Wheat is grown on more land area than any other food crop (220.7 million hectares or 545 million acres in 2021). World trade in wheat is greater than for all other crops combined. In 2021, world wheat production was 771 million
tonnes (850 million short tons), making it the second most-produced cereal after
maize (known as corn in the US and Australia; wheat is often called corn in other countries). 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 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 flower, which is
wind-pollinated, is housed in a pair of small leaflike
glumes. The two (male)
stamens and (female)
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 fruit, it is often called a seed. The grains ripen to a golden yellow; a head of grain is called an ear.[4]
Leaves emerge from the shoot apical
meristem in a telescoping fashion until the transition to reproduction i.e. flowering.[5] 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.[6][7] Wheat is unusual among plants in having more
stomata on the upper (
adaxial) side of the leaf, than on the under (
abaxial) side.[8] It has been theorised that this might be an effect of it having been
domesticated and cultivated longer than any other plant.[9]Winter wheat generally produces up to 15 leaves per shoot and spring wheat up to 9[10] and winter crops may have up to 35
tillers (shoots) per plant (depending on cultivar).[10]
Wheat
roots are among the deepest of arable crops, extending as far down as 2 metres (6 ft 7 in).[11] While the roots of a wheat plant are growing, the plant also accumulates an energy store in its stem, in the form of
fructans,[12] which helps the plant to yield under drought and disease pressure,[13] 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.[14]
Depending on variety, wheat may be
awned or not awned. Producing awns incurs a cost in grain number,[15] but wheat awns photosynthesise more efficiently than their leaves with regards to water usage,[16] 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.[17]
Hunter-gatherers in West Asia harvested wild wheats for thousands of years before they were
domesticated,[18] perhaps as early as 21,000 BC,[19] but they formed a minor component of their diets.[20] 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.[21]
Repeated harvesting and sowing of the grains of
wild grasses led to the creation of domestic strains, as mutant forms ('sports') of wheat were more amenable to cultivation. In domesticated wheat, grains are larger, and the seeds (inside the
spikelets) remain attached to the ear by a toughened
rachis during harvesting.[22] In wild strains, a more fragile rachis allows the ear to
shatter easily, dispersing the spikelets.[23] 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.[24]
Wild
einkorn wheat (T. monococcum subsp. boeoticum) grows across Southwest Asia in open
parkland and
steppe environments.[25] It comprises three distinct
races, only one of which, native to
Southeast Anatolia, was domesticated.[26] 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.[25] It also tends to have wider grains.[25] Wild einkorn was collected at sites such as
Tell Abu Hureyra (
c. 10,700–9000 BC) and
Mureybet (
c. 9800–9300 BC), but the earliest archaeological evidence for the domestic form comes after
c. 8800 BC in southern Turkey, at
Çayönü,
Cafer Höyük, and possibly
Nevalı Çori.[25] Genetic evidence indicates that it was domesticated in multiple places independently.[26]
Wild
emmer wheat (T. turgidum subsp. dicoccoides) is less widespread than einkorn, favouring the rocky
basaltic and
limestone soils found in the
hilly flanks of the Fertile Crescent.[25] 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.[25] Wild emmer was first cultivated in the southern
Levant, as early as 9600 BC.[27][28] Genetic studies have found that, like einkorn, it was domesticated in southeastern Anatolia, but only once.[26][29] The earliest secure archaeological evidence for domestic emmer comes from Çayönü,
c. 8300–7600 BC, where distinctive scars on the spikelets indicated that they came from a hulled domestic variety.[25] Slightly earlier finds have been reported from
Tell Aswad in Syria,
c. 8500–8200 BC, but these were identified using a less reliable method based on grain size.[25]
Early farming
Einkorn and emmer are considered two of the
founder crops cultivated by the first farming societies in
Neolithic West Asia.[25] These communities also cultivated naked wheats (T. aestivum and T. durum) and a now-extinct domesticated form of
Zanduri wheat (T. timopheevii),[30] as well as a wide variety of other cereal and non-cereal crops.[31] Wheat was relatively uncommon for the first thousand years of the Neolithic (when
barley predominated), but became a staple after around 8500 BC.[31] 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.[32] They may also have exploited natural wetlands and floodplains to practice
décrue farming, sowing seeds in the soil left behind by receding floodwater.[33][34][35] It was harvested with
stone-bladedsickles.[36] 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.[37]
Wheat grain was stored after
threshing, with the
chaff removed.[37] It was then processed into flour using
ground stonemortars.[38]Bread made from ground einkorn and the tubers of a form of
club rush (Bolboschoenus glaucus) was made as early as 12,400 BC.[39] At
Çatalhöyük (
c. 7100–6000 BC), both wholegrain wheat and flour was used to prepare bread,
porridge and
gruel.[40][41] 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.[42]
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
