Wheat
From Wikipedia, the free encyclopedia
Wheat
Scientific classification
Kingdom: Plantae
Division:
Magnoliophyta
Class:
Liliopsida
Order:
Poales
Family:
Poaceae
Subfamily: Pooideae
Tribe:
Triticeae
Genus:
Triticum
Species
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.)[1] is a grass that is cultivated worldwide. Globally, it is the most
important human food grain and ranks second in total production as a cereal crop behind
maize; the third being rice.[2] Wheat grain is a staple food used to make flour for
leavened, flat and steamed breads; cookies, cakes, pasta, noodles and couscous;[3] and for
fermentation to make beer,[4] alcohol, vodka[5] or biofuel[6]. The husk of the grain,
separated when milling white flour, is bran.[7] 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.[8][9]
Contents
•
1 History
•
2 Genetics and breeding
3 Hulled versus free-threshing wheat
•
•
•
•
•
4 Naming
o 4.1 Major cultivated species of
wheat
5 Economics
6 Production and consumption statistics
7 Agronomy
o
o
o
o
•
•
7.1 Crop development
7.2 Wheat stages
7.3 Diseases
7.4 Pests
8 Wheat in the United States
9 References
History
The first cereal known to have been domesticated, wheat originated in southwest Asia in
the area known as the Fertile Crescent. The earliest archaeological evidence for wheat
cultivation comes from the Levant and Turkey. Around 10,000 years ago,[10] wild einkorn
and emmer wheat were domesticated as part of the origins of agriculture in the fertile
crescent. Cultivation and repeated harvesting and sowing of the grains of wild grasses led
to the selection of mutant forms with tough ears which remained attached to the ear
during the harvest process, and larger grains. (Selection for these traits is an important
part of crop domestication). Because of the loss of seed dispersal mechanisms,
domesticated wheats cannot survive in the wild.[11]
The cultivation of wheat began to spread beyond the Fertile Crescent during the Neolithic
period. By 5,000 B.P., wheat had reached Ethiopia, India, Ireland and Spain. A
millennium later it reached China.[11] Agricultural cultivation using horse collar leveraged
plows (3000 years B.P.) increased cereal grain productivity yields, as did the use of seed
drills which replaced broadcasting sowing of seed in the 18th century. Yields of wheat
continued to increase, as new land came under cultivation and with improved agricultural
husbandry involving the use of fertilizers, threshing machines and reaping machines (the
'combine harvester'), tractor-draw cultivators and planters, and better varieties (see green
revolution and Norin 10 wheat). With population growth rates falling, while yields
continue to rise, the acreage devoted to wheat may now begin to decline for the first time
in modern human history.[12][9]
Genetics and breeding
Wheat genetics is more complicated than that of most other domesticated species. Some
wheat species occur as stable polyploids, having more than two sets of diploid
chromosomes.[13]
•
Einkorn wheat (T. monococcum) is diploid (2 chromosomes).[1]
•
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.[13]
•
Hexaploid wheats evolved in farmers' fields. Either emmer or durum wheat
hybridized with yet another wild diploid grass (Aegilops tauschii) to make the
hexaploid (6 chromosomes) wheats, spelt wheat and bread wheat.[13]
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 selfpollinate.[14] 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 commercially success, in Europe (particularly France), the USA and South
Africa.[15] F1 hybrid wheat cultivars should not be confused with standard method of
breeding inbred wheat cultivars by crossing two lines using hand emasculation, then
selfing or inbreeding the progeny many (ten or more) generations before release
selections are identified to released as a variety or cultivar.[14]
Hulled versus free-threshing wheat
Four wild species of wheat, and in the domesticated einkorn[16], emmer[17] and spelt[18]
wheats are hulled (in German, Spelzweizen). This more primitive morphology consists of
toughened glumes that tightly enclose the grains, and (in domesticated wheats) a semibrittle 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.[16]
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[9], 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 today.
•
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.
