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=== Historical factors ===
=== Historical factors ===

====British Empire and successor states====


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.<ref>Alan Palmer, ''Dictionary of the British Empire and Commonwealth'' (1996) pp 193, 320, 338.</ref> 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 the "Ridley's Stripper", to remove the heads of grain, and the reaper-harvester perfected by [[John Ridley (inventor)|John Ridley]] in 1843.<ref>Annie E. Ridley, ''A Backward Glance: The Story of John Ridley, a Pioneer'' (J. Clarke, 1904). [https://books.google.com/books?id=B44WAAAAYAAJ&dq=john+Ridley+australia+wheat&pg=PP21 online]
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.<ref>Alan Palmer, ''Dictionary of the British Empire and Commonwealth'' (1996) pp 193, 320, 338.</ref> 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 the "Ridley's Stripper", to remove the heads of grain, and the reaper-harvester perfected by [[John Ridley (inventor)|John Ridley]] in 1843.<ref>Annie E. Ridley, ''A Backward Glance: The Story of John Ridley, a Pioneer'' (J. Clarke, 1904). [https://books.google.com/books?id=B44WAAAAYAAJ&dq=john+Ridley+australia+wheat&pg=PP21 online]
</ref> By 1850 South Australia had become the granary for the region; soon wheat farming spread to Victoria and New South Wales, with heavy exports to Great Britain. In Canada modern farm implements made large scale wheat farming possible from the late 1840s on. By the 1879s 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]].<ref>{{Cite journal |last1=Furtan |first1=W. Hartley |last2=Lee |first2=George E. |title=Economic Development of the Saskatchewan Wheat Economy |date=1977 |url=https://onlinelibrary.wiley.com/doi/10.1111/j.1744-7976.1977.tb02882.x |journal=Canadian Journal of Agricultural Economics|language=en |volume=25 |issue=3 |pages=15–28 |doi=10.1111/j.1744-7976.1977.tb02882.x}}</ref> 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.<ref>{{Cite journal |last1=Joshi |first1=A. K. |last2=Mishra |first2=B. |last3=Chatrath |first3=R. |last4=Ortiz Ferrara |first4=G. |last5=Singh |first5=Ravi P. |date=2007 |title=Wheat improvement in India: present status, emerging challenges and future prospects |url=https://link.springer.com/10.1007/s10681-007-9385-7 |journal=Euphytica|language=en |volume=157 |issue=3 |pages=431–446 |doi=10.1007/s10681-007-9385-7 |s2cid=38596433 |issn=0014-2336}}</ref>
</ref> By 1850 South Australia had become the granary for the region; soon wheat farming spread to Victoria and New South Wales, with heavy exports to Great Britain. In Canada modern farm implements made large scale wheat farming possible from the late 1840s on. By the 1879s 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]].<ref>{{Cite journal |last1=Furtan |first1=W. Hartley |last2=Lee |first2=George E. |title=Economic Development of the Saskatchewan Wheat Economy |date=1977 |url=https://onlinelibrary.wiley.com/doi/10.1111/j.1744-7976.1977.tb02882.x |journal=Canadian Journal of Agricultural Economics|language=en |volume=25 |issue=3 |pages=15–28 |doi=10.1111/j.1744-7976.1977.tb02882.x}}</ref> 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.<ref>{{Cite journal |last1=Joshi |first1=A. K. |last2=Mishra |first2=B. |last3=Chatrath |first3=R. |last4=Ortiz Ferrara |first4=G. |last5=Singh |first5=Ravi P. |date=2007 |title=Wheat improvement in India: present status, emerging challenges and future prospects |url=https://link.springer.com/10.1007/s10681-007-9385-7 |journal=Euphytica|language=en |volume=157 |issue=3 |pages=431–446 |doi=10.1007/s10681-007-9385-7 |s2cid=38596433 |issn=0014-2336}}</ref> 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.<ref>{{cite book |last1=Otter |first1=Chris |title=Diet for a large planet |date=2020 | publisher=[[University of Chicago Press]] |location=USA |isbn=978-0-226-69710-9 |page=51 }}</ref> 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.<ref>{{cite book |last1=Otter |first1=Chris |title=Diet for a large planet |date=2020 | publisher=[[University of Chicago Press]] |location=USA |isbn=978-0-226-69710-9 |page=69 }}</ref>