c. 7500 BC;[43][44] emmer reached
Greece by 6500 BC,
Egypt shortly after 6000 BC, and
Germany and
Spain by 5000 BC.[45] "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."[46] By 4000 BC, wheat had reached the
British Isles and
Scandinavia.[47][48][49] Wheat likely appeared in
China's lower
Yellow River around 2600 BC.[50]
The oldest evidence for
hexaploid wheat has been confirmed through
DNA analysis of wheat seeds, dating to around 6400–6200 BC, recovered from
Çatalhöyük.[51] As of 2023,[update] the earliest known wheat with sufficient gluten for yeasted breads was found in a granary at
Assiros in
Macedonia dated to 1350 BC.[52] From the
Middle East, 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 remained in common use until the late 19th century.[53][54] 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".[55] 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.[56]
Sumeriancylinder seal impression dating to
c. 3200 BC showing an ensi and his acolyte feeding a sacred herd wheat stalks;
Ninurta was an agricultural deity and, in a poem known as the "Sumerian Georgica", he offers detailed advice on farming
Traditional wheat harvesting in Madhya Pradesh, 2012
Evolution
Phylogeny
Some wheat species are
diploid, with two sets of
chromosomes, but many are stable
polyploids, with four sets of chromosomes (
tetraploid) or six (
hexaploid).[57]Einkorn wheat (Triticum monococcum) is diploid (AA, two complements of seven chromosomes, 2n=14).[58] Most tetraploid wheats (e.g.
emmer and
durum wheat) are derived from
wild emmer, T. dicoccoides. Wild emmer is itself the result of a hybridization between two diploid wild grasses, T. urartu and a wild goatgrass such as Ae. speltoides.[59] The hybridization that formed wild emmer (AABB, four complements of seven chromosomes in two groups, 4n=28) occurred in the wild, long before domestication, and was driven by
natural selection. Hexaploid wheats evolved in farmers' fields as wild emmer hybridized with another goatgrass, Ae. squarrosa or Ae. tauschii, to make the
hexaploid wheats including
bread wheat.[57][60]
A 2007
molecular phylogeny of the wheats gives the following not fully-resolved
cladogram of major cultivated species; the large amount of hybridisation makes resolution difficult. Markings like "6N" indicate the degree of
polyploidy of each species:[57]
During 10,000 years of cultivation, numerous forms of wheat, many of them
hybrids, have developed under a combination of
artificial and
natural selection. This complexity and diversity of status has led to much confusion in the naming of wheats.[61][62]
Major species
Hexaploid species (6N)
Common wheat or bread wheat (T. aestivum) – The most widely cultivated species in the world.[63]
Spelt (T. spelta) – Another species largely replaced by bread wheat, but in the 21st century grown, often organically, for
artisanal bread and pasta.[64]
Tetraploid species (4N)
Durum (T. durum) – A wheat widely used today, and the second most widely cultivated wheat.[63]
Emmer (T. turgidum subsp. dicoccum and T. t. conv. durum) – A species cultivated in
ancient times, derived from wild emmer, T. dicoccoides, but no longer in widespread use.[65]
Khorasan or Kamut (T. turgidum ssp. turanicum, also called T. turanicum) is an ancient grain type; Khorasan is a historical region in modern-day Afghanistan and the northeast of Iran. The grain is twice the size of modern wheat and has a rich nutty flavor.[66]
Diploid species (2N)
Einkorn (T. monococcum). Domesticated from wild einkorn, T. boeoticum, at the same time as emmer wheat.[67]
Hulled versus free-threshing species
The four wild species of wheat, along with the domesticated varieties
einkorn,[68] emmer[69] and
spelt,[70] 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. Hulled wheats are often stored as spikelets because the toughened glumes give good protection against pests of stored grain.[68] 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.[71]
As a food
Naming of grain classes
Wheat grain classes are named by color, season, and hardness.[72] The classes used in the
United States are:[73][74]
Durum – Hard, translucent, light-colored grain used to make
semolina flour for pasta and
bulghur; high in protein, specifically, gluten protein.[73][74]
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 on the
Minneapolis Grain Exchange.[73][74]
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 on the
Kansas City Board of Trade. Many varieties grown from Kansas south are descendant from a variety known as "turkey red", which was brought to Kansas by
Mennonite immigrants from Russia.[73][74][75]Marquis wheat was developed to prosper in the shorter growing season in Canada, and is grown as far south as southern Nebraska.[76]
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 on the
Chicago Board of Trade.[73][74]
Hard White – Hard, light-colored, opaque, chalky, medium-protein wheat planted in dry, temperate areas. Used for bread and brewing.[73][74]
Soft White – Soft, light-colored, very low protein wheat grown in temperate moist areas. Used for pie crusts and pastry.[73][74]
Wheat is a significant source of
vegetable proteins in human food, having a relatively high protein content compared to other major cereals.[85] However, wheat proteins have a low quality for human nutrition, according to the
DIAAS protein quality evaluation method.[86][87] Though they contain adequate amounts of the other essential amino acids, at least for adults, wheat proteins are deficient in the
essential amino acidlysine.[84][88] Because the proteins present in the wheat