Spelt - (T. spelta) Another hexaploid species cultivated in limited quantities.
•
Kamut® or QK-77 - (T. polonicum or T. durum) A trademarked tetraploid
cultivar grown in small quantities that is extensively marketed. Originally from
the Middle East.
Economics
Sack of wheat
Cracked wheat
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, including many breads named for the other grains they contain like
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)
In 1997, global per capita wheat
China
96
India
72
United States
57
Russia
46
France
37
Canada
26
Australia
24
Germany
24
Pakistan
22
Turkey
21
World Total
626
Source:
UN Food & Agriculture Organisation (FAO)
consumption was 101 kg, with the
highest per capita consumption (623 kg)
found in Denmark.
Agronomy
Crop development
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 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)
•
Wheat a few days old
•
Wheat in spring
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 species including The
Flame, Rustic Shoulder-knot, Setaceous Hebrew Character and Turnip Moth.
Wheat in the United States
Wheat harvest on the
Palouse.
Combining wheat in
Hemingway, South Carolina.
Combining wheat in
Washington.
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 Exchange.
•
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 trade by the Kansas City
Board of Trade.
•
Soft Red Winter — Soft, low protein wheat used for cakes, pie crusts, biscuits,
and muffins. Cake Flour, for example, is made from soft red winter wheat. It is
•
primarily traded by the Chicago Board of Trade
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.
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 thinchaffed 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.
References
^ a b Belderok, Bob & Hans Mesdag & Dingena A. Donner. (2000) Bread-Making Quality of Wheat. Springer. p.3. ISBN 0-79236383-3.
^ FAOSTAT database of World Agriculture, 2006
^ Cauvain, Stanley P. & Cauvain P. Cauvain. (2003) Bread Making. CRC Press. p. 540. ISBN 1-85573-553-9.
^ Palmer, John J. (2001) How to Brew. Defenestrative Pub Co. p. 233. ISBN 0-9710579-0-7.
^ Neill, Richard. (2002) Booze: The Drinks Bible for the 21st Century. Octopus Publishing Group - Cassell Illustrated. p. 112. ISBN
1-841-88196-1.
^ Department of Agriculture Appropriations for 1957: Hearings ... 84th Congress. 2d Session. United States. Congress. House.
Appropriations. 1956. p. 242.
^ Ojakangas, Beatrice A. (2002) Great Whole Grain Breads. University of Minnesota Press. p. 48. ISBN 0-8166-4150-1.
^ Smith, Albert E. (1995) Handbook of Weed Management Systems. Marcel Dekker. p. 411. ISBN 0-8247-9547-4.
^ a b c Bridgwater, W. & Beatrice Aldrich. (1966) The Columbia-Viking Desk Encyclopedia. Columbia University. p. 1959.
^ Kingfisher Books. (2004) The Kingfisher History Encyclopedia. Kingfisher Publications. p. 8. ISBN 0-7534-5784-9.
^ a b Smith, C. Wayne. (1995) Crop Production. John Wiley and Sons. pp. 60-62. ISBN 0-471-07972-3.
^ The Economist, 2005
^ a b c Hancock, James F. (2004) Plant Evolution and the Origin of Crop Species. CABI Publishing. ISBN 0-85199-685-X.
^ a b Bajaj, Y. P. S. (1990) Wheat. Springer. pp. 161-63. ISBN 3-540-51809-6.
^ Basra, Amarjit S. (1999) Heterosis and Hybrid Seed Production in Agronomic Crops. Haworth Press. pp. 81-82. ISBN 1-56022-8768.
^ a b Potts, D. T. (1996) Mesopotamia Civilization: The Material Foundations Cornell University Press. p. 62. ISBN 0-8014-3339-8.
^ 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.
^ Vaughan, J. G. & P. A. Judd. (2003) The Oxford Book of Health Foods. Oxford University Press. p. 35. ISBN 0-19-850459-4.
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 24th 2005, pp. 28-30