Wheat

Wheat (Triticum spp.) is a grass, originally from the Fertile Crescent region of the Near East, but now cultivated worldwide. In 2007 world production of wheat was 607 million tons, making it the third most-produced cereal after maize (784 million tons) and rice (651 million tons). Globally, wheat is the leading source of vegetable protein in human food, having a higher protein content than either maize (corn) or rice, the other major cereals. In terms of total production tonnages used for food, it is currently second to rice as the main human food crop, and ahead of maize, after allowing for maize's more extensive use in animal feeds.

Wheat was a key factor enabling the emergence of city-based societies at the start of civilization because it was one of the first crops that could be easily cultivated on a large scale, and had the additional advantage of yielding a harvest that provides long-term storage of food. Wheat is a factor in contributing to city-states in the Fertile Crescent including the Babylonian and Assyrian empires. Wheat grain is a staple food used to make flour for leavened, flat and steamed breads, biscuits, cookies, cakes, breakfast cereal, pasta, noodles, couscous and for fermentation to make beer, other alcoholic beverages, or biofuel.

Wheat is planted to a limited extent as a forage crop for livestock, and its straw can be used as a construction material for roofing thatch. The whole grain can be milled to leave just the endosperm for white flour. The products of this are bran and germ. The whole grain is a concentrated source of vitamins, minerals, and protein, while the refined grain is mostly starch.

History

Wheat is one of the first cereals known to have been domesticated, and wheat's ability to self-pollinate greatly facilitated the selection of many distinct domesticated varieties. The archaeological record suggests that this first occurred in the regions known as the Fertile Crescent, and the Nile Delta. These include southeastern parts of Turkey, Syria, the Levant, Israel, and Egypt. Recent findings narrow the first domestication of wheat down to a small region of southeastern Turkey, and domesticated Einkorn wheat at Nevalı Çori— northwest of Gobekli Tepe in Turkey—has been dated to 9,000 B.C. However evidence for the exploitation of wild barley has been dated to 23,000 B.C. and some say this is also true of pre-domesticated wheat.

Origin

Genetic analysis of wild einkorn wheat suggests that it was first grown in the Karacadag Mountains in southeastern Turkey. Dated archeological remains of einkorn wheat in settlement sites near this region, including those at Abu Hureyra in Syria, confirms the domestication of einkorn near the Karacadag Mountain Range. The earliest carbon-14 date for the einkorn wheat remains at Abu Hureyra is 7800 to 7500 years BCE. Recent genetic and archeological discoveries indicate that both emmer wheat and durum (hard pasta wheat) also originated from this same Karacadag region of southeastern Turkey. Remains of harvested emmer from several sites near the Karacadag Range have been dated to between 8800 and 8400 BCE, that is, in the Neolithic period.

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 (spikelets) remain attached to the ear by a toughened rachis during harvesting. In wild strains, a more fragile rachis allows the ear to easily shatter and disperse the spikelets. Selection for these traits 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.

Cultivation of wheat began to spread beyond the Fertile Crescent after about 8000 BCE. Jared Diamond traces the spread of cultivated emmer wheat starting in the Fertile Crescent about 8500 BCE, reaching Greece, Cyprus and India by 6500 BCE, Egypt shortly after 6000 BCE, and Germany and Spain by 5000 BCE. "The early Egyptians were developers of bread and the use of the oven and developed baking into one of the first large-scale food production industries." By 3000 BCE, wheat had reached England, and Scandinavia. A millennium later it reached China.

Wheat spread through out Europe and in England; thatch was used for roofing in the Bronze Age, and was in common use until the late 19th century.

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. Agricultural cultivation using horse collar leveraged plows (at about 3000 BCE) was one of the first innovations that increased productivity. Much later, when the use of seed drills replaced broadcasting sowing of seed in the 18th century, another great increase in productivity occurred. Yields of 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 and reaping machines (the 'combine harvester'), tractor-drawn cultivators and planters, and better varieties (see Green Revolution and Norin 10 wheat). Great expansions of wheat production occurred as new arable land was farmed in the Americas and Australia in the 19th and 20th centuries.