endosperm (gluten proteins) are particularly poor in lysine,
white flours are more deficient in lysine compared with whole grains.[84] Significant efforts in plant breeding are made to develop lysine-rich wheat varieties, without success, as of 2017[update].[89] Supplementation with proteins from other food sources (mainly
legumes) is commonly used to compensate for this deficiency,[90] since the limitation of a single essential amino acid causes the others to break down and become excreted, which is especially important during growth.[84]
Health advisories
Consumed worldwide by billions of people, wheat is a significant food for human nutrition, particularly in the
least developed countries where wheat products are primary foods.[84][91] When eaten as the
whole grain, wheat supplies multiple nutrients and
dietary fiber recommended for children and adults.[83][84][92][93]
In genetically susceptible people, wheat gluten can trigger
coeliac disease.[82][94] Coeliac disease affects about 1% of the general population in
developed countries.[94][95] The only known effective treatment is a strict lifelong
gluten-free diet.[94] While coeliac disease is caused by a reaction to wheat proteins, it is not the same as a
wheat allergy.[94][95] Other diseases
triggered by eating wheat are
non-coeliac gluten sensitivity[95][96] (estimated to affect 0.5% to 13% of the general population[97]),
gluten ataxia, and
dermatitis herpetiformis.[96]
Certain short-chain carbohydrates present in wheat, known as
FODMAPs (mainly
fructose polymers), may be the cause of non-coeliac gluten sensitivity. As of 2019[update], reviews have concluded that FODMAPs only explain certain gastrointestinal symptoms, such as
bloating, but not the
extra-digestive symptoms that people with non-coeliac gluten sensitivity may develop health disorders.[98][99][100]
Other wheat proteins, amylase-trypsin inhibitors, have been identified as the possible activator of the
innate immune system in coeliac disease and non-coeliac gluten sensitivity.[99][100] These proteins are part of the plant's natural defense against insects and may cause intestinal
inflammation in humans.[99][101]
Wheat's share (brown) of world crop production fell in the 21st century.
In 2022, world wheat production was 808.4 million tonnes, led by China, India, and Russia which collectively provided 43.22% of the world total.[104] As of 2019[update],
the largest exporters were Russia (32 million tonnes), United States (27), Canada (23) and France (20), while the largest importers were Indonesia (11 million tonnes), Egypt (10.4) and Turkey (10.0).[105]
In 2021, wheat was grown on 220.7 million hectares or 545 million acres worldwide, more than any other food crop.[106]
World trade in wheat is greater than for all other crops combined.[107]
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
westernization of diets.[84][108]
Historical factors
Wheat became a central agriculture endeavor in the worldwide
British Empire in the 19th century, and remains of great importance in Australia, Canada and India.[110] In Australia, with vast lands and a limited work force, expanded production depended on technological advances, especially regarding irrigation and machinery. By the 1840s there were 900 growers in
South Australia. They used "Ridley's Stripper", to remove the heads of grain, a reaper-harvester perfected by
John Ridley in 1843.[111] In Canada, modern farm implements made large scale wheat farming possible from the late 1840s. By 1879,
Saskatchewan was the center, followed by
Alberta,
Manitoba and
Ontario, as the spread of railway lines allowed easy exports to Britain. By 1910, wheat made up 22% of Canada's exports, rising to 25% in 1930 despite the sharp decline in prices during the worldwide
Great Depression.[112] Efforts to expand wheat production in South Africa, Kenya and India were stymied by low yields and disease. However, by 2000 India had become the second largest producer of wheat in the world.[113] In the 19th century the American wheat frontier moved rapidly westward. By the 1880s 70% of American exports went to British ports. The first successful
grain elevator was built in Buffalo in 1842.[114] The cost of transport fell rapidly. In 1869 it cost 37 cents to transport a bushel of wheat from
Chicago to
Liverpool. In 1905 it was 10 cents.[115]
In the 20th century, global wheat output expanded by about 5-fold, but until about 1955 most of this reflected increases in wheat crop area, with lesser (about 20%) increases in crop yields per unit area. After 1955 however, there was a ten-fold increase in the rate of wheat yield improvement per year, and this became the major factor allowing global wheat production to increase. Thus technological innovation and scientific crop management with
synthetic nitrogen fertilizer, irrigation and wheat breeding were the main drivers of wheat output growth in the second half of the century. There were some significant decreases in wheat crop area, for instance in North America.[116] Better seed storage and germination ability (and hence a smaller requirement to retain harvested crop for next year's seed) is another 20th-century technological innovation. In Medieval England, farmers saved one-quarter of their wheat harvest as seed for the next crop, leaving only three-quarters for food and feed consumption. By 1999, the global average seed use of wheat was about 6% of output.[117]
In the 21st century, rising temperatures associated with
global warming are reducing wheat yield in several locations.[118]
Peak wheat is the concept that
agricultural production, due to its high use of water and energy inputs,[119] is subject to the
