Wheat
Hunter-gatherers in West Asia harvested wild wheats for thousands of years before they were domesticated, perhaps as early as 21,000 BC. These early cultivars spread around the region and slowly developed traits that came to characterize their domesticated forms. Repeated harvesting and sowing of grains from wild grasses led to the creation of domestic strains. Mutant forms known as sports became more amenable to cultivation than their wild ancestors. In domesticated wheat, grains grew larger and seeds remained attached to the ear by a toughened rachis during harvesting. Wild strains featured a fragile rachis that allowed ears to shatter easily, dispersing spikelets naturally. Selection for larger grains and non-shattering heads occurred because these traits made gathering seeds easier for farmers. Such incidental selection was an important part of crop domestication. Highly domesticated strains cannot survive in the wild due to loss of natural seed dispersal mechanisms. Wild einkorn wheat grows across Southwest Asia in open parkland and steppe environments. It comprises three distinct races, only one native to Southeast Anatolia being domesticated. The main feature distinguishing domestic einkorn is that its ears do not shatter without pressure. This dependence on humans for dispersal and reproduction marked a fundamental shift in plant biology. Genetic evidence indicates domestication happened in multiple places independently. Wild emmer wheat favored rocky basaltic and limestone soils found in the Hilly Flanks of the Fertile Crescent. Domesticated varieties fell into two major groups: hulled or free-threshing. Free-threshing cultivars became more common over time. Wild emmer was first cultivated in the southern Levant as early as 9600 BC. Genetic studies confirm it was domesticated in southeastern Anatolia but only once. The earliest secure archaeological evidence for domestic emmer comes from Çayönü where distinctive scars on spikelets indicated they came from a hulled domestic variety.
Wheat is a stout grass of medium to tall height with jointed stems that are usually hollow forming straw. Many stems can grow on one plant alongside long narrow leaves whose bases sheath the stem at each joint. At the top of the stem sits the flower head containing some 20 to 100 flowers. Each flower contains both male and female parts allowing self-pollination which accounts for over 99% of pollination events. The remaining percentage represents cross-pollinations facilitated by wind movement. Flowers reside inside pairs of small leaflike glumes while stamens and stigmas protrude outside these protective coverings. Flower clusters group into spikelets each holding between two and six flowers. Fertilized carpels develop into wheat grains botanically classified as caryopsis fruits often called seeds. Grains ripen to golden yellow color before harvest when heads become known as ears. Leaves emerge from the shoot apical meristem in telescoping fashion until transition to flowering occurs. The last leaf produced by a wheat plant is known as the flag leaf. It possesses higher photosynthetic rates than other leaves supplying carbohydrate to developing ears. In temperate countries the flag leaf along with second and third highest leaves supply majority carbohydrates needed for grain formation. Wheat exhibits unusual stomata distribution with more pores on upper leaf sides compared to under surfaces. This trait may reflect effects of prolonged cultivation duration relative to other plants. Winter wheat generally produces up to 15 leaves per shoot while spring wheat reaches only nine. Winter crops can generate up to 35 tillers depending on specific cultivar characteristics. Roots extend as far down as three meters making them among deepest arable crop systems. During root growth phases plants accumulate energy stores within stems as fructans helping yield under drought conditions. Trade-offs exist between prioritizing root development versus stem non-structural carbohydrate reserves. Root growth likely takes precedence in drought-adapted varieties whereas stem reserves dominate disease-prone regions. Some varieties produce awns which incur costs regarding grain numbers but photosynthesize more efficiently regarding water usage. Awns appear frequently in hot drought-prone country varieties compared to those grown in temperate zones. Climate change could drive wider adoption of awned varieties given their efficiency advantages.