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.<ref>{{cite book |last1=Otter |first1=Chris |title=Diet for a large planet |date=2020 | publisher=[[University of Chicago Press]] |location=USA |isbn=978-0-226-69710-9 |page=51 }}</ref> 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.<ref>{{cite book |last1=Otter |first1=Chris |title=Diet for a large planet |date=2020 | publisher=[[University of Chicago Press]] |location=USA |isbn=978-0-226-69710-9 |page=69 }}</ref>

====20th century====

⚫
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 [[Haber process|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.<ref>See Chapter 1, Slafer GA, Satorre EH (1999) ''Wheat: Ecology and Physiology of Yield Determination'' Haworth Press Technology & Industrial {{ISBN|1-56022-874-1}}.</ref>

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.


⚫
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 [[Haber process|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.<ref>See Chapter 1, Slafer GA, Satorre EH (1999) ''Wheat: Ecology and Physiology of Yield Determination'' Haworth Press Technology & Industrial {{ISBN|1-56022-874-1}}.</ref> 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.
====21st century====


Several factors are currently slowing the rate of global expansion of wheat production: population growth rates are falling while wheat yields continue to rise. There is evidence, however, that rising temperatures associated with [[Global warming|climate change]] are reducing wheat yield in several locations.<ref>{{Cite journal|last1=Asseng|first1=S.|last2=Ewert|first2=F.|last3=Martre|first3=P.|last4=Rötter|first4=R. P.|last5=Lobell|first5=D. B.|last6=Cammarano|first6=D.|last7=Kimball|first7=B. A.|last8=Ottman|first8=M. J.|last9=Wall|first9=G. W.|last10=White|first10=J. W.|last11=Reynolds|first11=M. P.|date=2015|title=Rising temperatures reduce global wheat production|journal=[[Nature Climate Change]]|language=en|volume=5|issue=2|pages=143–147|doi=10.1038/nclimate2470|bibcode=2015NatCC...5..143A|issn=1758-678X|url=http://eprints.whiterose.ac.uk/85540/1/Main_Asseng_2014-9-22.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://eprints.whiterose.ac.uk/85540/1/Main_Asseng_2014-9-22.pdf |archive-date=2022-10-09 |url-status=live}}</ref> In addition, the better economic profitability of other crops such as soybeans and maize, linked with investment in modern genetic technologies, has promoted shifts to other crops.
In the 21st century, several factors are slowing the rate of global expansion of wheat production: population growth rates are falling while wheat yields continue to rise. There is evidence, however, that rising temperatures associated with [[Global warming|climate change]] are reducing wheat yield in several locations.<ref>{{Cite journal|last1=Asseng|first1=S.|last2=Ewert|first2=F.|last3=Martre |first3=P.|last4=Rötter|first4=R. P.|last5=Lobell |first5=D. B.|last6=Cammarano|first6=D.|last7=Kimball|first7=B. A.|last8=Ottman|first8=M. J.|last9=Wall|first9=G. W.|last10=White|first10=J. W.|last11=Reynolds|first11=M. P.|date=2015|title=Rising temperatures reduce global wheat production|journal=[[Nature Climate Change]]|language=en|volume=5|issue=2 |pages=143–147|doi=10.1038/nclimate2470 |bibcode=2015NatCC...5..143A |issn=1758-678X |url=http://eprints.whiterose.ac.uk/85540/1/Main_Asseng_2014-9-22.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://eprints.whiterose.ac.uk/85540/1/Main_Asseng_2014-9-22.pdf |archive-date=2022-10-09 |url-status=live}}</ref> In addition, the better economic profitability of other crops such as soybeans and maize, linked with investment in modern genetic technologies, has promoted shifts to other crops.


=== Farming systems ===
=== Farming systems ===

Revision as of 15:05, 4 October 2023

This article is about the plant. For other uses, see Wheat (disambiguation).

Wheat
Scientific classification Edit this classification
Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Monocots
Clade: Commelinids
Order: Poales
Family: Poaceae
Subfamily: Pooideae
Supertribe: Triticodae
Tribe: Triticeae
Genus: Triticum
L.[1]
Type species
Triticum aestivum

Species[2]
List of Triticum species:

Wheat is a grass widely cultivated for its seed, a cereal grain that is a worldwide staple food.[3][4][5] The many species of wheat together make up the genus Triticum /ˈtrɪtɪkəm/;[6] 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.

