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 States
).
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 Tepe
in Turkey
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 France
), 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 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 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
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.
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 Kyrgyzstan
.
Unlike rice, wheat production is more widespread globally though
China's share is almost one-sixth of the world.
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
Trade, Kansas City
Board of Trade, and Minneapolis Grain Exchange, and have delivery dates in March (H), May (K),
July (N), September (U), and December (Z).
See also
References
- Belderok, Bob & Hans Mesdag & Dingena A. Donner. (2000)
Bread-Making Quality of Wheat. Springer. p.3. ISBN
0-7923-6383-3.
- 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 1-84188-196-1.
- Department of Agriculture Appropriations for 1957: Hearings
... 84th Congress. 2d Session. United States. Congress.
House. Appropriations. 1956. p. 242.
- Smith, Albert E. (1995) Handbook of Weed Management
Systems. Marcel Dekker. p. 411. ISBN 0-8247-9547-4.
- Bridgwater, W. & Beatrice Aldrich. (1966) The
Columbia-Viking Desk Encyclopedia. Columbia University. p.
1959.
- Hill, I. D., Horvath, K., and Fasano, A., Epidemiology of
celiac disease. 1: Am J Gastroenterol. 1995
Jan;90(1):163-4
- Hancock, James F. (2004) Plant Evolution and the Origin of
Crop Species. CABI Publishing. ISBN 0-85199-685-X.
- 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
1-56022-876-8.
- 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.
- 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
- International Starch Institute, TM 33-1www - ISI Technical Memorandum on Production of
Wheat Starch. Retrieved August 11, 2008.
- "Wheat futures again hit new highs" article by
Victoria Sizemore Long in The Kansas City Star
September 28, 2007
- "Wheat Prices Send Italian Pasta Costs Up"
Associated
Press story by Colleen Barry, September 13, 2007 By COLLEEN
BARRY – Sep 13, 2007
- "Broker picks in the soft commodities sector" in
CompareShares April 2, 2008
- http://faostat.fao.org/ FAOSTAT
- 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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