Wheat

• 1. Introduction

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  Wheat grows on more land than any other food crop on Earth. In 2024, farmers planted it across 219.5 million hectares, and the world harvested 799 million tonnes of grain. World trade in wheat is greater than that of all other crops combined. Yet this plant is simply a group of wild and domesticated grasses in the genus Triticum, raised for the small grains packed into each ripened ear.

  The archaeological record suggests wheat was first cultivated in the Fertile Crescent around 9600 BC. From those early fields, a single family of grasses spread to feed billions and to anchor the global food trade. How did a fragile wild grass become the leading source of vegetable protein in the human diet? How did hunter-gatherers turn a plant that scattered its own seeds into one that depends entirely on people to survive? And why does the protein that makes wheat so valuable also make a small share of those who eat it sick? The answers run from the steppes of Southwest Asia to the breeding labs of Mexico and the canvases of Vincent van Gogh.

• 2. The Body Of A Grass

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  At the top of a wheat stem sits a flower head holding some 20 to 100 flowers. Each flower contains both male and female parts, housed in a pair of small leaflike glumes. The flowers are wind-pollinated, and over 99 percent of pollination events are self-pollinations. The flowers cluster into spikelets, each carrying between two and six flowers. Every fertilised carpel develops into a grain, botanically a caryopsis fruit, which ripens to a golden yellow. A whole head of grain is called an ear.

  The stem itself is jointed and usually hollow, forming a straw, and one plant can carry many stems. Long narrow leaves sheathe the stem, one above each joint, emerging from the shoot apical meristem in a telescoping fashion until the plant turns to flowering. The final leaf, the flag leaf, is denser than the others and photosynthesises at a higher rate to feed the developing ear. In temperate countries, the flag leaf and the two leaves below it supply most of the carbohydrate in the grain, so their condition is critical for yield.

  Wheat roots reach as deep as 2 metres, among the deepest of any arable crop. As they grow, the plant stores energy in its stem as fructans, which helps it endure drought and disease. There is a trade-off here. Drought-adapted crops prioritise root growth, while varieties bred for disease-prone countries hold more carbohydrate reserves in the stem. Wheat is also unusual in carrying more stomata on the upper side of its leaf than the under side, a quirk some have theorised reflects its having been cultivated longer than any other plant.

  Some varieties grow awns, the bristles on the ear, and some do not. Producing awns costs grain number, but awns photosynthesise more efficiently than leaves when it comes to water use. For that reason they appear far more often in hot, drought-prone countries, and awned varieties could spread further as the climate warms.

• 3. Taming The Wild Grass

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  Hunter-gatherers in West Asia harvested wild wheats perhaps as early as 21,000 BC, long before anyone planted them on purpose, and at first they formed only a minor part of the diet. Repeated harvesting and sowing slowly favoured mutant forms, called sports, that suited cultivation. In domesticated wheat the grains are larger and stay attached to the ear by a toughened rachis during harvest. Wild strains have a fragile rachis that shatters easily and scatters the spikelets. Farmers may not have intended to select for non-shattering heads, but the trait made gathering seed easier, and that incidental selection drove domestication. The cost was severe. Highly domesticated wheat loses its natural seed dispersal and cannot survive in the wild.

  Wild einkorn wheat grows across Southwest Asia in open parkland and steppe, in three distinct races. Only one, native to Southeast Anatolia, was domesticated. People collected wild einkorn at sites such as Tell Abu Hureyra, dated around 10,700 to 9000 BC, and Mureybet, around 9800 to 9300 BC. The earliest evidence for the domestic form comes after about 8800 BC in southern Turkey, at Cayonu, Cafer Hoyuk, and possibly Nevali Cori. Genetic evidence shows it was domesticated in multiple places independently.

  Wild emmer wheat favoured the rocky basaltic and limestone soils of the Hilly Flanks of the Fertile Crescent. It was first cultivated in the southern Levant, as early as 9600 BC. Genetic studies show that, unlike einkorn, emmer was domesticated in southeastern Anatolia only once. The earliest secure evidence for domestic emmer comes from Cayonu, around 8300 to 7600 BC, where distinctive scars on the spikelets marked a hulled domestic variety. Emmer itself was born of a hybridisation in the wild between two diploid grasses, T. urartu and a wild goatgrass, long before any human took notice.