same profile as oil and other
fossil fuel production.[120][121][122] The central tenet is that a point is reached, the "peak", beyond which agricultural production plateaus and does not grow any further,[123] and may even go into permanent decline.
Based on current
supply and demand factors for agricultural
commodities (e.g., changing diets in the
emerging economies,
biofuels, declining acreage under irrigation, growing
global population, stagnant
agricultural productivity growth),[124] some commentators are predicting a long-term annual production shortfall of around 2% which, based on the highly inelastic
demand curve for food crops, could lead to sustained price increases in excess of 10% a year – sufficient to double crop prices in seven years.[125][126][127]
According to the
World Resources Institute, global per capita food production has been increasing substantially for the past several decades.[128]
Agronomy
Growing wheat
Wheat is an
annual crop. It can be planted in autumn and harvested in early summer as
winter wheat in climates that are not too severe, or planted in spring and harvested in autumn as spring wheat. It is normally planted after
tilling the soil by
ploughing and then
harrowing to kill weeds and create an even surface. The seeds are then scattered on the surface, or
drilled into the soil in rows. Winter wheat lies dormant during a winter freeze. It needs to develop to a height of 10 to 15 cm before the cold intervenes, so as to be able to survive the winter; it requires a period with the temperature at or near freezing, its
dormancy then being broken by the thaw or rise in temperature. Spring wheat does not undergo dormancy. Wheat requires a deep
soil, preferably a
loam with organic matter, and available minerals including soil nitrogen, phosphorus, and potassium. An acid and
peaty soil is not suitable. Wheat needs some 30 to 38 cm of rain in the growing season to form a good crop of grain.[129]
The farmer may intervene while the crop is growing to add
fertilizer, water by
irrigation, or pesticides such as
herbicides to kill broad-leaved weeds or
insecticides to kill insect pests. The farmer may assess soil minerals, soil water, weed growth, or the arrival of pests to decide timely and cost-effective corrective actions, and crop ripeness and water content to select the right moment to harvest. Harvesting involves
reaping, cutting the stems to gather the crop; and
threshing, breaking the ears to release the grain; both steps are carried out by a
combine harvester. The grain is then dried so that it can be stored safe from
mould fungi.[129]
Crop development
Wheat normally needs between 110 and 130 days between sowing and harvest, depending upon climate, seed type, and soil conditions. Optimal crop management requires that the farmer have a detailed understanding of each stage of development in the growing plants. In particular, spring
fertilizers,
herbicides,
fungicides, and
growth regulators are typically applied only at specific stages of plant development. For example, it is currently recommended that the second application of nitrogen is best done when the ear (not visible at this stage) is about 1 cm in size (Z31 on
Zadoks scale). Knowledge of stages is also important to identify periods of higher risk from the climate. Farmers 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 so 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.[130] For example, the stage of pollen formation from the mother cell, and the stages between
anthesis and maturity, are susceptible to high temperatures, and this adverse effect is made worse by water stress.[131]
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 land that had long been in cultivation, and the use of fertilizers became widespread.[132]
In addition to gaps in farming system technology and knowledge, some large wheat grain-producing countries have significant losses after harvest at the farm and because of poor roads, inadequate storage technologies, inefficient supply chains and farmers' inability to bring the produce into retail markets dominated by small shopkeepers. Some 10% of total wheat production is lost at farm level, another 10% is lost because of poor storage and road networks, and additional amounts are lost at the retail level.[138]
In the
Punjab region of the Indian subcontinent, as well as North China, irrigation has been a major contributor to increased grain output. More widely over the last 40 years, a massive increase in fertilizer use together with the increased availability of semi-dwarf varieties in developing countries, has greatly increased yields per hectare.[139] In developing countries, use of (mainly nitrogenous) fertilizer increased 25-fold in this period. However, farming systems rely on much more than fertilizer and breeding to improve productivity. A good illustration of this is Australian wheat growing in the southern winter cropping zone, where, despite low rainfall (300 mm), wheat cropping is successful even with relatively little use of nitrogenous fertilizer. This is achieved by crop rotation with leguminous pastures. The inclusion of a
canola crop in the rotations has boosted wheat yields by a further 25%.[140] In these low rainfall areas, better use of available soil-water (and better control of soil erosion) is achieved by retaining the stubble after harvesting and by minimizing tillage.[141]
Field ready for harvesting
Combine harvester cuts the wheat stems,
threshes the wheat, crushes the
chaff and blows it across the field, and loads the grain onto a tractor trailer.