In 2023 world wheat production reached 799 million tonnes led by China India and Russia collectively providing 42.4% of total output. The largest exporters included Russia shipping 32 million tonnes followed by the United States at 27 million tonnes Canada delivering 23 million tonnes and France contributing 20 million tonnes. Major importers consisted of Indonesia taking 11 million tonnes Egypt purchasing 10.4 million tonnes and Turkey acquiring 10.0 million tonnes. Wheat cultivation covered vast areas globally exceeding any other food crop in 2021. World trade volumes surpassed all other crops combined demonstrating economic significance. Global demand continues increasing due to unique viscoelastic properties of gluten proteins facilitating processed food production. Industrialization processes worldwide have driven consumption patterns toward greater reliance on wheat products. Western dietary shifts further amplified this trend. In Australia technological advances enabled expanded production despite limited workforce availability. By the 1840s South Australia hosted 900 growers utilizing Ridley's Stripper reaper-harvester perfected by John Ridley in 1843. Canadian modern farm implements facilitated large-scale farming from late 1840s onward. Saskatchewan emerged as center by 1879 followed by Alberta Manitoba and Ontario as railway lines allowed easy exports to Britain. Wheat constituted 22% of Canadian exports by 1910 rising to 25% in 1930 despite sharp price declines during Great Depression. American wheat frontier moved rapidly westward during nineteenth century. By 1880s seventy percent of American exports went directly to British ports. First successful grain elevator construction occurred in Buffalo in 1842 reducing transport costs significantly. Transportation expenses dropped from thirty-seven cents per bushel shipping Chicago to Liverpool in 1869 down to ten cents by 1905. India became second largest producer globally by year 2000 after earlier struggles with low yields and disease outbreaks.
Raw red winter wheat contains thirteen percent water seventy-one percent carbohydrates including twelve percent dietary fiber plus thirteen percent protein and two percent fat composition. Some seventy-five to eighty percent of total protein content exists as gluten making it significant source vegetable proteins human food. Reference amounts provide substantial daily values for multiple minerals including manganese phosphorus magnesium zinc iron B vitamins niacin thiamine vitamin B6. Wheat supplies essential amino acids though lysine deficiency remains problematic especially within white flour varieties compared whole grains. Plant breeders attempted developing lysine-rich varieties without success so supplementation using legume proteins compensates deficiencies. Coeliac disease affects approximately one percent general population developed countries requiring strict lifelong gluten-free diets effective treatment option. Other conditions triggered include non-coeliac gluten sensitivity estimated affecting zero point five to thirteen percent general population gluten ataxia dermatitis herpetiformis. Certain short-chain carbohydrates called FODMAPs mainly fructose polymers may cause gastrointestinal symptoms like bloating explaining some but not extra-digestive manifestations. Amylase-trypsin inhibitors activate innate immune system triggering intestinal inflammation in susceptible individuals these proteins part plant natural defense mechanisms against insects. Consumed worldwide billions people wheat serves significant nutrition role particularly least developed countries where products primary foods. Whole grain consumption supplies multiple nutrients dietary fiber recommended children adults globally.
Wheat functions annual crop planted autumn harvested early summer winter climates or spring planted autumn harvested spring wheat variants. Farmers typically till soil ploughing harrowing killing weeds creating even surfaces before scattering seeds drilling rows. Winter wheat lies dormant during freeze requiring long period below four degrees Celsius suffering heat stress temperatures rise above thirty-two degrees Celsius. Spring wheat grows best between twenty-one and twenty-four degrees Celsius tolerating ranges four to thirty-five degrees Celsius germination below four reduces yields maturation above thirty-five limits production. Deep loam soils rich organic matter minerals nitrogen phosphorus potassium suit cultivation acid peaty unsuitable varieties require thirty-eight centimeters rain growing season forming good crops. Farmers intervene adding fertilizer irrigation pesticides herbicides insecticides assessing soil minerals water weed growth pest arrivals selecting harvest timing. Combine harvesters perform reaping cutting stems gathering crop threshing breaking ears releasing grains drying stored safely from mould fungi. Technological advances replaced broadcasting sowing seed drills increasing productivity nineteenth century. Crop rotations improved yields land long cultivated widespread fertilizer use enhanced plant growth. Automation progressed threshing machines large combine harvesters greatly increased productivity worldwide. Norman Borlaug developed dwarf wheat Green Revolution dramatically boosting yields Mexico Asia initiatives. By 1997 eighty-one percent developing world wheat area planted semi-dwarf wheats yielding increased responses nitrogenous fertilizers. World record yield reached approximately fifteen tonnes per hectare New Zealand 2017 UK Rothamsted Research aimed raising country yields ten tonnes by 2020 achieving eight point five average just under target goals. International Maize Wheat Improvement Center leads global breeding efforts ICARDA relocated Syria Lebanon Syrian Civil War impacting operations.
