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Maize

2007 Schools Wikipedia Selection. Related subjects: Plants

                    iMaize
   Cultivars of maize
   Cultivars of maize
           Scientific classification

   Kingdom:  Plantae
   Division: Magnoliophyta
   Class:    Liliopsida
   Order:    Poales
   Family:   Poaceae
   Genus:    Zea
   Species:  Z. mays

                                Binomial name

   Zea mays
   L.

   Maize (Zea mays ssp. mays), also known as corn, is a cereal grain that
   was domesticated in Mesoamerica and then spread throughout the American
   continents. It spread to the rest of the world after European contact
   with the Americas in the late 15th century and early 16th century. The
   term maíze derives from the Spanish form of the Arawak Indian term for
   the plant. However, it is popularly called corn in the United States,
   English Canada (in French Canada it is called maïs), New Zealand, and
   Australia. Corn is a shortened form of "Indian corn", i.e. the Indian
   grain. The English word "corn" originally referred to a granular
   particle, most commonly cereal grains. It is called mealies in southern
   Africa. Hybrid maize is favored by farmers over conventional varieties
   for its high grain yield, due to heterosis ("hybrid vigor"). Maize is
   one of the first crops for which genetically modified varieties make up
   a significant proportion of the total harvest.

   While some maize varieties grow 7 m (23 ft) tall at certain locations
   [Kuleshov 1933], commercial maize has been bred for a height of 2.5 m
   (8 ft). Sweetcorn is usually shorter than field-corn varieties.

Corn physiology

   The stems superficially resemble bamboo canes and the joints ( nodes)
   are about 20–30 cm (8–12 in) apart. Maize has a very distinct growth
   form, the lower leaves being like broad flags, 50–100 cm long and 5–10
   cm wide (2–4 ft by 2–4 in); the stems are erect, conventionally 2–3 m
   (7–10 ft) in height, with many nodes, casting off flag-leaves at every
   node. Under these leaves and close to the stem grow the ears. They grow
   about 3 cm a day.
   Corn plants showing ears
   Enlarge
   Corn plants showing ears

   The ears are female inflorescences, tightly covered over by several
   layers of leaves, and so closed-in by them to the stem that they do not
   show themselves easily until the emergence of the pale yellow silks
   from the leaf whorl at the end of the ear. The silks are elongated
   stigmas that look like tufts of hair, at first green, and later red or
   yellow. Maize planted individually develops 2 to 4 ears. Modern farming
   techniques in developed countries usually rely on dense planting, which
   produces on average only about 0.9 ears per stalk because it stresses
   the plants. Plantings for silage are even denser, and achieve an even
   lower percentage of ears and more plant matter. Certain varieties of
   maize have been bred to produce many additional developed ears, and
   these are the source of the "baby corn" that is used as a vegetable in
   Asian cuisine.

   Maize cultivars grown in the temperate zone are considered day-neutral
   and flower after a certain number of days at > 50° F (10°C). However,
   maize cultivars from tropical locations typically have a short-day
   requirement for flowering and generally do not produce seed in the long
   summer days at higher latitudes. The day-length requirement for
   flowering is controlled genetically and regulated by the phytochrome
   system.

   The apex of the stem ends in the tassel, an inflorescence of male
   flowers. Each silk may become pollinated to produce one kernel of corn.
   Young ears can be consumed raw, with the cob and silk, but as the plant
   matures (usually during the summer months) the cob becomes tougher and
   the silk dries to inedibility. By late August the kernels have dried
   out and become difficult to chew without cooking them tender first in
   boiling water.

   The kernel of corn has a pericarp of the fruit fused with the seed
   coat, typical of the grasses. It is close to a multiple fruit in
   structure, except that the individual fruits (the kernels) never fuse
   into a single mass. The grains are about the size of peas, and adhere
   in regular rows round a white pithy substance, which forms the ear. An
   ear contains from two to four hundred grains, and is from 10–25 cm
   (4–10 in) in length. They are of various colors: blackish, bluish-gray,
   red, white and yellow. When ground into flour, maize yields more flour,
   with much less bran, than wheat does. However, it lacks the protein
   gluten of wheat and therefore makes baked goods with poor rising
   capability.