Pests and diseases
Pests[142] – or pests and diseases, depending on the definition – consume 21.47% of the world's wheat crop annually.[143]
There are many wheat diseases, mainly caused by fungi, bacteria, and
viruses.[144]Plant breeding to develop new disease-resistant varieties, and sound crop management practices are important for preventing disease. Fungicides, used to prevent the significant crop losses from fungal disease, can be a significant variable cost in wheat production. Estimates of the amount of wheat production lost owing to plant diseases vary between 10 and 25% in Missouri.[145] A wide range of organisms infect wheat, of which the most important are viruses and fungi.[146]
The main wheat-disease categories are:
Seed-borne diseases: these include seed-borne scab, seed-borne Stagonospora (previously known as Septoria),
common bunt (stinking smut), and
loose smut. These are managed with
fungicides.[147]
A historically significant disease of cereals including wheat, though commoner in
rye is
ergot; it is unusual among plant diseases in also causing sickness in humans who ate grain contaminated with the fungus involved, Claviceps purpurea.[151]
Animal pests
Among insect pests of wheat is the
wheat stem sawfly,
a chronic pest in the Northern Great Plains of the United States and in the
Canadian Prairies.[152]
Wheat is the food plant of the
larvae of some
Lepidoptera (
butterfly and
moth) species including
the flame,
rustic shoulder-knot,
setaceous Hebrew character and
turnip moth. Early in the season, many species of birds and rodents feed upon wheat crops. These animals can cause significant damage to a crop by digging up and eating newly planted seeds or young plants. They can also damage the crop late in the season by eating the grain from the mature spike. Recent post-harvest losses in cereals amount to billions of dollars per year in the United States alone, and damage to wheat by various borers, beetles and weevils is no exception.[153] Rodents can also cause major losses during storage, and in major grain growing regions, field mice numbers can sometimes build up explosively to plague proportions because of the ready availability of food.[154] To reduce the amount of wheat lost to post-harvest pests,
Agricultural Research Service scientists have developed an "insect-o-graph", which can detect insects in wheat that are not visible to the naked eye. The device uses electrical signals to detect the insects as the wheat is being milled. The new technology is so precise that it can detect 5–10 infested seeds out of 30,000 good ones.[155]
Breeding objectives
In traditional agricultural systems, wheat populations consist of
landraces, informal farmer-maintained populations that often maintain high levels of morphological diversity. Although landraces of wheat are no longer extensively 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.[156]
Major breeding objectives include high
grain yield, good quality,
disease- and insect resistance and tolerance to abiotic stresses, including mineral, moisture and heat tolerance.[157][158] Wheat has been the subject of
mutation breeding, with the use of
gamma-,
x-rays,
ultraviolet light (collectively, radiation breeding), 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.[157] Bread wheat with high grain iron and zinc content has been developed through gamma radiation breeding,[159] and through conventional selection breeding.[160] International wheat breeding is led by the International Maize and Wheat Improvement Center in Mexico.