Genetics

Wheat genetics is more complicated than that of most other domesticated species. Some wheat species are diploid, with two sets of chromosomes, but many are stable polyploids, with four sets of chromosomes (tetraploid) or six (hexaploid). Einkorn wheat (T. monococcum) is diploid (AA, two complements of seven chromosomes, 2n=14).

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 complete and normally self-pollinate. Commercial hybrid wheat seed has been produced using chemical hybridizing agents; these chemicals 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 USA and South Africa. F1 hybrid wheat cultivars should not be confused with the standard method of breeding inbred wheat cultivars by crossing two lines using hand emasculation, then selfing or inbreeding the progeny many (ten or more) generations before release selections are identified to be released as a variety or cultivar.

Synthetic hexaploids made by crossing the wild goatgrass wheat ancestor Aegilops tauschii and various durum wheats are now being deployed, and these increase the genetic diversity of cultivated wheats.

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.

In 2010, a team of UK scientists funded by BBSRC announced they had decoded the wheat genome for the first time (95% of the genome of a variety of wheat known as Chinese Spring line 42). This was the expressed genome and was released in a basic format for scientists and plant breeders to use but was not a fully annotated sequence which was reported in some of the media. A fully annotated sequence is being assembled by a global consortium (IWGSC http://www.wheatgenome.org/), including members of this team.

Plant breeding

In traditional agricultural systems wheat populations often consist of landraces, informal farmer-maintained populations that often maintain high levels of morphological diversity. Although landraces of wheat are no longer 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. 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.

The major breeding objectives include high grain yield, good quality, disease and insect resistance and tolerance to abiotic stresses include mineral, moisture and heat tolerance. The major diseases in temperate environments include the following, arranged in a rough order of their significance from cooler to warmer climates: eyespot, Stagonospora nodorum blotch (also known as glume blotch), yellow or stripe rust, powdery mildew, Septoria tritici blotch (sometimes known as leaf blotch), brown or leaf rust, Fusarium head blight, tan spot and stem rust. In tropical areas, spot blotch (also known as Helminthosporium leaf blight) is also important.

Hulled versus free-threshing wheat

The four wild species of wheat, along with the domesticated varieties einkorn, emmer and spelt, 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. In contrast, 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. Hulled wheats are often stored as spikelets because the toughened glumes give good protection against pests of stored grain.

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 by the Chicago Board of Trade.

Hard White – Hard, light-colored, opaque, chalky, medium-protein wheat planted in dry, temperate areas. Used for bread and brewing.

Soft White – Soft, light-colored, very low protein wheat grown in temperate moist areas. Used for pie crusts and pastry. Pastry flour, for example, is sometimes made from soft white winter wheat.

Red wheats may need bleaching; therefore, white wheats usually command higher prices than red wheats on the commodities market.

As a food

Raw wheat can be ground into flour or - using hard durum wheat only, can be ground into semolina; germinated and dried creating malt; crushed or cut into cracked wheat; parboiled (or steamed), dried, crushed and de-branned into bulgur also known as groats. If the raw wheat is broken into parts at the mill, as is usually done, the outer husk or bran can be used several ways. Wheat is a major ingredient in such foods as bread, porridge, crackers, biscuits, Muesli, pancakes, pies, pastries, cakes, cookies, muffins, rolls, doughnuts, gravy, boza (a fermented beverage), and breakfast cereals (e.g., Wheatena, Cream of Wheat, Shredded Wheat, and Wheaties).

Nutrition

100 grams of hard red winter wheat contain about 12.6 grams of protein, 1.5 grams of total fat, 71 grams of carbohydrate (by difference), 12.2 grams 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 grams of protein, 1.9 grams of total fat, 68 grams of carbohydrate (by difference), 12.2 grams of dietary fiber, and 3.6 mg of iron (20% of the daily requirement).