Wheat is grown on more land area than any other food crop (220.4 million hectares or 545 million acres, 2014).[7] World trade in wheat is greater than for all other crops combined.[8]

In 2020, world production of wheat was 761 million

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.[11][12]

Wheat is an important source of

vegetable proteins in human food, having a protein content of about 13%, which is relatively high compared to other major cereals[13] but relatively low in protein quality (supplying essential amino acids).[14][15] When eaten as the whole grain, wheat is a source of multiple nutrients and dietary fiber.[11]

In a small part of the general population, gluten – comprising most of wheat protein – can trigger

gluten ataxia, and dermatitis herpetiformis.[16]

Origins

History

Origin and current production area of wheat

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.[17] In wild strains, a more fragile rachis allows the ear to easily shatter and disperse the spikelets.[18] 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

Abu Hureyra in Syria, suggest the domestication of einkorn near the Karacadaǧ Mountains.[21] With the anomalous exception of two grains from Iraq ed-Dubb in Jordan, the earliest carbon-14 date for einkorn wheat remains at Abu Hureyra is 7800 to 7500 years BC.[22]

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.[23]

The cultivation of emmer reached Greece, Cyprus and the Indian subcontinent by 6500 BC, Egypt shortly after 6000 BC, and Germany and Spain by 5000 BC.[24] "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."[25] By 4000 BC, wheat had reached the British Isles and Scandinavia.[26][27][28] Wheat likely appeared in China's lower Yellow River around 2600 BC.[29]

The oldest evidence for

DNA analysis of wheat seeds, dating to around 6400–6200 BC, recovered from Çatalhöyük.[30]

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.[31]

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 was in common use until the late 19th century.[32][33]

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".[34] 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.[35]

  • Sumerian cylinder 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
    Sumerian cylinder 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
  • Threshing of wheat in ancient Egypt
    Threshing of wheat in ancient Egypt
  • Traditional wheat harvesting in Madhya Pradesh, 2012
    Traditional wheat harvesting in Madhya Pradesh, 2012

Phylogeny

Polyploid wheat origins by hybridization and polyploidy[36]

Some wheat species are

hexaploid wheats including bread wheat.[36]

A 2007 molecular phylogeny of the wheats gives the following not fully-resolved cladogram of major cultivated species. Markings like "6N" indicate the degree of polyploidy of each species:[36]

Triticeae

Barley 2N, rye 2N/4N, and other cereals

Wheats

Triticum monococcum (einkorn) 2N

× Aegilotriticum hybrids (Aegilops x Triticum) 6N

Triticum timopheevii (zanduri wheat) and others 4N

Triticum aestivum (common or bread wheat) 6N

Triticum durum/turgidum (durum wheat) 4N

Triticum spelta (spelt) 6N

Triticum turanicum (khorasan wheat) 4N

Triticum dicoccum (emmer) 4N

many other species


Hexaploid species (6N)

  • Common wheat or bread wheat (T. aestivum) – The most widely cultivated species in the world.[38]
  • Spelt (T. spelta) – Another species largely replaced by bread wheat, but in the 21st century grown, often organically, for artisanal bread and pasta.[39]

Tetraploid species (4N)

  • Durum (T. durum) – A wheat widely used today, and the second most widely cultivated wheat.[38]
  • Emmer (T. dicoccum) – A species cultivated in ancient times but no longer in widespread use.[40]
  • 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.[41]

Diploid species (2N)

  • Einkorn (T. monococcum) – A species with wild and cultivated variants. Domesticated at the same time as emmer wheat.[42]

Physiology

Components of the plant

Leaves emerge from the shoot apical

stomata on the upper (adaxial) side of the leaf, than on the under (abaxial) side.[46] It has been theorised that this might be an effect of it having been domesticated and cultivated longer than any other plant.[47] Winter wheat generally produces up to 15 leaves per shoot and spring wheat up to 9[48] and winter crops may have up to 35 tillers (shoots) per plant (depending on cultivar).[48]

Wheat

fructans,[50] which helps the plant to yield under drought and disease pressure,[51] but it has been observed that there is a trade-off between root growth and stem non-structural carbohydrate reserves.[52]
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,[53] but wheat awns photosynthesise more efficiently than their leaves with regards to water usage,[54] 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.[55]

Genetics and breeding

Strains characterised

In traditional agricultural systems, wheat populations often consist 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.[56]

Major breeding objectives include high

Fusarium head blight (FHB), tan spot (Pyrenophora tritici-repentis), and stem rust (Puccinia graminis f. sp. tritici). In tropical areas, spot blotch
(also known as Helminthosporium leaf blight) is also important.