   A genetic variation that accumulates more sugar and less starch in the
   ear is consumed as a vegetable and is called sweetcorn.

   Immature maize shoots accumulate a powerful antibiotic substance,
   DIMBOA (2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one). DIMBOA is a
   member of a group of hydroxamic acids (also known as benzoxazinoids)
   that serve as a natural defense against a wide range of pests including
   insects, pathogenic fungi and bacteria. DIMBOA is also found in related
   grasses, particularly wheat. A maize mutant (bx) lacking DIMBOA is
   highly susceptible to attack by aphids and fungi. DIMBOA is also
   responsible for the relative resistance of immature maize to the
   European corn borer (family Crambidae). As maize matures, DIMBOA levels
   and resistance to the corn borer decline.

Genetics

   Many forms of maize are used for food, once classified as various
   subspecies:
     * Flour corn - Zea mays L. subsp. mays Amylacea Group
     * Popcorn - Zea mays L. subsp. mays Everta Group
     * Dent corn - Zea mays L. subsp. mays Indentata Group
     * Flint corn - Zea mays L. subsp. mays Indurata Group
     * Sweetcorn - Zea mays L. subsp. mays Saccharata Group
     * Waxy corn - Zea mays L. ceratina Kuleshov
     * Amylomaize - Zea mays
     * Pod corn - Zea mays L. var. tunicata Larrañaga ex A. St. Hil.

   This system has been replaced over the last 60 years by multi-variable
   classifications based on ever more data. Agronomic data was
   supplemented by botanical traits for a robust initial classification,
   then genetic, cytological, protein and DNA evidence was added. Now the
   categories are forms (little used), races, racial complexes, and
   recently branches.

   Maize has 10 chromosomes (n=10). The combined length of the chromosomes
   is 1500 cM. Some of the maize chromosomes have what are known as
   "chromosomal knobs". They are highly repetitive heterochromatic domains
   that stain darkly. Individual knobs are polymorphic among strains of
   both maize and teosinte. Barbara McClintock used these knob markers to
   prove her transposon theory of "jumping genes".

   There is a stock centre of maize mutants, The Maize Genetics
   Cooperation - Stock Centre, funded by the USDA Agricultural Research
   Service and located in the Department of Crop Sciences at the
   University of Illinois at Urbana-Champaign. The total collection has
   nearly 80,000 samples. The bulk of the collection consists of several
   hundred named genes, plus additional gene combinations and other
   heritable variants. There are about 1000 chromosomal aberrations (e.g.,
   translocations and inversions) and stocks with abnormal chromosome
   numbers (e.g., tetraploids). Genetic data describing the maize mutant
   stocks as well as myriad other data about maize genetics can be
   accessed at MaizeGDB, the Maize Genetics and Genomics Database.

   In 2005, the U.S. National Science Foundation (NSF), Department of
   Agriculture ( USDA) and the Department of Energy (DOE) formed a
   consortium to sequence the maize genome. The resulting DNA sequence
   data will be deposited immediately into GenBank, a public repository
   for genome-sequence data. Sequencing the corn genome has been
   considered difficult because of its large size and complex genetic
   arrangements. The genome has 50,000–60,000 genes scattered among the
   2.5 billion bases – molecules that form DNA – that make up its 10
   chromosomes. (By comparison, the human genome contains about 2.9
   billion bases and 26,000 genes.)