Much of the carbohydrate fraction of wheat is starch. Wheat starch is an important commercial product of wheat, but second in economic value to wheat gluten. The principal parts of wheat flour are gluten and starch. These can be separated in a kind of home experiment, by mixing flour and water to form a small ball of dough, and kneading it gently while rinsing it in a bowl of water. The starch falls out of the dough and sinks to the bottom of the bowl, leaving behind a ball of gluten.

Health concerns

Roughly 1% of Indian populations has coeliac (also written as celiac) disease—a condition that is caused by an adverse immune system reaction to gliadin, a gluten protein found in wheat (and similar proteins of the tribe Triticeae which includes other species such as barley and rye). Upon exposure to gliadin, the enzyme tissue transglutaminase modifies the protein, and the immune system cross-reacts with the bowel tissue, causing an inflammatory reaction. That leads to flattening of the lining of the small intestine, which interferes with the absorption of nutrients. The only effective treatment is a lifelong gluten-free diet.

The estimate for people in the United States is between 0.5 and 1.0 percent of the population.

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

Synopsis of major staple food

Commercial use

Harvested wheat grain that enters trade is classified according to grain properties for the purposes of the commodities market. 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 like 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 USA to change to more profitable crops. In 1998, the price at harvest was $2.68 per bushel. A USDA report revealed that in 1998, average operating costs were $1.43 per bushel and total costs were $3.97 per bushel. 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, mainly due to crop yield differences, location, and farm size.

In 2007 there was a dramatic rise in the price of wheat due to freezes and flooding in the northern hemisphere and a drought in Australia. Wheat futures in September, 2007 for December and March delivery had risen above $9.00 a bushel, prices never seen before. There were complaints in Italy about the high price of pasta. This followed a wider trend of escalating food prices around the globe, driven in part by climatic conditions such as drought in Australia, the diversion of arable land to other uses (such as producing government-subsidised bio-oil crops), and later by some food-producing nations placing bans or restrictions on exports in order to satisfy their own consumers.

Other drivers affecting wheat prices include the movement to bio fuels (in 2008, a third of corn crops in the US are expected to be devoted to ethanol production) and rising incomes in developing countries, which is causing a shift in eating patterns from predominantly rice to more meat based diets (a rise in meat production equals a rise in grain consumption—seven kilograms of grain is required to produce one kilogram of beef).

Production and consumption

In 2003, global per capita wheat consumption was 67 kg, with the highest per capita consumption (239 kg) found in Kyrgyzstan. In 1997, global wheat consumption was 101 kg per capita, with the highest consumption (623 kg per capita) in Denmark, but most of this (81%) was for animal feed. Wheat is the primary food staple in North Africa and the Middle East, and is growing in popularity in Asia. Unlike rice, wheat production is more widespread globally though China's share is almost one-sixth of the world.

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 dramatic 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.

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.

Several factors are currently slowing the rate of global expansion of wheat production: population growth rates are falling while wheat yields continue to rise, and 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 the Punjab region of India and Pakistan, 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. 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 'rotation cropping' (traditionally called the ley system) with leguminous pastures and, in the last decade, including a canola crop in the rotations has boosted wheat yields by a further 25% . 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.

Futures contracts

Wheat futures are traded on the Chicago Board of Trade, Kansas City Board of Trade, and Minneapolis Grain Exchange, and have delivery dates in March (H), May (K), July (N), September (U), and December (Z).

Geographical variation

There are substantial differences in wheat farming, trading, policy, sector growth, and wheat uses in different regions of the world. In the EU and Canada for instance, there is significant addition of wheat to animal feeds, but less so in the USA.

The two biggest wheat producers are China and the EU, followed currently by India, then USA. Developed countries USA, Canada, Australia, the EU and increasingly Argentina are the major exporters with developing countries being the main importers, although both India and China are close to being self-sufficient in wheat. In the rapidly developing countries of Asia, 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.