Wheat has also been the subject of

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.[57] Bread wheat with high grain iron and zinc content has been developed through gamma radiation breeding,[58] and through conventional selection breeding.[59]

International wheat breeding is led by the International Maize and Wheat Improvement Center in Mexico.

Syrian Civil War.[60]

Pathogens and this crop are constantly in a process of

adapted towards successful spore propagation, which is essentially to say its R0.[61] These pathogens tend towards high-R0 evolutionary attractors.[61]

Yields

Breeding has increased yields over time

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.[62] 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.[63] "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.[64] 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.[65]

T. turgidum subsp. polonicum is 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.[66][67]

As with many plants, MADS-box influences flower development, and more specifically, as with other agricultural Poaceae, heavily influences the total weight output at the end of the entire grain growing process. Despite that importance, as of 2021 little research has been done into MADS-box and other such spikelet and flower genetics in wheat specifically.[66]

The world record wheat yield is about 17 tonnes per hectare (15,000 pounds per acre), reached in New Zealand in 2017.[68] 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).[69][70]

Disease resistance

Different strains have been infected with the stem rust fungus. The strains bred to be resistant have their leaves unaffected or relatively unaffected by the fungus.

Wild grasses in the genus Triticum and related genera, and grasses such as

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.[73]

Marker-assisted breeding panels involving kompetitive allele specific PCR can be used. Singh et al. 2019 identify a KASP genetic marker for a pore-forming toxin-like gene providing FHB resistance.[78]

Hybrid wheats

Because wheat self-pollinates, creating hybrid seed is extremely labor-intensive; the high cost of hybrid wheat seed relative to its moderate benefits have kept farmers from adopting them widely[79][80] despite nearly 90 years of effort.[81]

F1 hybrid wheat cultivars should not be confused with wheat cultivars deriving from standard plant breeding, which may descend from hybrid crosses further back in its ancestry. 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 perfect in the botanical sense, meaning they have both male and female parts, and normally self-pollinate.[56] 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.[82]

Synthetic hexaploids made by crossing the wild goatgrass wheat ancestor Aegilops tauschii,[83] and various other Aegilops,[84] and various durum wheats are now being deployed, and these increase the genetic diversity of cultivated wheats.[85][86][87]

Triticale: Wheat-rye hybrid

The smaller grain of wheat on the left, larger kernels of rye in the middle, and triticale on the right – triticale grain is significantly larger than wheat
Wheat, rye, triticale

In ancient times, wheat was often considered a luxury grain because it had lower yield but better taste and digestibility than competitors like rye. In the 19th century, efforts were made to hybridize the two to get a crop with the best traits of both. This produced triticale, a grain with high potential, but fraught with problems relating to fertility and germination. These have mostly been solved, so that in the 20th century millions of acres of triticale are being grown worldwide.

Gluten

Modern bread wheat varieties have been

cross-bred to contain greater amounts of gluten,[88] which affords significant advantages for improving the quality of breads and pastas from a functional point of view.[89] 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."[90]

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 valuable carbon isotope based methods that are used for breeding wheat varieties with improved water-use efficiency. These varieties can improve crop productivity in rain-fed dry-land wheat farms.[91]

Insect resistance

The gene Sm1 protects against the

orange wheat blossom midge.[92][93][94][95]

Genome

In 2010, a team of UK scientists funded by BBSRC decoded the wheat genome (95% of the genome of a variety of wheat known as Chinese Spring line 42).[96] This genome was released in a basic format for scientists and plant breeders to use but was not fully annotated.[97] In 2012, an essentially complete gene set of bread wheat was published.[98] Random shotgun libraries of total DNA and cDNA from the T. aestivum cv. Chinese Spring (CS42) were sequenced in Roche 454 pyrosequencer using GS FLX Titanium and GS FLX+ platforms to generate 85 Gb of sequence (220 million reads) and identified between 94,000 and 96,000 genes.[98]In 2018 a more complete Chinese Spring genome was released by a different team.[99] In 2020 some of the same researchers produced 15 genome sequences from various locations and varieties around the world[93][94][95]r[93][94][95] – with examples of their own use of the sequences to localize particular insect and disease resistance factors.[93][94][95] The team expects these sequences will be useful in future cultivar breeding.[93][94][95] Wheat Blast Resistance is controlled by R genes which are highly race-specific.[100]

