Wheat is a grass widely cultivated for its seed, a cereal grain that is a worldwide staple food. The many species of wheat together make up the genus Triticum /ˈtrɪtɪkəm/; the most widely grown is common wheat (T. aestivum). The archaeological record suggests that wheat was first cultivated in the regions of the Fertile Crescent around 9600 BCE. Botanically, the wheat kernel is a type of fruit called a caryopsis.
In 2020, world production of wheat was 761 million tonnes (839 million short tons; 1.7 trillion pounds), making it the second most-produced cereal after maize. Since 1960, world production of wheat and other grain crops has tripled and is expected to grow further through the middle of the 21st century. Global demand for wheat is increasing due to the unique viscoelastic and adhesive properties of gluten proteins, which facilitate the production of processed foods, whose consumption is increasing as a result of the worldwide industrialization process and the westernization of the diet.
Wheat is an important source of carbohydrates. Globally, it is the leading source of vegetable proteins in human food, having a protein content of about 13%, which is relatively high compared to other major cereals but relatively low in protein quality for supplying essential amino acids. When eaten as the whole grain, wheat is a source of multiple nutrients and dietary fiber.
Cultivation and repeated harvesting and sowing of the grains of wild grasses led to the creation of domestic strains, as mutant forms ('sports') of wheat were preferentially chosen by farmers. In domesticated wheat, grains are larger, and the seeds (inside the spikelets) remain attached to the ear by a toughened rachis during harvesting. In wild strains, a more fragile rachis allows the ear to easily shatter and disperse the spikelets. Selection for larger grains and non-shattering heads by farmers might not have been deliberately intended, but simply have occurred because these traits made gathering the seeds easier; nevertheless such 'incidental' selection was an important part of crop domestication. As the traits that improve wheat as a food source also involve the loss of the plant's natural seed dispersal mechanisms, highly domesticated strains of wheat cannot survive in the wild.
Archaeological analysis of wild emmer indicates that it was first cultivated in the southern Levant, with finds dating back as far as 9600 BC. Genetic analysis of wild einkorn wheat suggests that it was first grown in the Karacadaǧ Mountains in southeastern Turkey. Dated archaeological remains of einkorn wheat in settlement sites near this region, including those at Abu Hureyra in Syria, suggest the domestication of einkorn near the Karacadaǧ Mountains. With the anomalous exception of two grains from Iraq ed-Dubb, the earliest carbon-14 date for einkorn wheat remains at Abu Hureyra is 7800 to 7500 years BC.
Remains of harvested emmer from several sites near the Karacadag Range have been dated to between 8600 (at Cayonu) and 8400 BC (Abu Hureyra), that is, in the Neolithic period. With the exception of Iraq ed-Dubb, the earliest carbon-14 dated remains of domesticated emmer wheat were found in the earliest levels of Tell Aswad, in the Damascus basin, near Mount Hermon in Syria. These remains were dated by Willem van Zeist and his assistant Johanna Bakker-Heeres to 8800 BC. They also concluded that the settlers of Tell Aswad did not develop this form of emmer themselves, but brought the domesticated grains with them from an as yet unidentified location elsewhere.
The cultivation of emmer reached Greece, Cyprus and Indian subcontinent by 6500 BC, Egypt shortly after 6000 BC, and Germany and Spain by 5000 BC. \"The early Egyptians were developers of bread and the use of the oven and developed baking into one of the first large-scale food production industries.\" By 4000 BC, wheat had reached the British Isles and Scandinavia. Wheat likely appeared in China's lower Yellow River around 2600 BC.
From Asia, wheat continued to spread across Europe and to the Americas in the Columbian exchange. In the British Isles, wheat straw (thatch) was used for roofing in the Bronze Age, and was in common use until the late 19th century.
White wheat bread was historically a high status food, but during the nineteenth century it became in Britain an item of mass consumption, displacing oats, barley and rye from diets in the North of the country. It became \"a sign of a high degree of culture\". After 1860, the enormous expansion of wheat production in the United States flooded the world market, lowering prices by 40%, and (along with the expansion of potato growing) made a major contribution to the nutritional welfare of the poor.
