Wheat (Triticum spp.)is a worldwide cultivated grass from the Levant area of the Middle East. Globally, after maize, wheat is the second most produced food among the cereal crops; rice ranks third.Wheat grain is a staple food used to make flour for leavened, flat and steamed breads; cookies, cakes, pasta, noodles and couscous;and for fermentation to make beer,alcohol, vodkaor 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 persons in the United States has Coeliac disease, a condition which results from an inappropriate immune system response to a protein found in wheat: gluten.
Wheat originated in Southwest Asia in the area known as the Fertile crescent. The genetic relationships between einkorn and emmer indicate that the most likely site of domestication is near Diyarbakır in Turkey. These wild wheats 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 domestication of wheat through selection of mutant forms with tough ears which remained intact during harvesting, larger grains, and a tendency for the spikelets to stay on the stalk until harvested. Because of the loss of seed dispersal mechanisms, domesticated wheats have limited capacity to propagate in the wild.
The cultivation of wheat began to spread beyond the Fertile Crescent during the Neolithic period. The oldest wheat found thus far is from Çatalhöyük, a Neolithic settlement in southern Anatolia. The wheat samples discovered were found to be 8,500 years old. By 5,000 years ago, wheat had reached Ethiopia, India, Great Britain, Ireland and Spain. A millennium later it reached China.Three thousand years ago agricultural cultivation with horse drawn plows increased cereal grain production, as did the use of seed drills to replace broadcast sowing 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, tractor-drawn cultivators and planters, and better varieties (see green revolution and Norin 10 wheat). With population growth rates falling in the more technologically advanced countries, while yields continue to rise, the area devoted to wheat may now begin to decline for the first time in modern human history.But now in 2007 wheat stocks have reached their lowest since 1981, and 2006 was the first year in which the world consumed more wheat than the world produced – a gap that is continuously widening as the requirement for wheat increases beyond production.
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, mositure and heat tolerance. The major diseases in temperate environments include Fusarium head blight, leaf rust and stem rust, whereas in tropical areas spot blotch (wheat) (also known as Helminthosporium leaf blight).
Raw wheat berries can be powdered into flour, germinated and dried creating malt, crushed and de-branned into cracked wheat, parboiled (or steamed), dried, crushed and de-branned into bulgur, or processed into semolina, pasta, or roux. They are a major ingredient in such foods as bread, breakfast cereals (e.g. Wheatena, Cream of Wheat, Shredded Wheat), porridge, crackers, biscuits, pancakes, cakes, gravy and boza (a fermented beverage).