ICARDA is another major public sector international wheat breeder, but it was forced to relocate from Syria to Lebanon in the
Syrian Civil War.[161]
Pathogens and wheat are in a constant process of
coevolution.[162]Spore-producing wheat rusts are substantially
adapted towards successful spore propagation, which is essentially to say its
R0.[162] These pathogens tend towards high-R0evolutionary attractors.[162]
For higher yields
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
Norin 10 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.[163] 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.[164] "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.[165] 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.[166]
T. turgidum subsp. polonicum, known for its longer
glumes and grains, has been bred into main wheat lines for its grain size effect, and likely has contributed these traits to Triticum petropavlovskyi and the Portuguese
landrace group Arrancada.[167] As with many plants,
MADS-box influences flower development, and more specifically, as with other agricultural Poaceae, influences yield. Despite that importance, as of 2021[update] little research has been done into MADS-box and other such spikelet and flower genetics in wheat specifically.[167]
The world record wheat yield is about 17
tonnes per
hectare (15,000 pounds per acre), reached in New Zealand in 2017.[168] A project in the UK, led by
Rothamsted Research has aimed to raise wheat yields in the country to 20 t/ha (18,000 lb/acre) by 2020, but in 2018 the UK record stood at 16 t/ha (14,000 lb/acre), and the average yield was just 8 t/ha (7,100 lb/acre).[169][170]
For disease resistance
Wild grasses in the genus Triticum and related genera, and grasses such as
rye have been a source of many disease-resistance traits for cultivated wheat
breeding since the 1930s.[171] Some
resistance genes have been identified against Pyrenophora tritici-repentis, especially races 1 and 5, those most problematic in
Kazakhstan.[172]Wild relative, Aegilops tauschii is the source of several genes effective against
TTKSK/Ug99 - Sr33, Sr45, Sr46, and SrTA1662 - of which Sr33 and SrTA1662 are the work of Olson et al., 2013, and Sr45 and Sr46 are also briefly reviewed therein.[173]
Lr34 is widely deployed in cultivars due to its abnormally broad effectiveness, conferring resistance against
leaf- and
stripe-rusts, and
powdery mildew.[175]An important quantitative resistance gene, Lr34, has been isolated and used intensively in wheat cultivation worldwide; it provides a novel resistance mechanism.[176][177] Krattinger et al. 2009 find Lr34 to be an
ABC transporter, and conclude that this is the probable reason for its effectiveness[175][178] and the reason that it produces a 'slow rusting'/
adult resistance phenotype.[178]
In 2003 the first resistance genes against fungal diseases in wheat were isolated.[181][182] In 2021, novel resistance genes were identified in wheat against
powdery mildew and
wheat leaf rust.[183][184]
Modified resistance genes have been tested in transgenic wheat and barley plants.[185]
To create hybrid vigor
Because wheat self-pollinates, creating
hybrid seed to provide the possible benefits of
heterosis, hybrid vigor (as in the familiar F1 hybrids of maize), is extremely labor-intensive; the high cost of hybrid wheat seed relative to its moderate benefits have kept farmers from adopting them widely[186][187] despite nearly 90 years of effort.[188][156] 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 United States and South Africa.[189]
Synthetic hexaploids made by crossing the wild goatgrass wheat ancestor Aegilops tauschii,[190] and other Aegilops,[191] and various durum wheats are now being deployed, and these increase the genetic diversity of cultivated wheats.[192][193][194]
For gluten content
Modern bread wheat varieties have been
cross-bred to contain greater amounts of gluten,[195] which affords significant advantages for improving the quality of breads and pastas from a functional point of view.[196] However, a 2020 study that grew and analyzed 60 wheat cultivars from between 1891 and 2010 found no changes in albumin/globulin and gluten contents over time. "Overall, the harvest year had a more significant effect on protein composition than the cultivar. At the protein level, we found no evidence to support an increased
immunostimulatory potential of modern winter wheat."[197]
For water efficiency
Stomata (or leaf pores) are involved in both uptake of carbon dioxide gas from the atmosphere and water vapor losses from the leaf due to water
transpiration. Basic physiological investigation of these gas exchange processes has yielded carbon
isotope based method used for breeding wheat varieties with improved water-use efficiency. These varieties can improve crop productivity in rain-fed dry-land wheat farms.[198]