Technological advances in soil preparation and seed placement at planting time, use of crop rotation and fertilizers to improve plant growth, and advances in harvesting methods have all combined to promote wheat as a viable crop. When the use of seed drills replaced broadcasting sowing of seed in the 18th century, another great increase in productivity occurred.
Yields of pure wheat per unit area increased as methods of crop rotation were applied to long cultivated land, and the use of fertilizers became widespread. Improved agricultural husbandry has more recently included threshing machines, reaper-binder machines (the 'combine harvester'), tractor-drawn cultivators and planters, and better varieties (see Green Revolution and Norin 10 wheat). Great expansion of wheat production occurred as new arable land was farmed in the Americas and Australia in the 19th and 20th centuries.
Leaves emerge from the shoot apical meristem in a telescoping fashion until the transition to reproduction i.e. flowering. The last leaf produced by a wheat plant is known as the flag leaf. It is denser and has a higher photosynthetic rate than other leaves, to supply carbohydrate to the developing ear. In temperate countries the flag leaf, along with the second and third highest leaf on the plant, supply the majority of carbohydrate in the grain and their condition is paramount to yield formation. Wheat is unusual among plants in having more stomata on the upper (adaxial) side of the leaf, than on the under (abaxial) side. It has been theorised that this might be an effect of it having been domesticated and cultivated longer than any other plant. Winter wheat generally produces up to 15 leaves per shoot and spring wheat up to 9 and winter crops may have up to 35 tillers (shoots) per plant (depending on cultivar).
Wheat roots are among the deepest of arable crops, extending as far down as 2 metres (6 ft 7 in). While the roots of a wheat plant are growing, the plant also accumulates an energy store in its stem, in the form of fructans, which helps the plant to yield under drought and disease pressure, but it has been observed that there is a trade-off between root growth and stem non-structural carbohydrate reserves. Root growth is likely to be prioritised in drought-adapted crops, while stem non-structural carbohydrate is prioritised in varieties developed for countries where disease is a bigger issue.
Depending on variety, wheat may be awned or not awned. Producing awns incurs a cost in grain number, but wheat awns photosynthesise more efficiently than their leaves with regards to water usage, so awns are much more frequent in varieties of wheat grown in hot drought-prone countries than those generally seen in temperate countries. For this reason, awned varieties could become more widely grown due to climate change. In Europe, however, a decline in climate resilience of wheat has been observed.
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.
Wheat has also been the subject of mutation breeding, with the use of gamma, x-rays, ultraviolet light, and sometimes harsh chemicals. The varieties of wheat created through these methods are in the hundreds (going as far back as 1960), more of them being created in higher populated countries such as China. Bread wheat with high grain iron and zinc content has been developed through gamma radiation breeding, and through conventional selection breeding.
Pathogens and this crop are constantly in a process of co-evolution. Spore-producing wheat rusts are substantially adapted towards successful spore propagation, which is essentially to say its R0. These pathogens tend towards high-R0 evolutionary attractors.
The presence of certain versions of wheat genes has been important for crop yields. Genes for the 'dwarfing' trait, first used by Japanese wheat breeders to produce short-stalked wheat, have had a huge effect on wheat yields worldwide, and were major factors in the success of the Green Revolution in Mexico and Asia, an initiative led by Norman Borlaug. Dwarfing genes enable the carbon that is fixed in the plant during photosynthesis to be diverted towards seed production, and they also help prevent the problem of lodging. \"Lodging\" occurs when an ear stalk falls over in the wind and rots on the ground, and heavy nitrogenous fertilization of wheat makes the grass grow taller and become more susceptible to this problem. By 1997, 81% of the developing world's wheat area was planted to semi-dwarf wheats, giving both increased yields and better response to nitrogenous fertilizer. 59ce067264