Genetic engineering

CRISPR/Cas9

For decades the primary

CRISPR/Cas9
tool has been extensively adopted, for example:

As of 2021[update] these examples illustrate the rapid deployment and results that CRISPR/Cas9 has shown in wheat disease resistance improvement.[101]

Naming

Further information: Taxonomy 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.

Hulled versus free-threshing species

Einkorn
. Note how the einkorn ear breaks down into intact spikelets.

The four wild species of wheat, along with the domesticated varieties

einkorn,[102] emmer[103] and spelt,[104] 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.[102] 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.[105]

Classes used in North America

Wheat classes are named by grain colour, season, and hardness.[106]The classes used in the United States are:[107][108]

As a food

Wheat is used in a wide variety of foods.
Wheat, hard red winter
Nutritional value per 100 g (3.5 oz)
Energy1,368 kJ (327 kcal)
71.18 g
Sugars0.41
Dietary fiber12.2 g
1.54 g
12.61 g
Niacin (B3)
34%
5.464 mg
Pantothenic acid (B5)
19%
0.954 mg
Vitamin B6
18%
0.3 mg
Folate (B9)
10%
38 μg
Choline
6%
31.2 mg
Vitamin E
7%
1.01 mg
Vitamin K
2%
1.9 μg
MineralsQuantity
%DV†
Calcium
2%
29 mg
Iron
18%
3.19 mg
Magnesium
30%
126 mg
Manganese
173%
3.985 mg
Phosphorus
23%
288 mg
Potassium
12%
363 mg
Sodium
0%
2 mg
Zinc
24%
2.65 mg
Other constituentsQuantity
Water13.1 g
Selenium70.7 µg
Link to USDA Database Entry
†Percentages estimated using US recommendations for adults,[111] except for potassium, which is estimated based on expert recommendation from the National Academies.[112]

Raw wheat can be ground into

groats.[113] If the raw wheat is broken into parts at the mill, as is usually done, the outer husk or bran
can be used in several ways.

Wheat is a major ingredient in such foods as

fermented beverage), and breakfast cereals.[114]

In manufacturing wheat products, gluten is valuable to impart

viscoelastic functional qualities in dough,[115] enabling the preparation of diverse processed foods such as breads, noodles, and pasta that facilitate wheat consumption.[116][11]

In 100 grams, wheat provides 1,368 kilojoules (327 kilocalories) of

dietary minerals are in significant content. Wheat is 13% water, 71% carbohydrates, and 1.5% fat. Its 13% protein content is mostly gluten (75–80% of the protein in wheat).[115]

Wheat proteins have a low quality for human nutrition, according to the new protein quality method (

white flours are more deficient in lysine compared with whole grains.[11] Significant efforts in plant breeding are being made to develop lysine-rich wheat varieties, without success as of 2017.[119] Supplementation with proteins from other food sources (mainly legumes) is commonly used to compensate for this deficiency,[14] since the limitation of a single essential amino acid causes the others to break down and become excreted, which is especially important during the period of growth.[11]

100 g (3+1⁄2 oz) of hard red winter wheat contain about 12.6 g of protein, 1.5 g of total fat, 71 g of carbohydrate (by difference), 12.2 g 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 g of protein, 1.9 g of total fat, 68 g of carbohydrate (by difference), 12.2 g of dietary fiber, and 3.6 mg of iron (20% of the daily requirement).[124]

Worldwide production

Wheat is grown on more than 218,000,000 hectares (540,000,000 acres).[125]

The most common forms of wheat are white and red wheat. However, other natural forms of wheat exist. Other commercially minor but nutritionally promising species of naturally evolved wheat species include black, yellow and blue wheat.[8][126][127]

Health effects

Cracked Wheat

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.[3][11] When eaten as the whole grain, wheat is a healthy food source of multiple nutrients and dietary fiber recommended for children and adults, in several daily servings containing a variety of foods that meet whole grain-rich criteria.[11][116][128][129] Dietary fiber may also help people feel full and therefore help with a healthy weight.[130] Further, wheat is a major source for natural and biofortified nutrient supplementation, including dietary fiber, protein and dietary minerals.[131]

