flours to increase protein in pastry flour for pie crusts. Some brands of unbleached all-purpose flours are commonly made from hard red winter wheat alone. It is primarily traded by the Kansas City Board of Trade. One variety is known as "turkey red wheat", and was brought to Kansas by Mennonite immigrants from Russia.
  • Soft Red Winter — Soft, low protein wheat used for cakes, pie crusts, biscuits, and muffins. Cake flour, pastry flour, and some self-rising flours with baking powder and salt added for example, are made from soft red winter wheat. It is primarily traded by the Chicago Board of Trademarker.
  • Hard White — Hard, light colored, opaque, chalky, medium protein wheat planted in dry, temperate areas. Used for bread and brewing.
  • Soft White — Soft, light colored, very low protein wheat grown in temperate moist areas. Used for pie crusts and pastry. Pastry flour, for example, is sometimes made from soft white winter wheat.


Red wheats may need bleaching, therefore white wheats usually command higher prices than red wheats on the commodities market.

As a food

Cracked wheat


Raw wheat can be powdered into flour; germinated and dried creating malt; crushed or cut into cracked wheat; parboiled (or steamed), dried, crushed and de-branned into bulgur; or processed into semolina, pasta, or roux. Wheat is a major ingredient in such foods as bread, porridge, crackers, biscuits, Muesli, pancakes, pies, pastries, cakes, cookies, muffins, rolls, doughnuts, gravy, boza (a fermented beverage), and breakfast cereals (e.g. Wheatena, Cream of Wheat, Shredded Wheat, and Wheaties).

Nutrition

100 grams of hard red winter wheat contain about 12.6 grams of protein, 1.5 grams of total fat, 71 grams of carbohydrate (by difference), 12.2 grams of dietary fiber, and 3.2 mg of iron (17% of the daily requirement); the same weight of hard red spring wheat contains about 15.4 grams of protein, 1.9 grams of total fat, 68 grams of carbohydrate (by difference), 12.2 grams of dietary fiber, and 3.6 mg of iron (20% of the daily requirement). USDA National Nutrient Database for Standard Reference, Release 19 (2006)

Gluten, a protein found in wheat (and other Triticeae), cannot be tolerated by people with celiac disease (an autoimmune disorder in ~1% of Indo-European populations).

Much of the carbohydrate fraction of wheat is starch. Wheat starch is an important commercial product of wheat, but second in economic value to wheat gluten. The principal parts of wheat flour are gluten and starch. These can be separated in a kind of home experiment, by mixing flour and water to form a small ball of dough, and kneading it gently while rinsing it in a bowl of water. The starch falls out of the dough and sinks to the bottom of the bowl, leaving behind a ball of gluten.

Health concerns

Roughly 1% of the population has coeliac (also written as celiac) disease—a condition that is caused by an adverse immune system reaction to gliadin, a gluten protein found in wheat (and similar proteins of the tribe Triticeae which includes other species such as barley and rye). Upon exposure to gliadin, the enzyme tissue transglutaminase modifies the protein, and the immune system cross-reacts with the bowel tissue, causing an inflammatory reaction. That leads to flattening of the lining of the small intestine, which interferes with the absorption of nutrients. The only effective treatment is a lifelong gluten-free diet. While the disease is caused by a reaction to wheat proteins, it is not the same as wheat allergy.

Commercial use

Wheat output in 2005
Harvested wheat grain that enters trade is classified according to grain properties for the purposes of the commodities market. Wheat buyers use the classifications to help determine which wheat to purchase as each class has special uses. Wheat producers determine which classes of wheat are the most profitable to cultivate with this system.

Wheat is widely cultivated as a cash crop because it produces a good yield per unit area, grows well in a temperate climate even with a moderately short growing season, and yields a versatile, high-quality flour that is widely used in baking. Most breads are made with wheat flour, including many breads named for the other grains they contain like most rye and oat breads. The popularity of foods made from wheat flour creates a large demand for the grain, even in economies with significant food surpluses.
Utensil made of dry wheat branches for loaves of bread
In 2007 there was a dramatic rise in the price of wheat due to freezes and flooding in the northern hemisphere and a drought in Australia. Wheat futures in September, 2007 for December and March delivery had risen above $9.00 a bushel, prices never seen before. There were complaints in Italy about the high price of pasta. This followed a wider trend of escalating food prices around the globe, driven in part by climatic conditions such as drought in Australia, the diversion of arable land to other uses (such as producing government-subsidised bio-oil crops), and later by some food-producing nations placing bans or restrictions on exports in order to satisfy their own consumers.

Other drivers affecting wheat prices include the movement to bio fuels (in 2008, a third of corn crops in the US are expected to be devoted to ethanol production) and rising incomes in developing countries, which is causing a shift in eating patterns from predominantly rice to more meat based diets (a rise in meat production equals a rise in grain consumption - seven kilograms of grain is required to produce one kilogram of beef.

Production and consumption statistics

In 2003, global per capita wheat consumption was 67 kg, with the highest per capita consumption (239 kg) found in Kyrgyzstanmarker.

Unlike rice, wheat production is more widespread globally though China's share is almost one-sixth of the world.