• 4. The First Harvests

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  Einkorn and emmer rank among the founder crops of the first farming societies in Neolithic West Asia. Those communities also grew naked wheats and a now-extinct domesticated form of Zanduri wheat, alongside many other crops. For the first thousand years of the Neolithic, barley predominated and wheat stayed relatively uncommon. After around 8500 BC it became a staple. Early cultivation took little labour. Farmers enclosed fields against grazing animals and re-sowed harvested stands, without systematically clearing vegetation or tilling the soil. Some exploited wetlands and floodplains for decrue farming, sowing into the mud left by receding floodwater. They reaped it with stone-bladed sickles.

  The ease of storing cereals slowly made households more reliant on them, especially once they built storage large enough to hold more than a year's supply. Grain was threshed, the chaff removed, and the rest ground into flour with stone mortars. A bread-like food made from ground einkorn and the tubers of the tuberous bulrush appeared as early as 12,400 BC. At Catalhoyuk, around 7100 to 6000 BC, people used both wholegrain wheat and flour to make bread, porridge, and gruel.

  Beyond food, wheat gave Neolithic societies straw. They used it for fuel, for wicker-making, and for wattle and daub construction. Domestic wheat then travelled fast to places its wild ancestors never grew. Emmer reached Cyprus as early as 8600 BC and Greece by 6500 BC, with einkorn following. Emmer reached Egypt shortly after 6000 BC, and both Germany and Spain by 5000 BC. Wheat arrived in the British Isles and Scandinavia by 4000 BC, in India around 3500 BC, and in China's lower Yellow River around 2600 BC.

• 5. A Tangle Of Genomes

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  Markings like the polyploidy levels assigned in a 2007 molecular phylogeny reveal a plant built from layered genomes. Some wheat species are diploid, carrying two sets of chromosomes, while many are stable polyploids with four sets or six. Einkorn is diploid, with two complements of seven chromosomes. Most tetraploid wheats, including emmer and durum, descend from wild emmer, which carries four complements of seven chromosomes in two groups.

  Hexaploid wheats arose later, and they arose in farmers' fields. Wild emmer hybridised with another goatgrass, Aegilops tauschii, to produce the hexaploid wheats including bread wheat. The origin of the D genome from Aegilops tauschii has been established through molecular analysis of many hexaploid varieties. The oldest evidence for hexaploid wheat comes from DNA analysis of seeds dated around 6400 to 6200 BC at Catalhoyuk. The earliest known wheat with enough gluten for yeasted breads is from a granary at Assiros in Macedonia, dated to 1350 BC.

  Ten thousand years of cultivation produced numerous forms, many of them hybrids, shaped by both artificial and natural selection. That complexity has caused much confusion in naming wheats. The wild species, along with domesticated einkorn, emmer, and spelt, have hulls, a more primitive morphology of toughened glumes that tightly enclose the grain. When threshed, hulled wheat breaks into spikelets, so milling or pounding is needed to free the grain. Free-threshing forms such as durum and common wheat have fragile glumes and a tough rachis, so threshing releases the grains directly. Hulled wheats are often stored as spikelets, because the toughened glumes guard well against pests of stored grain.

• 6. Food And Its Cost

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  Raw red winter wheat is 13 percent water, 71 percent carbohydrates including 12 percent dietary fibre, 13 percent protein, and 2 percent fat. Some 75 to 80 percent of that protein is gluten. In a 100 gram reference amount, wheat provides 1368 kilojoules of food energy and is a rich source of manganese, phosphorus, magnesium, zinc, and iron. The B vitamins niacin, thiamine, and vitamin B6 appear in significant amounts, niacin at 36 percent of the Daily Value.

  Globally, wheat is the leading source of vegetable proteins in human food, with a protein content of about 13 percent. That figure is relatively high for a cereal, but the quality is low. By the DIAAS protein quality method, wheat proteins are deficient in the essential amino acid lysine. Because gluten proteins in the endosperm are particularly poor in lysine, white flours fall shorter than whole grains. Plant breeders have tried to develop lysine-rich wheat without success, so supplementation with other foods, mainly legumes, compensates for the gap.

  Wheat berries can be ground into flour, or, using hard durum only, into semolina. They can be malted, cracked, or parboiled and de-branned into groats and then bulgur. Wheat is a major ingredient in bread, pasta, pastries, breakfast cereals, and drinks including beer, vodka, and the fermented beverage boza. In all of these, gluten supplies the viscoelastic qualities that hold a dough together.

  That same gluten carries a cost for a small share of people. In genetically susceptible individuals it can trigger coeliac disease, which affects about 1 percent of the general population in developed countries and has no known treatment but a strict lifelong gluten-free diet. Coeliac disease is not the same as a wheat allergy. Other conditions triggered by wheat include non-coeliac gluten sensitivity, estimated to affect 0.5 to 13 percent of people, along with gluten ataxia and dermatitis herpetiformis. Certain short-chain carbohydrates called FODMAPs may underlie some of this, while other wheat proteins, the amylase-trypsin inhibitors, appear to activate the innate immune system and may inflame the intestine.

