Cultivation of maize | maize Insects | maize Diseases | Corn

Corn
Maize, known in many English-speaking countries as corn, is a grain domesticated by indigenous peoples in Mesoamerica in prehistoric times. The Aztecs and Mayans cultivated it in numerous varieties throughout central and southern Mexico, to cook or grind in a process called nixtamalization. Later, the crop spread through much of the Americas. Between 1700 and 1250 BCE, the crop spread to all corners of the region. Any significant or dense populations in the region developed a great trade network based on surplus and varieties of maize crops. After European contact with the Americas in the late 15th and early 16th centuries, explorers and traders carried maize back to Europe and introduced it to other countries through trade. Maize spread to the rest of the world due to its popularity and ability to grow in diverse climates.

Maize is the most widely grown crop in the Americas with 332 million metric tons grown annually in the United States alone (although 40% of the crop - 130 million tons - is used for corn ethanol. Transgenic maize made up 85% of the maize planted in the United States in 2009. While some maize varieties grow to 12 metres (39 ft) tall, most commercially grown maize has been bred for a standardized height of 2.5 metres (8.2 ft). Sweet corn is usually shorter than field-corn varieties.

Naming conventions

The term 'maize' derives from the Spanish form of the indigenous Taino word maiz for the plant. This was the term used in the United Kingdom and Ireland, where it is now usually called "sweet corn", the most common form of the plant known to people there. Sweet corn is harvested earlier and eaten as a vegetable rather than a grain.

Outside the British Isles, another common term for maize is "corn". This was originally the English term for any cereal crop. In North America, its meaning has been restricted since the 19th century to maize, as it was shortened from "Indian corn." The term Indian corn now refers specifically to multi-colored "field corn" (flint corn) cultivars.

In scientific and formal usage, "maize" is normally used in a global context. Equally, in bulk-trading contexts, "corn" is used most frequently. In the UK, Australia and other English-speaking countries, the word "corn" is often used in culinary contexts, particularly in naming products such as popcorn and corn flakes. "Maize" is used in agricultural and scientific references.

In Southern Africa, maize is commonly referred to as mielie or mealie, from the Portuguese milho. Mielie-meal is the ground form.

Seeds

The kernel of maize has a pericarp of the fruit fused with the seed coat, typical of the grasses, and the entire kernel is often referred to as the seed. The cob 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 200 to 400 kernels, and is from 10–25 cm (4–10 in) in length. They are of various colors: blackish, bluish-gray, purple, green, 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 variant that accumulates more sugar and less starch in the ear is consumed as a vegetable and is called sweet corn.

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 be attacked 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.

Because of its shallow roots, maize is susceptible to droughts, intolerant of nutrient-deficient soils, and prone to be uprooted by severe winds.

Production

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 carbon fixation), maize is a considerably more water-efficient crop than C3 plants (plants that use C3 carbon fixation) 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 maize 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 maize 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.

Many of the maize varieties grown in the United States and Canada are hybrids. Often the varieties have been genetically modified to tolerate glyphosate or to provide protection against natural pests. Glyphosate (trade name Roundup) is an herbicide which kills all plants except those with genetic tolerance. This genetic tolerance is very rarely found in nature.

Quantity

Maize is widely cultivated throughout the world, and a greater weight of maize is produced each year than any other grain. The United States produces 40% of the world's harvest; other top producing countries include China, Brazil, Mexico, Indonesia, India, France and Argentina. Worldwide production was 817 million tonnes in 2009—more than rice (678 million tonnes) or wheat (682 million tonnes).[24] In 2009, over 159 million hectares of maize were planted worldwide, with a yield of over 5 tonnes/hectare. Production can be significantly higher in certain regions of the world; 2009 forecasts for production in Iowa were 11614 kg/ha. "There is conflicting evidence to support the hypothesis that maize yield potential has increased" over the past few decades.

Insects
  • 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)
  • Western corn rootworm (Diabrotica virgifera virgifera LeConte)
  • Southwestern corn borer (Diatraea grandiosella)
  • Maize weevil (Sitophilus zeamais)
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.
  • Northern leaf blight
  • Southern lead blight
  • Maize dwarf mosaic virus
  • Maize streak virus
  • Stewart's Wilt (Pantoea stewartii)
  • Common Rust (Puccinia sorghi)
  • Goss's Wilt (Clavibacter michiganese)
  • Grey Leaf Spot
  • Mal de Río Cuarto Virus (MRCV)
  • Stalk Rot
  • Ear Rot
Scientific classification
Kingdom: Plantae
(unranked): Commelinids
Order: Poales
Family: Poaceae
Subfamily: Panicoideae
Tribe: Andropogoneae
Genus: Zea
Species: Z. mays


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