Top Ten Wheat Producers — 2007 (million metric ton)
124.7
104
69.3
49.3
44.9
25.2
21.7
17.5
15.2
14.8
World Total 725
Source: UN Food & Agriculture Organisation (FAO)


Agronomy

Wheat spikelet with the three anthers sticking out
While winter wheat lies dormant during a winter freeze, wheat normally requires between 110 and 130 days between planting and harvest, depending upon climate, seed type, and soil conditions.Crop management decisions require the knowledge of stage of development of the crop. In particular, spring fertilizer applications, herbicides, fungicides, growth regulators are typically applied at specific stages of plant development.
Wheat ear
For example, current recommendations often indicate the second application of nitrogen be done when the ear (not visible at this stage) is about 1 cm in size (Z31 on Zadoks scale). Knowledge of stages is also interesting to identify periods of higher risk, in terms of climate. For example, the meiosis stage is extremely susceptible to low temperatures (under 4 °C) or high temperatures (over 25 °C). Farmers also benefit from knowing when the flag leaf (last leaf) appears as this leaf represents about 75% of photosynthesis reactions during the grain-filling period and as such should be preserved from disease or insect attacks to ensure a good yield.

Several systems exist to identify crop stages, with the Feekes and Zadoks scales being the most widely used. Each scale is a standard system which describes successive stages reached by the crop during the agricultural season.

Face view
Side view


Diseases

Estimates of the amount of wheat production lost owing to plant diseases vary between 10-25% in Missouri. A wide range of organisms infect wheat, of which the most important are viruses and fungi.

Pests

Wheat is used as a food plant by the larvae of some Lepidoptera (butterfly and moth) species including The Flame, Rustic Shoulder-knot, Setaceous Hebrew Character and Turnip Moth.

Futures contracts

Wheat futures are traded on the Chicago Board of Trademarker, Kansas City Board of Trade, and Minneapolis Grain Exchangemarker, and have delivery dates in March (H), May (K), July (N), September (U), and December (Z).

See also



References

  1. Belderok, Bob & Hans Mesdag & Dingena A. Donner. (2000) Bread-Making Quality of Wheat. Springer. p.3. ISBN 0-7923-6383-3.
  2. Cauvain, Stanley P. & Cauvain P. Cauvain. (2003) Bread Making. CRC Press. p. 540. ISBN 1-85573-553-9.
  3. Palmer, John J. (2001) How to Brew. Defenestrative Pub Co. p. 233. ISBN 0-9710579-0-7.
  4. Neill, Richard. (2002) Booze: The Drinks Bible for the 21st Century. Octopus Publishing Group - Cassell Illustrated. p. 112. ISBN 1-84188-196-1.
  5. Department of Agriculture Appropriations for 1957: Hearings ... 84th Congress. 2d Session. United States. Congress. House. Appropriations. 1956. p. 242.
  6. Smith, Albert E. (1995) Handbook of Weed Management Systems. Marcel Dekker. p. 411. ISBN 0-8247-9547-4.
  7. Bridgwater, W. & Beatrice Aldrich. (1966) The Columbia-Viking Desk Encyclopedia. Columbia University. p. 1959.
  8. Hill, I. D., Horvath, K., and Fasano, A., Epidemiology of celiac disease. 1: Am J Gastroenterol. 1995 Jan;90(1):163-4
  9. Hancock, James F. (2004) Plant Evolution and the Origin of Crop Species. CABI Publishing. ISBN 0-85199-685-X.
  10. Bajaj, Y. P. S. (1990) Wheat. Springer. pp. 161-63. ISBN 3-540-51809-6.
  11. Basra, Amarjit S. (1999) Heterosis and Hybrid Seed Production in Agronomic Crops. Haworth Press. pp. 81-82. ISBN 1-56022-876-8.
  12. Potts, D. T. (1996) Mesopotamia Civilization: The Material Foundations Cornell University Press. p. 62. ISBN 0-8014-3339-8.
  13. Nevo, Eviatar & A. B. Korol & A. Beiles & T. Fahima. (2002) Evolution of Wild Emmer and Wheat Improvement: Population Genetics, Genetic Resources, and Genome.... Springer. p. 8. ISBN 3-540-41750-8.
  14. Vaughan, J. G. & P. A. Judd. (2003) The Oxford Book of Health Foods. Oxford University Press. p. 35. ISBN 0-19-850459-4.
  15. Moon, David, "In the Russian Steppes: the Introduction of Russian Wheat on the Great Plains of the UNited States," Journal of Global History 3 (2008), 203-225
  16. International Starch Institute, TM 33-1www - ISI Technical Memorandum on Production of Wheat Starch. Retrieved August 11, 2008.
  17. "Wheat futures again hit new highs" article by Victoria Sizemore Long in The Kansas City Star September 28, 2007
  18. "Wheat Prices Send Italian Pasta Costs Up" Associated Press story by Colleen Barry, September 13, 2007 By COLLEEN BARRY – Sep 13, 2007
  19. "Broker picks in the soft commodities sector" in CompareShares April 2, 2008
  20. http://faostat.fao.org/ FAOSTAT
  21. List of Commodity Delivery Dates on Wikinvest


Further reading

  • Bonjean, A.P., and W.J. Angus (editors). The World Wheat Book: a history of wheat breeding. Lavoisier Publ., Paris. 1131 pp. (2001). ISBN 2743004029
  • Garnsey Peter, Grain for Rome, in Garnsey P., Hopkins K., Whittaker C. R. (editors), Trade in the Ancient Economy, Chatto & Windus, London 1983
  • Jasny Naum, The daily bread of ancient Greeks and Romans, Ex Officina Templi, Brugis 1950
  • Jasny Naum, The Wheats of Classical Antiquity, J. Hopkins Press, Baltimore 1944
  • Heiser Charles B., Seed to civilisation. The story of food, Harvard University Press, Harvard Mass. 1990
  • Harlan Jack R., Crops and man, American Society of Agronomy, Madison 1975
  • Saltini Antonio, I semi della civiltà. Grano, riso e mais nella storia delle società umane, Prefazione di Luigi Bernabò Brea, Avenue Media, Bologna 1996
  • Sauer Jonathan D., Geography of Crop Plants. A Select Roster, CRC Press, Boca Raton


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