Manufacturers of foods containing wheat as a whole grain in specified amounts are allowed a

soluble fiber, may reduce the risk of heart disease, a disease associated with many factors".[132][133] The scientific opinion of the European Food Safety Authority (EFSA) related to health claims on gut health/bowel function, weight control, blood glucose/insulin levels, weight management, blood cholesterol, satiety, glycaemic index, digestive function and cardiovascular health is "that the food constituent, whole grain, (...) is not sufficiently characterised in relation to the claimed health effects" and "that a cause and effect relationship cannot be established between the consumption of whole grain and the claimed effects considered in this opinion."[116][134]

Concerns

In genetically susceptible people, gluten – a major part of wheat protein – can trigger coeliac disease.[115][135] Coeliac disease affects about 1% of the general population in developed countries.[136][135] There is evidence that most cases remain undiagnosed and untreated.[135] The only known effective treatment is a strict lifelong gluten-free diet.[135]

While coeliac disease is caused by a reaction to wheat proteins, it is not the same as a

gluten ataxia, and dermatitis herpetiformis.[16]

It has been speculated that certain short-chain carbohydrates present in wheat, known as FODMAPs (and mainly frutose polymers), are the cause of non-coeliac gluten sensitivity. As of 2019, 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, such as neurological disorders, fibromyalgia, psychological disturbances, and dermatitis.[138][139][140]

Other proteins present in wheat called amylase-trypsin inhibitors (ATIs) have been identified as the possible activator of the

TLR4)-mediated intestinal inflammation in humans.[139][141][142] These TLR4-stimulating activities of ATIs are limited to gluten-containing cereals.[140] A 2017 study in mice demonstrated that ATIs exacerbate preexisting inflammation and might also worsen it at extraintestinal sites. This may explain why there is an increase of inflammation in people with preexisting diseases upon ingestion of ATIs-containing grains.[139]

Commercial use

A map of worldwide wheat production.

Harvested wheat grain that enters trade is classified according to grain properties for the purposes of the commodity- and international trade markets. Wheat buyers use these to decide which wheat to buy, as each class has special uses, and producers use them to decide which classes of wheat will be most profitable to cultivate.

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, for example, 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.

In recent years, low international wheat prices have often encouraged farmers in the United States to change to more profitable crops. In 1998, the price at harvest of a 60 pounds (27 kg) bushel[143] was $2.68 per.[144] Some information providers, following CBOT practice, quote the wheat market in per ton denomination.[145] A USDA report revealed that in 1998, average operating costs were $1.43 per bushel and total costs were $3.97 per bushel.[144] In that study, farm wheat yields averaged 41.7 bushels per acre (2.2435 metric ton/hectare), and typical total wheat production value was $31,900 per farm, with total farm production value (including other crops) of $173,681 per farm, plus $17,402 in government payments. There were significant profitability differences between low- and high-cost farms, due to crop yield differences, location, and farm size.

  • Annual agricultural production of wheat, measured in tonnes in 2014.[146]
    Annual agricultural production of wheat, measured in tonnes in 2014.[146]
  • Average wheat yields, measured in tonnes per hectare in 2014.[147]
    Average wheat yields, measured in tonnes per hectare in 2014.[147]

Production and consumption

Main article:
International wheat production statistics
Top wheat producers in 2020
Country Millions of tonnes
 China 134.2
 India 107.6
 Russia 85.9
 United States 49.7
 Canada 35.2
 France 30.1
 Pakistan 25.2
 Ukraine 24.9
 Germany 22.2
 Turkey 20.5
World 761
Source:
UN Food and Agriculture Organization[148]
Production of wheat (2019)[149]
Wheat prices in England, 1264–1996[150]

In 2020, world wheat production was 761 million tonnes, led by China, India, and Russia collectively providing 38% of the world total.[148] As of 2019, 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).[151]

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.[152] 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 the "Ridley's Stripper", to remove the heads of grain, and the reaper-harvester perfected by John Ridley in 1843.[153] By 1850 South Australia had become the granary for the region; soon wheat farming spread to Victoria and New South Wales, with heavy exports to Great Britain. In Canada modern farm implements made large scale wheat farming possible from the late 1840s on. By the 1879s 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.[154] 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.[155] 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.[156] 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.[157]

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.[158] 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.

