Wheat
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{{Taxobox
| color = lightgreen
| name = Wheat
| image = Koeh-274.jpg
| image_width = 250px
| regnum = Plantae
| divisio = Magnoliophyta
| classis = Liliopsida
| ordo = Poales
| familia = Poaceae
| genus = Triticum
| genus_authority = L.
| subdivision_ranks = Species
| subdivision =
T. aestivum
T. aethiopicum
T. araraticum
T. boeoticum
T. carthlicum
T. compactum
T. dicoccoides
T. dicoccon
T. durum
T. ispahanicum
T. karamyschevii
T. macha
T. militinae
T. monococcum
T. polonicum
T. spelta
T. sphaerococcum
T. timopheevii
T. turanicum
T. turgidum
T. urartu
T. vavilovii
T. zhukovskyi
References:
ITIS 42236 2002-09-22
}}
Wheat (Triticum spp.) is a grass that is cultivated worldwide. Globally, it is the second-largest cereal crop behind maize; the third being rice<ref>FAOSTAT database of World Agriculture, 2006</ref>. Wheat grain is a staple food used to make flour, livestock feed and for fermentation to make alcohol (sometimes as an ingredient in the brewing of beer, or for distillation as vodka or fuel). The husk can be separated and ground into bran. Wheat is also planted as a forage crop for livestock and the straw can be used as a ruminant feed component or construction material (in fibre-boards, or thatch roofing material).
Contents |
History
Domestic wheat originated in the Middle East and southwest Asia in what is now known as the Fertile Crescent. The earliest archaeological evidence for wheat cultivation comes from Syria, Israel, Jordan, Turkey, and Iraq. Around 10,000 years ago, wild einkorn and emmer wheat were domesticated as part of the origins of agriculture in the fertile crescent. Cultivation of wild forms led to selection of mutations for tough-rachised ears (which do not break up at maturity) and larger grains (see domestication). While these forms could not have succeeded in the wild, under cultivation they produced more food for humans. Image:WheatPennsylvania1943.jpg
The cultivation of wheat began to spread into Europe beginning in the Neolithic period. 5,000 years ago wheat had reached Ireland, Spain, Ethiopia and India. A millennium later it reached China. Millennia later, the horse collar increased the yields, as did the seed drill (replacing broadcasting of seed) in the 18th century. Yields of wheat continued to increase, with more land under cultivation and new inventions like the tractor, threshing machines and then combined reaping, threshing and winnowing machines (the combined or 'combine harvester') and better fertilizers, and the green revolution varieties like Norin 10 wheat. Only recently, with population growth rates falling sharply while yields still continue to rise the acreage devoted to wheat may now begin to decline for the first time in human history<ref>The Economist, 2005</ref>.
Genetics and breeding
Wheat genetics is more complicated than that of most other domesticated species. Wheat is capable of forming stable polyploidy, or having more than two sets of chromosomes (diploid). For example, common bread wheat (T. aestivum) is hexaploid. A further complicating factor is that four out of five of the most common wheat species are the results of hybridization.
- Einkorn wheat (T. monococcum) is diploid (2x chromosomes).
- Tetraploid wheats (e.g. emmer and durum wheat) derive from wild emmer, T. dicoccoides. Wild emmer is the result of a hybridisation 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 emmer or durum wheat hybridized with yet another wild diploid grass (Aegilops tauschii) to make the hexaploid (6x chromosomes) wheats, spelt wheat and bread wheat.
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. Therefore commercial hybrid wheat seed is produced using chemical hybridizing agents, plant growth regulators that selectively interfere with pollen development. Hybrid wheat has been grown commercially in Europe (particularly France) since the 1990s. Hybrid wheats (F1) should not be confused with standard wheats bred by making hybrids using hand emasculation and crossing, then inbred for many (ten or more) generations before release as a variety.
Hulled versus free-threshing wheat
Image:Usdaeinkorn1.jpg All four wild species of wheat, and in the domesticated einkorn, emmer and spelt wheats are hulled (in German, Spelzweizen). This more primitive morphology 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
There are many taxonomic classification systems used for wheat species, discussed in a separate article on Wheat taxonomy. It is good to keep in mind that 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 growing season, such as winter wheat vs. spring wheat, and by gluten content, such as hard wheat (high gluten content) or soft wheat (high starch content).