In 2010, 95% of the genome of Chinese Spring line 42 wheat was decoded.[203] This genome was released in a basic format for scientists and plant breeders to use but was not fully annotated.[204] In 2012, an essentially complete gene set of bread wheat was published.[205]Random shotgun libraries of total DNA and cDNA from the T. aestivum cv. Chinese Spring (CS42) were sequenced to generate 85 Gb of sequence (220 million reads) and identified between 94,000 and 96,000 genes.[205] In 2018, a more complete Chinese Spring genome was released by a different team.[206] In 2020, 15 genome sequences from various locations and varieties around the world were reported, with examples of their own use of the sequences to localize particular insect and disease resistance factors.[201]Wheat Blast Resistance is controlled by
R genes which are highly race-specific.[150]
Triticum aestivum EDR1 (TaEDR1) (the EDR1 gene, which inhibits Bmt resistance) has been
knocked out by Zhang et al. 2017 to improve that resistance[207]
As of 2021[update] these examples illustrate the rapid deployment and results that CRISPR/Cas9 has shown in wheat disease resistance improvement.[207]
In art
The Dutch artist
Vincent van Gogh created the series Wheat Fields between 1885 and 1890, consisting of dozens of paintings made mostly in different parts of rural France. They depict wheat crops, sometimes with farm workers, in varied seasons and styles, sometimes green, sometimes at harvest. Wheatfield with Crows was one of his last paintings, and is considered to be among his greatest works.[208][209]
In 1967, the American artist
Thomas Hart Benton made his oil on wood painting Wheat, showing a row of uncut wheat plants, occupying almost the whole height of the painting, between rows of freshly-cut stubble. The painting is held by the
Smithsonian American Art Museum.[210]
In 1982, the American conceptual artist
Agnes Denes grew a two-acre field of wheat at
Battery Park, Manhattan. The
ephemeral artwork has been described as an act of protest. The harvested wheat was divided and sent to 28 world cities for an exhibition entitled "The International Art Show for the End of World Hunger".[211]
^Pajević, Slobodanka; Krstić, Borivoj; Stanković, Živko; Plesničar, Marijana; Denčić, Srbislav (1999). "Photosynthesis of Flag and Second Wheat Leaves During Senescence". Cereal Research Communications. 27 (1/2): 155–162.
doi:
10.1007/BF03543932.
JSTOR23786279.
^Araus, J. L.; Tapia, L.; Azcon-Bieto, J.; Caballero, A. (1986). "Photosynthesis, Nitrogen Levels, and Dry Matter Accumulation in Flag Wheat Leaves During Grain Filling". Biological Control of Photosynthesis. pp. 199–207.
doi:
10.1007/978-94-009-4384-1_18.
ISBN978-94-010-8449-9.
^Singh, Sarvjeet; Sethi, G.S. (1995). "Stomatal Size, Frequency and Distribution in Triticum Aestivum, Secale Cereale and Their Amphiploids". Cereal Research Communications. 23 (1/2): 103–108.
JSTOR23783891.
^Duwayri, Mahmud (1984). "Effect of flag leaf and awn removal on grain yield and yield components of wheat grown under dryland conditions". Field Crops Research. 8: 307–313.
doi:
10.1016/0378-4290(84)90077-7.
^Scott, James C. (2017). "The Domestication of Fire, Plants, Animals, and ... Us".
Against the Grain: A Deep History of the Earliest States. New Haven: Yale University Press. p. 66.
ISBN978-0-3002-3168-7. Retrieved 19 March 2023. The general problem with farming — especially plough agriculture — is that it involves so much intensive labor. One form of agriculture, however, eliminates most of this labor: 'flood-retreat' (also known as décrue or recession) agriculture. In flood-retreat agriculture, seeds are generally broadcast on the fertile silt deposited by an annual riverine flood.
^Graeber, David; Wengrow, David (2021). The dawn of everything: a new history of humanity. London: Allen Lane. p. 235.
ISBN978-0-241-40242-9.
^Long, Tengwen; Leipe, Christian; Jin, Guiyun; Wagner, Mayke; Guo, Rongzhen; et al. (2018). "The early history of wheat in China from 14C dating and Bayesian chronological modelling". Nature Plants. 4 (5): 272–279.
doi:
10.1038/s41477-018-0141-x.
PMID29725102.
S2CID19156382.
^Nelson, Scott Reynolds (2022). Oceans of Grain: How American Wheat Remade the World. Basic Books. pp. 3–4.
ISBN978-1-5416-4646-9.
^
abcdGolovnina, K. A.; Glushkov, S. A.; Blinov, A. G.; Mayorov, V. I.; Adkison, L. R.; Goncharov, N. P. (12 February 2007). "Molecular phylogeny of the genus Triticum L". Plant Systematics and Evolution. 264 (3–4). Springer: 195–216.
Bibcode:
2007PSyEv.264..195G.
doi:
10.1007/s00606-006-0478-x.
S2CID39102602.
^
abBelderok, Robert 'Bob'; Mesdag, Hans; Donner, Dingena A. (2000). Bread-Making Quality of Wheat. Springer. p. 3.