In the 21st century, several factors are slowing the rate of global expansion of wheat production: population growth rates are falling while wheat yields continue to rise. There is evidence, however, that rising temperatures associated with

climate change are reducing wheat yield in several locations.[159]
In addition, the better economic profitability of other crops such as soybeans and maize, linked with investment in modern genetic technologies, has promoted shifts to other crops.

Farming systems

In 2014, the most productive crop yields for wheat were in Ireland, producing 10 tonnes per hectare.[9] 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. Various studies in India, for example, have concluded that about 10% of total wheat production is lost at farm level, another 10% is lost because of poor storage and road networks, and additional amounts lost at the retail level.[160]

In the

canola crop in the rotations has boosted wheat yields by a further 25%.[161] 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.[162]

Geographical variation

There are substantial differences in wheat farming, trading, policy, sector growth, and wheat uses in different regions of the world. The largest exporters of wheat in 2016 were, in order of exported quantities: Russian Federation (25.3 million tonnes), United States (24.0 million tonnes), Canada (19.7 million tonnes), France (18.3 million tonnes), and Australia (16.1 million tonnes).[163] The largest importers of wheat in 2016 were, in order of imported quantities: Indonesia (10.5 million tonnes), Egypt (8.7 million tonnes), Algeria (8.2 million tonnes), Italy (7.7 million tonnes) and Spain (7.0 million tonnes).[163]

In the rapidly developing countries of Asia and Africa, westernization of diets associated with increasing prosperity is leading to growth in per capita demand for wheat at the expense of the other food staples.[10]

The average annual world farm yield for wheat in 2014 was 3.3 tonnes per hectare (330 grams per square meter).[9] Ireland's wheat farms were the most productive in 2014, with a nationwide average of 10.0 tonnes per hectare, followed by the Netherlands (9.2), and Germany, New Zealand and the United Kingdom (each with 8.6).[9]

Peak wheat

This section is an excerpt from Peak wheat.[edit]
Food production per person increased since 1961.

Peak wheat is the concept that agricultural production, due to its high use of water and energy inputs,[164] is subject to the same profile as oil and other fossil fuel production.[165][166][167] The central tenet is that a point is reached, the "peak", beyond which agricultural production plateaus and does not grow any further,[168] and may even go into permanent decline.

Based on current

emerging economies, biofuels, declining acreage under irrigation, growing global population, stagnant agricultural productivity growth),[169] 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.[170][171][172]

According to the World Resources Institute, global per capita food production has been increasing substantially for the past several decades.[173]

Agronomy

Farming techniques

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.

  • Young crop
    Young crop
  • Month before harvest
    Month before harvest
  • Right before harvest
    Right before harvest
  • Field ready for harvesting
    Field ready for harvesting
  • Combine harvester threshes the wheat, crushes the chaff, then blows chaff across the field, and loads the threshed wheat onto a tractor trailer.
    Combine harvester threshes the wheat, crushes the chaff, then blows chaff across the field, and loads the threshed wheat onto a tractor trailer.

Crop development

Wheat normally needs between 110 and 130 days between sowing and harvest, depending upon climate, seed type, and soil conditions (

Zadoks scale). Knowledge of stages is also important to identify periods of higher risk from the climate. For example, 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.[174]
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 so should be preserved from disease or insect attacks to ensure a good yield.

Several systems exist to identify crop stages, with the

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.

Wheat at the anthesis stage. Face view (left) and side view (right) and wheat ear at the late milk

Pests and diseases

Pests[175] – or pests and diseases, depending on the definition – consume 21.47% of the world's wheat crop annually.[176]

Diseases

Main articles: Wheat diseases and List of wheat diseases
Rust-affected wheat seedlings

There are many wheat diseases, mainly caused by fungi, bacteria, and

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.[178] A wide range of organisms infect wheat, of which the most important are viruses and fungi.[179]

The main wheat-disease categories are:

Animal pests

Wheat is the food plant of the

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.[181] 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.[182] 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.[183]
Tracking insect infestations in stored grain is critical for food safety as well as for the marketing value of the crop.

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Further reading

  • The World Wheat Book : A History of Wheat Breeding

External links

Wikimedia Commons has media related to Wheat.
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