Origin

   Two teosintes said to be the parents of maize
   Enlarge
   Two teosintes said to be the parents of maize

   There are several theories about the specific origin of maize in
   Mesoamerica:
    1. It is a direct domestication of a Mexican annual teosinte, Zea mays
       ssp. parviglumis, native to the Balsas River valley of southern
       Mexico, with up to 12% of its genetic material obtained from Zea
       mays ssp. mexicana through introgression;
    2. It derives from hybridization between a small domesticated maize (a
       slightly changed form of a wild maize) and a teosinte of section
       Luxuriantes, either Z. luxurians or Z. diploperennis;
    3. It underwent two or more domestications either of a wild maize or
       of a teosinte;
    4. It evolved from a hybridization of Z. diploperennis by Tripsacum
       dactyloides. (The term "teosinte" describes all species and
       subspecies in the genus Zea, excluding Zea mays ssp. mays.) In the
       late 1930s, Paul Mangelsdorf suggested that domesticated maize was
       the result of a hybridization event between an unknown wild maize
       and a species of Tripsacum, a related genus. However, the proposed
       role of tripsacum (gama grass) in the origins of maize has been
       refuted by modern genetic analysis, negating Mangelsdorf’s model
       and the fourth listed above.

   The third model (actually a group of hypotheses) is unsupported. The
   second parsimoniously explains many conundrums but is dauntingly
   complex. The first model was proposed by Nobel Prize winner George
   Beadle in 1939, and it has experimental support, but it has not
   explained a number of problems, among them:
    1. how the immense diversity of the species of sect. Zea originated,
    2. how the tiny archaeological specimens of 3500–2700 BC (uncorrected)
       could have been selected from a teosinte, and
    3. how domestication could have proceeded without leaving remains of
       teosinte or maize with teosintoid traits until ca. 1100 BC.

   Guila Naquitz Cave, site of the oldest known remains of maize
   Enlarge
   Guila Naquitz Cave, site of the oldest known remains of maize

   The domestication of maize is of particular interest to researchers—
   archaeologists, geneticists, ethnobotanists, geographers, etc. The
   process is thought by some to have started 7,500 to 12,000 years ago
   (corrected for solar variations). Recent genetic evidence suggests that
   maize domestication occurred 9000 years ago in central Mexico, perhaps
   in the highlands between Oaxaca and Jalisco. The wild teosinte most
   similar to modern maize grows in the area of the Balsas River.
   Archaeological remains of early maize cobs, found at Guila Naquitz Cave
   in the Oaxaca Valley, date back roughly 6,250 years (corrected; 3450
   BC, uncorrected); the oldest cobs from caves near Tehuacan, Puebla,
   date ca. 2750 BC. Little change occurred in cob form until ca. 1100 BC
   when great changes appeared in cobs from Mexican caves: maize diversity
   rapidly increased and archaeological teosinte was first deposited.

   Perhaps as early as 1500 BC, maize began to spread widely and rapidly.
   As it was introduced to new cultures, new uses were developed and new
   varieties selected to better serve in those preparations. Maize was the
   staple food, or a major staple, of most the pre-Columbian North
   American, Mesoamerican, South American, and Caribbean cultures. During
   the 1st millennium CE (AD), maize cultivation spread from Mexico into
   the U.S. Southwest and a millennium later into northeastern U.S. and
   southeast Canada, transforming the landscape as Native Americans
   cleared large forest and grassland areas for the new crop. Gavin
   Menzies, in his book 1421 - The Year China Discovered the World, claims
   to show that Maize was most likely transplanted from the Americas by
   the Chinese during their great voyages of the 15th century (although
   this claim is widely disputed ).

   It is unknown what precipitated its domestication, because the edible
   portion of the wild variety is too small and hard to obtain to be eaten
   directly, as each kernel is enclosed in a very hard bi-valve shell.
   However, George Beadle demonstrated that the kernels of teosinte are
   readily "popped" for human consumption, like modern popcorn. Some have
   argued that it would have taken too many generations of selective
   breeding in order to produce large compressed ears for efficient
   cultivation. However, studies of the hybrids readily made by
   intercrossing teosinte and modern maize suggest that this objection is
   not well-founded.