In the past, there has been significant governmental intervention in wheat markets, such as price supports in the USA and farm payments in the EU. In the EU these subsidies have encouraged heavy use of fertilizers inputs with resulting high crop yields. In Australia and Argentina direct government subsidies are much lower.

Agronomy

Crop development

Wheat normally needs between 110 and 130 days between planting and harvest, depending upon climate, seed type, and soil conditions (winter wheat lies dormant during a winter freeze). 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, 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. 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. 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 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.

Diseases

There are many wheat diseases, mainly caused by fungi, bacteria, and viruses. 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 10–25% in Missouri. A wide range of organisms infect wheat, of which the most important are viruses and fungi.

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.

Leaf- and head- blight diseases: Powdery mildew, leaf rust, Septoria tritici leaf blotch, Stagonospora (Septoria) nodorum leaf and glume blotch, and Fusarium head scab.

Crown and root rot diseases: Two of the more important of these are 'take-all' and Cephalosporium stripe. Both of these diseases are soil borne.

Viral diseases: Wheat spindle streak mosaic (yellow mosaic) and barley yellow dwarf are the two most common viral diseases. Control can be achieved by using resistant varieties.

Pests

Wheat is used as a food plant by 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, birds and rodents can also 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 USA alone, and damage to wheat by various borers, beetles and weevils is no exception. 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. 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 300,000 good ones. Tracking insect infestations in stored grain is critical for food safety as well as for the marketing value of the crop.

See also

Bran

Chaff

Deficit irrigation

History of agriculture in the United States#Wheat

Husk

Wheat germ oil

Wheat middlings

Whole wheat flour

References

Further reading

Bonjean, A.P., and W.J. Angus (editors). The World Wheat Book: a history of wheat breeding. Lavoisier Publ., Paris. 1131 pp. (2001). ISBN 2-7430-0402-9

| Verlag = DLG-Verlags-GmbH | Jahr = 2009 | ISBN = 978-3-7690-0719-0}}

Garnsey Peter, Grain for Rome, in Garnsey P., Hopkins K., Whittaker C. R. (editors), Trade in the Ancient Economy, Chatto & Windus, London 1983

Jasny Naum, The daily bread of ancient Greeks and Romans, Ex Officina Templi, Brugis 1950

Jasny Naum, The Wheats of Classical Antiquity, J. Hopkins Press, Baltimore 1944

Heiser Charles B., Seed to civilisation. The story of food, Harvard University Press, Harvard Mass. 1990

Harlan Jack R., Crops and man, American Society of Agronomy, Madison 1975

Saltini Antonio, I semi della civiltà. Grano, riso e mais nella storia delle società umane, Prefazione di Luigi Bernabò Brea, Avenue Media, Bologna 1996

Sauer Jonathan D., Geography of Crop Plants. A Select Roster, CRC Press, Boca Raton

External links

Information on wheat genome sequencing

Crop Wild Relatives Gap Analysis Portal reliable information source on where and what to conserve ex-situ, regarding Triticum genepool

Price history of wheat, according to the IMF

Photos of wheat fields

Watch Australian science documentary on developing drought-resistant wheat

Wheat Foods Council Est. 1972

NAWG—Web site of the National Association of Wheat Growers

CIMMYT—Web site of the International Maize and Wheat Improvement Center

Triticum species at Purdue University

A Workshop Report on Wheat Genome Sequencing

Molecular Genetic Maps in Wild Emmer Wheat

Winter Wheat in the Golden Belt of Kansas by James C. Malin, University of Kansas, 1944

Varieties of club wheat hosted by the UNT Government Documents Department

Triticum aestivum: facts, developmental stages, and inflorescence at GeoChemBio

Major topic "Triticum": free full-text articles in National Library of Medicine

"Gold Harvest Feeds The World" Popular Mechanics, July 1949, post World War Two modernization of wheat harvesting

Category:Crops Category:Energy crops Category:Poaceae genera Category:Staple foods