ISBN978-0-7923-6383-5.
^Khlestkina, Elena K.; Röder, Marion S.; Grausgruber, Heinrich; Börner, Andreas (2006). "A DNA fingerprinting-based taxonomic allocation of Kamut wheat". Plant Genetic Resources. 4 (3): 172–180.
doi:
10.1079/PGR2006120.
S2CID86510231.
^Anderson, Patricia C. (1991). "Harvesting of Wild Cereals During the Natufian as seen from Experimental Cultivation and Harvest of Wild Einkorn Wheat and Microwear Analysis of Stone Tools". In Bar-Yosef, Ofer (ed.). Natufian Culture in the Levant. International Monographs in Prehistory. Ann Arbor, Michigan: Berghahn Books. p. 523.
^
abPotts, D.T. (1996) Mesopotamia Civilization: The Material Foundations Cornell University Press. p. 62.
ISBN0-8014-3339-8.
^Nevo, Eviatar; Korol, A.B.; Beiles, A.; Fahima, T. (2002) Evolution of Wild Emmer and Wheat Improvement: Population Genetics, Genetic Resources, and Genome.... Springer. p. 8.
ISBN3-540-41750-8.
^"Field Crop Information". College of Agriculture and Bioresources, University of Saskatchewan. Archived from
the original on 18 October 2023. Retrieved 10 July 2023.
^Bridgwater, W. & Beatrice Aldrich. (1966) "Wheat". The Columbia-Viking Desk Encyclopedia. Columbia University. p. 1959.
^National Academies of Sciences, Engineering, and Medicine; Health and Medicine Division; Food and Nutrition Board; Committee to Review the Dietary Reference Intakes for Sodium and Potassium (2019). Oria, Maria; Harrison, Meghan; Stallings, Virginia A. (eds.).
Dietary Reference Intakes for Sodium and Potassium. The National Academies Collection: Reports funded by National Institutes of Health. Washington (DC): National Academies Press (US).
ISBN978-0-309-48834-1.
PMID30844154.{{
cite book}}: CS1 maint: multiple names: authors list (
link)
^
ab"Whole Grain Fact Sheet". European Food Information Council. 1 January 2009. Archived from
the original on 20 December 2016. Retrieved 6 December 2016.
^
abcd"Celiac disease". World Gastroenterology Organisation Global Guidelines. July 2016. Retrieved 7 December 2016.
^
abc"Definition and Facts for Celiac Disease". The National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, US Department of Health and Human Services, Bethesda, MD. 2016. Retrieved 5 December 2016.
^IFDC, World Fertilizer Prices Soar,
"Archived copy"(PDF). Archived from
the original(PDF) on 9 May 2008. Retrieved 3 March 2009.{{
cite web}}: CS1 maint: archived copy as title (
link)
^Agcapita Farmland Investment Partnership - Peak oil v. Peak Wheat, July 1, 2008,
"Archived copy"(PDF). Archived from
the original(PDF) on 20 March 2009. Retrieved 24 July 2008.{{
cite web}}: CS1 maint: archived copy as title (
link)
^Slafer, G.A.; Satorre, E.H. (1999). Wheat: Ecology and Physiology of Yield Determination. Haworth Press. pp. 322–323.
ISBN1-56022-874-1.
^Saini, H.S.; Sedgley, M.; Aspinall, D. (1984). "Effect of heat stress during floral development on pollen tube growth and ovary anatomy in wheat (Triticum aestivum L.)". Australian Journal of Plant Physiology. 10 (2): 137–144.
doi:
10.1071/PP9830137.
^Brown, L. R. (30 October 1970). "Nobel Peace Prize: developer of high-yield wheat receives award (Norman Ernest Borlaug)". Science. 170 (957): 518–519.
doi:
10.1126/science.170.3957.518.
PMID4918766.
^Gautam, P.; Dill-Macky, R. (2012). "Impact of moisture, host genetics and Fusarium graminearum isolates on Fusarium head blight development and trichothecene accumulation in spring wheat". Mycotoxin Research. 28 (1): 45–58.
doi:
10.1007/s12550-011-0115-6.
PMID23605982.
S2CID16596348.
^Verma, Shailender Kumar; Kumar, Satish; Sheikh, Imran; et al. (3 March 2016). "Transfer of useful variability of high grain iron and zinc from Aegilops kotschyi into wheat through seed irradiation approach". International Journal of Radiation Biology. 92 (3): 132–139.
doi:
10.3109/09553002.2016.1135263.
PMID26883304.
S2CID10873152.