   In 2005, research by the USDA Forest Service indicated that the rise in
   maize cultivation 500 to 1,000 years ago in the southeastern United
   States contributed to the decline of freshwater mussels, which are very
   sensitive to environmental changes.

Cultivation

   Top Maize Producers
   in 2005
   (million metric tons)
   Flag of United States  United States      280
   Flag of People's Republic of China  China 131
   Flag of Brazil  Brazil                    35
   Flag of Mexico  Mexico                    21
   Flag of Argentina  Argentina              20
   Flag of Indonesia  Indonesia              15
   Flag of France  France                    13
   Flag of India  India                      12
   Flag of South Africa  South Africa        12
   Flag of Italy  Italy                      11
   World Total                               692
   Source:
   UN Food & Agriculture Organisation
   (FAO)

   Maize is widely cultivated throughout the world, and a greater weight
   of maize is produced each year than any other grain. While the United
   States produces almost half of the world's harvest, other top producing
   countries are as widespread as China, Brazil, France, Indonesia, and
   South Africa. Worldwide production was over 600 million metric tons in
   2003 – just slightly more than rice or wheat. In 2004, close to 33
   million hectares of maize were planted worldwide, with a production
   value of more than $23 billion.

   Because it is cold-intolerant, in the temperate zones maize must be
   planted in the spring. Its root system is generally shallow, so the
   plant is dependent on soil moisture. As a C4 plant (a plant that uses
   C4 photosynthesis), maize is a considerably more water-efficient crop
   than C3 plants like the small grains, alfalfa and soybeans. Maize is
   most sensitive to drought at the time of silk emergence, when the
   flowers are ready for pollination. In the United States, a good harvest
   was traditionally predicted if the corn was "knee-high by the Fourth of
   July", although modern hybrids generally exceed this growth rate. Maize
   used for silage is harvested while the plant is green and the fruit
   immature. Sweet corn is harvested in the "milk stage", after
   pollination but before starch has formed, between late summer and early
   to mid-autumn. Field corn is left in the field very late in the autumn
   in order to thoroughly dry the grain, and may, in fact, sometimes not
   be harvested until winter or even early spring. The importance of
   sufficient soil moisture is shown in many parts of Africa, where
   periodic drought regularly causes famine by causing maize crop failure.
   Field of maize in Liechtenstein
   Enlarge
   Field of maize in Liechtenstein

   Maize was planted by the Native Americans in hills, in a complex system
   known to some as the Three Sisters: beans used the corn plant for
   support, and squashes provided ground cover to stop weeds. This method
   was replaced by single species hill planting where each hill 60–120 cm
   (2–4 ft) apart was planted with 3 or 4 seeds, a method still used by
   home gardeners. A later technique was checked corn where hills were
   placed 40 inches apart in each direction, allowing cultivators to run
   through the field in two directions. In more arid lands this was
   altered and seeds were planted in the bottom of 10–12 cm (4–5 in) deep
   furrows to collect water. Modern technique plants maize in rows which
   allows for cultivation while the plant is young.
   A corn heap at the harvest site, India
   Enlarge
   A corn heap at the harvest site, India

   In North America, fields are often planted in a two- crop rotation with
   a nitrogen-fixing crop, often alfalfa in cooler climates and soybeans
   in regions with longer summers. Sometimes a third crop, winter wheat,
   is added to the rotation. Fields are usually plowed each year, although
   no-till farming is increasing in use. Nearly all maize cultivars grown
   in the United States and Canada are hybrids. Over half of the corn
   acreage planted in the United States has been genetically modified
   using biotechnology to express agronomic traits desired by farmers.