• 7. The Yield Revolution

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  In 1869 it cost 37 cents to ship a bushel of wheat from Chicago to Liverpool. By 1905 it cost just 10 cents. That collapse in transport cost helped wheat become central to the British Empire in the 19th century. In Australia, with vast land and few workers, expansion leaned on technology. By the 1840s there were 900 growers in South Australia, using Ridley's Stripper, a reaper-harvester perfected by John Ridley in 1843. In Canada, modern implements made large-scale farming possible from the late 1840s, and by 1879 Saskatchewan was the center as railways carried grain to Britain. By 1910 wheat made up 22 percent of Canada's exports, rising to 25 percent in 1930 despite falling prices. After 1860, the expansion of United States production flooded the world market and lowered prices by 40 percent.

  Through the 20th century, global wheat output expanded about fivefold. Until about 1955 most of that came from planting more land, with only modest gains in yield per area. After 1955 the rate of yield improvement rose tenfold per year. Synthetic nitrogen fertiliser, irrigation, and wheat breeding drove the growth. Better seed storage helped too. In medieval England farmers saved a quarter of the harvest as seed for the next crop, but by 1999 the global average had fallen to about 6 percent of output.

  Norin 10 wheat, developed in Japan in the 1930s, carried dwarfing genes that proved transformative. Those genes divert carbon fixed in photosynthesis toward seed production and reduce lodging, when a tall stalk falls over in wind. They became major factors in the Green Revolution in Mexico and Asia, an initiative led by Norman Borlaug. By 1997-81 percent of the developing world's wheat area was planted to semi-dwarf wheats. The world record yield reached about 17 tonnes per hectare in New Zealand in 2017, while the UK record in 2018 stood at 16 tonnes per hectare and the average yield there was just 8.

• 8. An Embattled Crop

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  Pests and diseases consume 21.47 percent of the world's wheat crop annually. Most diseases come from fungi, bacteria, and viruses, and they fall into categories that read like a field manual. Seed-borne diseases include common bunt and loose smut. Leaf and head blights include powdery mildew, leaf rust, and Fusarium head scab. Crown and root rots include take-all and Cephalosporium stripe. Stem rust comes from Puccinia graminis, including the strain Ug99. A historically significant disease, ergot, is unusual in also sickening humans who eat grain contaminated with the fungus Claviceps purpurea.

  Breeders have answered with a steady search for resistance. Since the 1930s, wild grasses in Triticum and related genera, along with rye, have supplied disease-resistance traits. The wild relative Aegilops tauschii is the source of several genes effective against the Ug99 stem rust. The gene Lr67 is effective against all races of leaf, stripe, and stem rusts and powdery mildew, working by reducing glucose uptake through a mutation in a predicted hexose transporter. In 2003 the first resistance genes against fungal diseases in wheat were isolated, and in 2021 novel genes were identified against powdery mildew and wheat leaf rust.

  The genome itself slowed this work for decades. In 2010-95 percent of the genome of Chinese Spring line 42 was decoded, though not fully annotated. In 2012 an essentially complete gene set of bread wheat was published, identifying between 94,000 and 96,000 genes from 85 gigabases of sequence. In 2018 a more complete Chinese Spring genome appeared, and in 2020 fifteen genome sequences from varieties around the world were reported. The CRISPR tool has since been used to edit wheat extensively, including damaging genes to create novel male sterility traits and editing mildew resistance loci to build resistance to Blumeria graminis.

  The Dutch artist Vincent van Gogh painted his series Wheat Fields between 1885 and 1890, dozens of works made mostly across rural France. They show wheat crops in varied seasons and styles, sometimes green, sometimes at harvest, sometimes with farm workers among the stalks. Wheatfield with Crows was one of his last paintings, and is considered among his greatest works.

  In 1967, the American artist Thomas Hart Benton made his oil on wood painting Wheat, showing a row of uncut plants rising almost the full height of the canvas between rows of freshly cut stubble. The Smithsonian American Art Museum holds the work.

  In 1982, the American conceptual artist Agnes Denes grew a two-acre field of wheat at Battery Park in Manhattan. The ephemeral artwork has been described as an act of protest. After harvest, the wheat was divided and sent to 28 world cities for an exhibition titled The International Art Show for the End of World Hunger, carrying the grain that feeds billions back into a question about who goes without.