Wheat
Wheat is a group of wild and domesticated grasses of the genus Triticum. They are cultivated for their cereal grains, which are staple foods around the world. Well-known wheat species and hybrids include the most widely grown common wheat, spelt, durum, emmer, einkorn, and Khorasan or Kamut. The archaeological record suggests that wheat was first cultivated in the regions of the Fertile Crescent around 9600 BC.
Wheat is grown on a larger area of land than any other food crop. World trade in wheat is greater than that of all other crops combined. In 2021, world wheat production was, 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 because of the usefulness of gluten to the food industry.
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. When eaten as the whole grain, wheat is a source of multiple nutrients and dietary fibre. In a small part of the general population, gluten – which comprises most of the protein in wheat – can trigger coeliac disease, noncoeliac gluten sensitivity, gluten ataxia, and dermatitis herpetiformis.
Description
Wheat is a stout grass of medium to tall height. Its stem is jointed and usually hollow, forming a straw. There can be many stems on one plant. It has long narrow leaves, their bases sheathing the stem, one above each joint. At the top of the stem is the flower head, containing some 20 to 100 flowers. Each flower contains both male and female parts. The flowers are wind-pollinated, with over 99% of pollination events being self-pollinations and the rest cross-pollinations. The flower is housed in a pair of small leaflike glumes. The two stamens and stigmas protrude outside the glumes. The flowers are grouped into spikelets, each with between two and six flowers. Each fertilised carpel develops into a wheat grain or berry; botanically a caryopsis fruit, it is often called a seed. The grains ripen to a golden yellow; a head of grain is called an ear.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 leaves on the plant, supply the majority of carbohydrate in the grain; their condition is critical for crop yield. Wheat is unusual in having more stomata on the upper side of the leaf, than on the under side. It has been theorised that this might be an effect of having been cultivated longer than any other plant. Winter wheat generally produces up to 15 leaves per shoot, and spring wheat up to 9; winter crops may have up to 35 tillers per plant.
Wheat roots are among the deepest of arable crops, extending as far down as. While the roots of a wheat plant are growing, the plant accumulates an energy store in its stem, in the form of fructans, which helps the plant to yield under drought and disease pressure, but 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. Producing awns incurs a cost in grain number, but wheat awns photosynthesise more efficiently than leaves with regards to water usage, so awns are much more frequent in varieties of wheat grown in hot drought-prone countries than those in temperate countries. For this reason, awned varieties could become more widespread due to climate change. In Europe, wheat's climate resilience has declined.
History
Domestication
s in West Asia harvested wild wheats for thousands of years before they were domesticated, perhaps as early as 21,000 BC, but they formed a minor component of their diets. In this phase of pre-domestication cultivation, early cultivars were spread around the region and slowly developed the traits that came to characterise their domesticated forms.Repeated harvesting and sowing of the grains of wild grasses led to the creation of domestic strains, as mutant forms of wheat were more amenable to cultivation. In domesticated wheat, grains are larger, and the seeds remain attached to the ear by a toughened rachis during harvesting. In wild strains, a more fragile rachis allows the ear to shatter easily, dispersing 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 involve the loss of the plant's natural seed dispersal mechanisms, highly domesticated strains of wheat cannot survive in the wild.
Wild einkorn wheat grows across Southwest Asia in open parkland and steppe environments. It comprises three distinct races, only one of which, native to Southeast Anatolia, was domesticated. The main feature that distinguishes domestic einkorn from wild is that its ears do not shatter without pressure, making it dependent on humans for dispersal and reproduction. It also tends to have wider grains. Wild einkorn was collected at sites such as Tell Abu Hureyra and Mureybet, but the earliest archaeological evidence for the domestic form comes after in southern Turkey, at Çayönü, Cafer Höyük, and possibly Nevalı Çori. Genetic evidence indicates that it was domesticated in multiple places independently.
Wild emmer wheat is less widespread than einkorn, favouring the rocky basaltic and limestone soils found in the Hilly Flanks of the Fertile Crescent. It is more diverse, with domesticated varieties falling into two major groups: hulled or non-shattering, in which threshing separates the whole spikelet; and free-threshing, where the individual grains are separated. Both varieties probably existed in prehistory, but over time free-threshing cultivars became more common. Wild emmer was first cultivated in the southern Levant, as early as 9600 BC. Genetic studies have found that, like einkorn, it was domesticated in southeastern Anatolia, but only once. The earliest secure archaeological evidence for domestic emmer comes from Çayönü,, where distinctive scars on the spikelets indicated that they came from a hulled domestic variety. Slightly earlier finds have been reported from Tell Aswad in Syria,, but these were identified using a less reliable method based on grain size.
Early farming
Einkorn and emmer are considered two of the founder crops cultivated by the first farming societies in Neolithic West Asia. These communities also cultivated naked wheats and a now-extinct domesticated form of Zanduri wheat, as well as a wide variety of other cereal and non-cereal crops. Wheat was relatively uncommon for the first thousand years of the Neolithic, but became a staple after around 8500 BC. Early wheat cultivation did not demand much labour. Initially, farmers took advantage of wheat's ability to establish itself in annual grasslands by enclosing fields against grazing animals and re-sowing stands after they had been harvested, without the need to systematically remove vegetation or till the soil. They may also have exploited natural wetlands and floodplains to practice décrue farming, sowing seeds in the soil left behind by receding floodwater. It was harvested with stone-bladed sickles. The ease of storing wheat and other cereals led farming households to become gradually more reliant on it over time, especially after they developed individual storage facilities that were large enough to hold more than a year's supply.Wheat grain was stored after threshing, with the chaff removed. It was then processed into flour using ground stone mortars. Bread made from ground einkorn and the tubers of a form of club rush was made as early as 12,400 BC. At Çatalhöyük, both wholegrain wheat and flour was used to prepare bread, porridge and gruel. Apart from food, wheat may also have been important to Neolithic societies as a source of straw, which could be used for fuel, wicker-making, or wattle and daub construction.
Spread
Domestic wheat was quickly spread to regions where its wild ancestors did not grow naturally. Emmer was introduced to Cyprus as early as 8600 BC and einkorn ; emmer reached Greece 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 was also cultivated in India around 3500 BC. Wheat likely appeared in China's lower Yellow River around 2600 BC.The oldest evidence for hexaploid wheat is through DNA analysis of wheat seeds from around 6400–6200 BC at Çatalhöyük. the earliest known wheat with sufficient gluten for yeasted breads is from a granary at Assiros in Macedonia dated to 1350 BC. Wheat continued to spread across Europe and to the Americas in the Columbian exchange. In the British Isles, wheat straw was used for roofing in the Bronze Age, remaining 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. After 1860, the expansion of wheat production in the United States flooded the world market, lowering prices by 40%, and made a major contribution to the nutritional welfare of the poor.