   Before about World War II, most maize was harvested by hand. This often
   involved large numbers of workers and associated social events. Some
   one- and two-row mechanical pickers were in use but the corn combine
   was not adopted until after the War. By hand or mechanical picker, the
   entire ear is harvested which then requires a separate operation of a
   corn sheller to remove the kernels from the ear. Whole ears of corn
   were often stored in corn cribs and these whole ears are a sufficient
   form for some livestock feeding use. Some modern farms store maize in
   this manner and later shell it for sale in the off-season to capture
   better prices. The combine with a corn head (with points and snap rolls
   instead of a reel) cuts the stalk near the base and then separates the
   ear of corn from the stalk so that only the ear and husk enter the
   machinery. The combine separates the husk and the cob, keeping only the
   kernels.

Pellagra

   Multicolored varieties of maize
   Enlarge
   Multicolored varieties of maize

   When maize was first introduced outside of the Americas it was
   typically welcomed enthusiastically by farmers everywhere for its
   productivity. However, a widespread problem of malnutrition soon arose
   wherever maize was introduced. This was a mystery since these types of
   malnutrition were not seen among the indigenous Americans under normal
   circumstances.

   It was eventually discovered that the indigenous Americans learned long
   ago to add alkali — in the form of ashes among North Americans and lime
   ( calcium carbonate) among Mesoamericans — to corn meal to liberate the
   B-vitamin niacin, the lack of which was the underlying cause of the
   condition known as pellagra. This alkali process is known by its
   Nahuatl (Aztec)-derived name: nixtamalization.

   Besides the lack of niacin, pellagra was also characterized by protein
   deficiency, a result of the inherent lack of two key amino acids in
   pre-modern maize, lysine and tryptophan. Nixtamalization was also found
   to increase the lysine and tryptophan content of maize to some extent,
   but more importantly, the indigenous Americans had learned long ago to
   balance their consumption of maize with beans and other protein sources
   such as amaranth and chia, as well as meat and fish, in order to
   acquire the complete range of amino acids for normal protein synthesis.

   Since maize had been introduced into the diet of non-indigenous
   Americans without the necessary cultural knowledge acquired over
   thousands of years in the Americas, the reliance on maize elsewhere was
   often tragic. Once alkali processing and dietary variety was understood
   and applied, pellagra disappeared. The development of high lysine maize
   and the promotion of a more balanced diet has also contributed to its
   demise.

Pests of maize

Insect pests

   Exotic varieties of maize are collected to add genetic diversity when
   selectively breeding new domestic strains.
   Enlarge
   Exotic varieties of maize are collected to add genetic diversity when
   selectively breeding new domestic strains.
     * Corn earworm (Helicoverpa zea)
     * Fall armyworm (Spodoptera frugiperda)
     * Common armyworm (Pseudaletia unipuncta)
     * Stalk borer (Papaipema nebris)
     * Corn leaf aphid (Rhopalosiphum maidis)
     * European corn borer (Ostrinia nubilalis) (ECB)
     * Corn silkfly (Euxesta stigmatis)
     * Lesser cornstalk borer (Elasmopalpus lignosellus)
     * Corn delphacid (Peregrinus maidis)

   The susceptibility of maize to the European corn borer, and the
   resulting large crop losses, led to the development of transgenic
   expressing the Bacillus thuringiensis toxin. "Bt corn" is widely grown
   in the United States and has been approved for release in Europe.

Diseases

     * Corn smut or common smut (Ustilago maydis): a fungal disease, known
       in Mexico as huitlacoche, which is prized by some as a gourmet
       delicacy in itself.
     * Maize Dwarf Mosaic Virus
     * Stewart's Wilt (Pantoea stewartii)
     * Common Rust (Puccinia sorghi)
     * Goss's Wilt (Clavibacter michiganese)
     * Grey Leaf Spot
     * Mal de Río Cuarto Virus (MRCV)

Uses for maize

   Corn shocks, or bundles, are a traditional harvest practice.
   Enlarge
   Corn shocks, or bundles, are a traditional harvest practice.

