Maize (Zea mays L. ssp. mays ) known in many English-speaking countries as corn or mielie/mealie, is a grain domesticated by indigenous peoples in Mesoamerica in prehistoric times. The leafy stalk produces ears which contain seeds called kernels. Maize kernels are technically a fruit but are used in cooking as a vegetable or starch.
The Olmec and Mayans cultivated it in numerous varieties throughout central and southern Mexico, cooked, ground or processed through nixtamalization. Between 1700 and 1250 BCE, the crop spread through much of the Americas. The region developed a 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. Maize spread to the rest of the world due to its ability to grow in diverse climates.
Sugar-rich varieties called sweet corn are usually grown for fresh consumption while field-corn varieties are used for animal feed and as chemical feedstocks.
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
Many small male flowers make up the male inflorescence, called the tassel
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. Though it should be noted that within the United States, the term “maize” is almost totally unheard of. “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.
Structure and physiology
Maize stems superficially resemble bamboo canes and the internodes can reach 44.5 centimetres (17.5 in).
Maize has a distinct growth form; the lower leaves being like broad flags, generally 50–100 centimetres long and 5–10 centimetres wide (2–4 ft by 2–4 in); the stems are erect, conventionally 2–3 metres (7–10 ft) in height,
Female inflorescence, with young silk
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 millimetres a day.
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. Plantings for silage are even denser, and achieve a lower percentage of ears and more plant matter.
Certain varieties of maize have been bred to produce many additional developed ears. These are the source of the “baby corn” used as a vegetable in Asian cuisine.
Maize is a facultative long-night plant and flowers in a certain number of growing degree days > 50 °F (10 °C) in the environment to which it is adapted.
The magnitude of the influence that long nights have on the number of days that must pass before maize flowers is genetically prescribed and regulated by the phytochrome system.
Photoperiodicity can be eccentric in tropical cultivars, while the long days characteristic of higher latitudes allow the plants to grow so tall that they do not have enough time to produce seed before being killed by frost.
Male flowers
These attributes, however, may prove useful in using tropical maize for biofuels.
The apex of the stem ends in the tassel, an inflorescence of male flowers. When the tassel is mature and conditions are suitably warm and dry, anthers on the tassel dehisce and release pollen. Maize pollen is anemophilous (dispersed by wind) and because of its large settling velocity most pollen falls within a few meters of the tassel. Each silk may become pollinated to produce one kernel of maize. 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 the end of the growing season, the kernels dry out and become difficult to chew without cooking them tender first in boiling water. Modern farming techniques in developed countries usually rely on dense planting, which produces one large ear per stalk.
Seeds
Maize kernels
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-methoxy1,4-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.