Major cultivated species of wheat
- Common Wheat or Bread wheat - (T. aestivum) A hexaploid species that is the most widely cultivated in the world.
- Einkorn - (T. monococcum) A diploid species with wild and cultivated variants. One of the earliest cultivated but rarely planted today.
- Emmer - (T. dicoccon) A tetraploid species, cultivated in ancient times but no longer in widespread use.
- Durum - (T. durum) The only tetraploid form of wheat widely used today.
- Kamut® or QK-77 - (T. polonicum or T. durum) A trademarked tetraploid species grown in small quantities that is extensively marketed. Originally from the Middle East
- Spelt - (T. spelta) Another hexaploid species cultivated in limited quantities.
Economics
Image:Wheat in sack.jpg Harvested wheat grain is classified according to grain properties (see below) 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, even many breads named for the other grains they contain, including most rye and oat breads. Many other popular foods are made from wheat flour as well, resulting in a large demand for the grain even in economies with a significant food surplus.
Production and consumption statistics
| Top Ten Wheat Producers - 2005 (million metric ton) | |
|---|---|
| Template:CHN | 96 |
| Template:IND | 72 |
| Template:USA | 57 |
| Template:RUS | 46 |
| Template:FRA | 37 |
| Template:CAN | 26 |
| Template:AUS | 24 |
| Template:GER | 24 |
| Template:PAK | 22 |
| Template:TUR | 21 |
| World Total | 626 |
| Source: UN Food & Agriculture Organisation (FAO)[1] | |
1997 global per capita wheat consumption was 101 kg, led by Denmark at 623 kg.
See also International wheat production statistics.
Agronomy
Crop development
Image:Spiklet.JPG Crop management decisions require the knowledge of stage of development of the crop. In particular, spring fertilizers applications, herbicides, fungicides, growth regulators are typically applied at specific stages of plant development.
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 meïosis 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.
Wheat stages
- Wheat at the anthesis stage (face and side view)
| Image:WheatFlower1.jpg | Image:WheatFlower3.JPG |
- Wheat a few days old
| Image:Wheat harvest.jpg | Image:CombineWheat0654.JPG | Image:Harvestingwheatwashigton.JPG |
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.
- Hard Red Winter - Hard, brownish, very high protein wheat used for bread, hard baked goods and as an adjunct in other flours to increase protein.
- Soft Red Winter - Soft, brownish, medium protein wheat used for bread.
- 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 bread.
Hard wheats are harder to process and red wheats may need bleaching. Therefore, soft and white wheats usually command higher prices than hard and red wheats on the commodities market.
Much of the following text is taken from the Household Cyclopedia of 1881:
Wheat may be classed under two principal divisions, though each of these admits of several subdivisions. The first is composed of all the varieties of red wheat. The second division comprehends the whole varieties of white wheat, which again may be arranged under two distinct heads, namely, thick-chaffed and thin-chaffed.
Thick-chaffed wheat varieties were the most widely used before 1799, as they generally make the best quality flour, and in dry seasons, equal the yields of thin-chaffed varieties. However, thick-chaffed varieties are particularly susceptible to mildew, while thin-chaffed varieties are quite hardy and in general are more resistant to mildew. Consequently, a widespread outbreak of mildew in 1799 began a gradual decline in the popularity of thick-chaffed varieties.
See also
- Norin 10 wheat
- Granular material
- Buckwheat - despite its name, it is not wheat
References
- Bonjean, A.P., and W.J. Angus (editors). The World Wheat Book: a history of wheat breeding. Lavoisier Publ., Paris. 1131 pp. (2001). ISBN 2-7430-0402-9.
- Ears of plenty: The story of wheat, The Economist, Dec 20th 2005
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External links
- NAWG – Web site of the National Association of Wheat Growers
- CIMMYT – Web site of the International Maize and Wheat Improvement Center
- Triticum species at Purdue University
- A Workshop Report on Wheat Genome Sequencing
- Proceedings of the First International Workshop on Hulled Wheats (PDF) July 1995
- Molecular Genetic Maps in Wild Emmer WheatTemplate:Link FA
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Categories: Cereals | Grains | Grasses | Wheat