   In the United States and Canada, the primary use for maize is as a feed
   for livestock, forage, silage or grain. Silage is made by fermentation
   of chopped green cornstalks. The grain also has many industrial uses,
   including transformation into plastics and fabrics. Some is hydrolyzed
   and enzymatically treated to produce syrups, particularly high fructose
   corn syrup, a sweetener, and some is fermented and distilled to produce
   grain alcohol. Grain alcohol from maize is traditionally the source of
   bourbon whiskey. Increasingly ethanol is being used at low
   concentrations (10% or less) as an additive in gasoline ( gasohol) for
   motor fuels to increase the octane rating, lower pollutants, and reduce
   petroleum use.

   Human consumption of corn and cornmeal constitutes a staple food in
   many regions of the world. Corn meal is made into a thick porridge in
   many cultures: from the polenta of Italy and the mămăligă of Romania to
   mush in the U.S. or the food called sadza, nshima, ugali and mealie pap
   in Africa. It is the main ingredient for tortilla and many other dishes
   of Mexican food, and for chicha, a fermented beverage of Central and
   South America.

   Sweetcorn is a genetic variation that is high in sugars and low in
   starch that is served like a vegetable. Popcorn is kernels of certain
   varieties that explode when heated, forming fluffy pieces that are
   eaten as a snack.

   Maize can also be prepared as hominy, in which the kernels are bleached
   with lye; or grits, which are bleached coarsely ground corn. These are
   commonly eaten in U.S. Southern States, foods handed down from Native
   Americans. Another common food made from maize is corn flakes. The
   floury meal of maize ( cornmeal or masa) is used to make cornbread and
   Mexican tortillas. Teosinte is used as fodder, and can also be popped
   as popcorn.

   Some forms of the plant are occasionally grown for ornamental use in
   the garden. For this purpose, variegated and coloured leaf forms as
   well as those with colourful cobs are used. Additionally,
   size-superlative varieties, having reached 31 ft (9m) tall [Evening
   Journal, Washington Iowa 1946], or with cobs 24 inches long [Kempton
   1924], have been popular for at least a century .

   Corn male flower, a.k.a. corn tassel
                                Enlarge
   Corn male flower, a.k.a. corn tassel

                                       Corn female flower, a.k.a. corn silk
                                                                    Enlarge
                                       Corn female flower, a.k.a. corn silk

   Corncobs can be hollowed out and treated to make inexpensive smoking
   pipes, first manufactured in the United States in 1869. Corn cobs are
   also used as a biomass fuel source. Maize is relatively cheap and
   home-heating furnaces have been developed which use maize kernels as a
   fuel. They feature a large hopper which feeds the uniformly sized corn
   kernels (or wood pellets or cherry pits) into the fire.

   An unusual use for maize is to create a Maize Maze as a tourist
   attraction. This is a maze cut into a field of maize. The idea of a
   Maize Maze was introduced by Adrian Fisher, one of the most prolific
   designer of modern mazes, with The American Maze Company who created a
   maze in Pennsylvania in 1993. Traditional mazes are most commonly grown
   using yew hedges, but these take several years to mature. The rapid
   growth of a field of maize allows a maze to be laid out using GPS at
   the start of a growing season and for the maize to grow tall enough to
   obstruct a visitor's line of sight by the start of the summer. In
   Canada and the U.S., these are called "corn mazes" and are popular in
   many farming communities.

   In 1983, Barbara McClintock received the Nobel Prize in Physiology or
   Medicine for discovery of transposons while studying maize. Maize is
   still an important model organism for genetics and developmental
   biology today.

   Maize is sometimes used as a biomass fuel, such as ethanol . A biomass
   gasification power plant in Strem near Güssing, Burgenland, Austria was
   begun in 2005. Research is being done to make diesel out of the biogas
   by the Fischer Tropsch method.

   Maize is also used as fish bait. It is particularly popular in Europe
   for coarse fishing.

   Stigmas from female corn flowers, known popularly as corn silk, are
   sold as herbal supplements.

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