In 2010 ninety-five percent genome Chinese Spring line forty-two wheat decoded released basic format scientists breeders use fully annotated version. Two thousand twelve published essentially complete gene set bread wheat Random shotgun libraries total DNA cDNA T aestivum cv Chinese Spring CS42 sequenced generating eighty-five gigabases sequence two hundred million reads identifying between ninety-four thousand ninety-six thousand genes. Twenty-eighteen released more complete Chinese Spring genome different team twenty-twenty reported fifteen genome sequences various locations varieties worldwide examples localize particular insect disease resistance factors. R genes control highly race-specific traits identified through molecular analysis. Non-homologous end joining primary genetic modification technique decades CRISPR tool extensively used since introduction damaging three homologs TaNP1 glucose-methanol-choline oxidoreductase gene producing novel male sterility trait Li et al 2020. Shan Wang edited mildew resistance locus o genes producing Blumeria graminis f.sp tritici resistance Zhang knocked out EDR1 inhibiting Bmt resistance improving that protection Su disabled HRC producing Gibberella zeae resistance Okada knocked out Ms1 creating another novel male sterility Zhang subjected acetolactate synthase acetyl-CoA-carboxylase base changes conferring herbicide resistance ALS ACCase inhibitors respectively. Modified resistance genes tested transgenic wheat barley plants. Wild grasses genus Triticum related genera rye source many disease-resistance traits cultivated breeding since nineteen-thirties. Resistance genes identified Pyrenophora tritici-repentis races one five problematic Kazakhstan wild relative Aegilops tauschii source several genes effective against TTKSK/Ug99 Sr33 Sr45 Sr46 SrTA1662. Lr67 effective all races leaf stripe stem rusts powdery mildew produced mutation two amino acids hexose transporter reducing glucose uptake widely deployed cultivars worldwide. Powdery mildew resistance introgressed rye Secale cereale comes rye chromosome one R source many resistances since nineteen-sixties. Marker-assisted breeding panels involving kompetitive allele specific PCR used Fusarium ear blight FHB important target pore-forming toxin-like gene provides FHB resistance KASP genetic marker. First resistance genes fungal diseases isolated 2003 novel resistance genes identified 2021 powdery mildew wheat leaf rust.
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Common questions
When was wheat first domesticated by hunter-gatherers in West Asia?
Hunter-gatherers in West Asia harvested wild wheats for thousands of years before they were domesticated, perhaps as early as 21000 BC. These early cultivars spread around the region and slowly developed traits that came to characterize their domesticated forms.
What are the main differences between wild einkorn wheat and domesticated einkorn wheat?
Wild einkorn wheat grows across Southwest Asia in open parkland and steppe environments with a fragile rachis that allows ears to shatter easily. Domesticated varieties feature a toughened rachis where grains remain attached to the ear during harvesting without shattering without pressure.
Which countries produced the most wheat globally in 2023?
In 2023 world wheat production reached 799 million tonnes led by China India and Russia collectively providing 42.4% of total output. The largest exporters included Russia shipping 32 million tonnes followed by the United States at 27 million tonnes Canada delivering 23 million tonnes and France contributing 20 million tonnes.
How does winter wheat differ from spring wheat regarding temperature tolerance and growth cycles?
Winter wheat lies dormant during freeze requiring long period below four degrees Celsius suffering heat stress temperatures rise above thirty-two degrees Celsius. Spring wheat grows best between twenty-one and twenty-four degrees Celsius tolerating ranges four to thirty-five degrees Celsius germination below four reduces yields maturation above thirty-five limits production.
What genetic modifications have scientists applied to wheat since 2010?
In 2010 ninety-five percent genome Chinese Spring line forty-two wheat decoded released basic format scientists breeders use fully annotated version. Two thousand twelve published essentially complete gene set bread wheat Random shotgun libraries total DNA cDNA T aestivum cv Chinese Spring CS42 sequenced generating eighty-five gigabases sequence two hundred million reads identifying between ninety-four thousand ninety-six thousand genes.