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Cultivars of maize
Cultivars of maize
While certain maize varieties grow 7 m (23 ft) tall at certain locations, commercial maize has been bred for a high-end height of 2.5 m (9 ft). Sweet corn is usually shorter than field corn varieties.
The stems look like bamboo cane and the joints are about 40–50 cm (16–20 inches) 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 feet by 2–4 inches); the stems are erect, from 2–3 m (7–10 feet) in height, with many joints, casting off flag-leaves at every joint. Under these leaves and close to the stem grows the corn, covered over by several layers of leaves, and so closed in by them to the stem, that it does not show itself easily till there bursts out at the end of the ear a number of strings, called silk, that look like tufts of horsehair, at first green, and afterwards red or yellow. The top of the stem ends in a flower, called the tassle. For each silk on which pollen from the tassle lands, one kernel of corn is produced. Young ears can be consumed raw, cob, silk, and all; as the plant matures (usually during the summer months) the cob toughens 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 inches) in length. They are of various colors, blackish, red, white and yellow. When ground into flour, it yields more flour, with much less bran, than wheat does. However, it lacks the protein gluten, and therefore makes baked goods with poor raising capability.
Origin of maize
Maize is a direct domesticate of the 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. The term teosinte describes all species in the genus Zea, excluding Zea mays ssp. mays.
Maize development is thought to have started from 7,500 to 12,000 years ago. Archaeological remains of the earliest maize cob, found at Guila Naquitz Cave in the Oaxaca Valley of Mexico, date back roughly 6,250 years.
As a historical note, in the late 1930s, Paul Mangelsdorf suggested that domesticated maize was the result of a hybridization event between an unknown wild maize and Tripsacum. However, the proposed role of the related genus Tripsacum in the origins of maize has been refuted by modern genetic analysis.
The domestication of maize is of particular interest to researchers. It is unknown what precipitated its domestication, because the edible portion of the wild variety is too small to be worthwhile cultivating. It would have taken many generations of selective breeding in order to produce a plant with cobs large enough to eat.
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, India, Brazil, France, Indonesia, and South Africa. Worldwide production was over 600 million metric tons in 2003, just slightly more than rice or wheat.
Maize is planted in the spring to take advantage of spring rains. Its root system is shallow and the plant is dependent on steady rain or irrigation. In the United States, a good harvest was predicted traditionally if the corn was "knee-high by the Fourth of July", although modern hybrids often exceed this growth rate. Maize used as silage is harvested while the plant is green and the fruit unmatured. Otherwise, maize is left in the field very late in the autumn in order to dry thoroughly. In fact, it is sometimes not harvested until winter or even early spring. The importance of regular rain is shown in many parts of Africa, where periodic drought regularly causes famine by causing maize crop failure; the older traditional African native millet (which is however less palatable than maize, and much less productive in good years) would have survived and produced a small crop in these conditions.
Maize was planted by the Native Americans in hills, in a complex system known to some as the Three Sisters in which beans used the corn plant for support and squashes which provided ground cover to stop weeds. This method was replaced by single species hill planting where each hill 60–120 cm (2–4 feet) apart was planted with 3 or 4 seeds, a method still used by the home gardener. 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 seed were planted in the bottom of 10–12 cm (4–5 inch) deep furrows to collect water. Modern technique plants maize in rows which allows for cultivation while the plant is young.
In North America, fields are often planted in a two crop rotation with a nitrogen-fixing crop, often soybeans. 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.
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 did not get 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 which is a sufficient form for some livestock 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.
Pests of maize
- Corn earworm (Heliothis zea)
- Fall armyworm (Spodoptera frugiperda)
- Common armyworm (Pseudaletia unipuncta)
- Stalk borer (Papaipema nebris)
- Corn leaf aphid (Rhopalosiphum maidis)
- European corn borer (Ostrinia nubilalis) (ECB), the susceptibility of maize to the ECB and large crop losses led to the development of transgenic corn expressing the Bt toxin. BtCorn is widely grown in the United States and has been approved for release in Europe.
- Corn silkfly (Euxesta stigmatis)
- Lesser cornstalk borer (Elasmopalpus lignosellus)
- Corn delphacid (Peregrinus maidis)
- 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)
Uses for maize
The primary use for corn (seed) in United States and Canada, is as a feed for livestock, while some is for the production of corn sweeteners like corn syrup, and the production of ethanol. Ethanol, a type of alcohol, is mostly used as an additive in gasoline to increase the octane rating.
Human consumption of corn and corn meal constitute only a very small percentage of the United States and Canada production, but in Mexico its use for human consumption is very important as it is the main ingredient for Tortilla and many other dishes of Mexican food.
Maize can also be prepared as hominy, in which the kernels are bleached with lye; or grits, which are simply 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 flour of maize is used to make cornbread and Mexican tortillas. Teosinte is used as fodder, and can also be popped as popcorn.
- 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
- Pod corn - Zea mays L. var. tunicata Larra�aga ex A. St. Hil
Many scientists speculate that fuel ethanol will mostly be produced from switchgrass and other biomass sources in the future. Corn cobs are also used as a biomass fuel source. Maize is relatively cheap and home heating furnaces have been developed which uses 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.
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.
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.  (http://www.srs.fs.usda.gov/about/newsrelease/nr_2005-06-06-mussels.htm)