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M A I Z E - ZEA MAYS


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Bianca
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« on: November 07, 2008, 09:03:33 am »




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Bianca
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« Reply #1 on: November 07, 2008, 09:07:04 am »










                                             M A I Z E  -  Z E A   M A Y S (Latin)






Maize (IPA: /ˈmeɪz/) (Zea mays L. ssp. mays), known as corn in some countries, is a cereal grain domesticated in Mesoamerica and subsequently spread throughout the American continents. After European contact with the Americas in the late 15th and early 16th century, maize spread to the
rest of the world.

Maize is the most widely grown crop in the Americas (270 million tonnes annually in the United States alone). Hybrid maize, due to its high grain yield as a result of heterosis ("hybrid vigour"), is preferred
by farmers over conventional varieties. While some maize varieties grow up to 7 metres (23 ft) tall,  most commercially grown maize has been bred for a standardized height of 2.5 metres (8 ft).

Sweet corn is usually shorter than field-corn varieties.
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« Reply #2 on: November 07, 2008, 09:09:51 am »



                                

                                 Female flower, called silk
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« Reply #3 on: November 07, 2008, 09:14:58 am »










The term maize derives from the Spanish form (maνz) of the indigenous Taino term for the plant, and is the form most commonly heard in the United Kingdom.[2] In the United States, Canada and Australia, the usual term is corn, which originally referred to any grain (and still does in Britain), but which now refers exclusively to maize, having been shortened from the form "Indian corn" (which currently, at least in the U.S., is often used to refer specifically to multi-colored "field corn" cultivars).[3]



Maize stems superficially resemble bamboo canes and the internodes can reach 20–30 centimetres
(8–12 in). Maize has a very distinct growth form; the lower leaves being like broad flags, 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, 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 milimetres 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 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.
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« Reply #4 on: November 07, 2008, 09:16:39 am »




                                  

                                    Male flower, called the tassel
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« Reply #5 on: November 07, 2008, 09:28:39 am »










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 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 on average only about 0.9 ears per stalk because it stresses the plants.

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 200 to 400 kernels, and is from 10–25 centimetres (4–10 inches) 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 and coherence.

A genetic variation 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.
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« Reply #6 on: November 07, 2008, 09:30:13 am »




                               

                                Stalks, ears, and silk
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« Reply #7 on: November 07, 2008, 09:36:00 am »










Many forms of maize are used for food, sometimes classified as various subspecies:



Flour corn — Zea mays var. amylacea

Popcorn — Zea mays var. everta

Dent corn — Zea mays var. indentata

Flint corn — Zea mays var. indurata

Sweet corn — Zea mays var. saccharata and Zea mays var. rugosa

Waxy corn — Zea mays var. ceratina

Amylomaize — Zea mays

Pod corn — Zea mays var. tunicata Larraρaga ex A. St. Hil.

Striped maize - Zea mays var. japonica



This system has been replaced (though not entirely displaced) 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": 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", for which she won the 1983 Nobel Prize in Physiology or Medicine. Maize is still an important model organism for genetics and developmental biology today.

There is a stock center of maize mutants, The Maize Genetics Cooperation — Stock Center, 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.)

On February 26, 2008, researchers announced that they had sequenced the entire genome of maize.
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« Reply #8 on: November 07, 2008, 09:38:08 am »



Tripsacum grass (big) and a teosinte (small)
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« Reply #9 on: November 07, 2008, 09:42:34 am »










                                                            O R I G I N





 
There are several theories about the specific origin of maize in Mesoamerica:



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.

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.

It underwent two or more domestications either of a wild maize or of a teosinte.

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 testing, refuting Mangelsdorf’s model and the fourth listed above.



The first model was proposed by Nobel Prize winner George Beadle in 1939.

Though it has experimental support, it has not explained a number of problems, among them:



how the immense diversity of the species of sect. Zea originated,

how the tiny archaeological specimens of 3500–2700 BCE (uncorrected) could have been selected
from a teosinte, and

how domestication could have proceeded without leaving remains of teosinte or maize with teosintoid traits until ca. 1100 BCE.
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« Reply #10 on: November 07, 2008, 09:43:49 am »



Guila Naquitz Cave,
site of the oldest known remains of maize
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« Reply #11 on: November 07, 2008, 09:48:51 am »









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 9,000 years ago in central Mexico, perhaps in the highlands between Oaxaca and Jalisco.

The crop wild relative teosinte most similar to modern maize grows in the area of the Balsas River.

Archaeological remains of early maize ears, found at Guila Naquitz Cave in the Oaxaca Valley, date back roughly 6,250 years (corrected; 3450 BCE, uncorrected); the oldest ears from caves near Tehuacan, Puebla, date ca. 2750 BCE. Little change occurred in ear form until ca. 1100 BCE when great changes appeared in ears from Mexican caves: maize diversity rapidly increased and archaeological teosinte was first deposited.

Perhaps as early as 1500 BCE, 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.

The Mesoamerican civilization was strengthened upon the field crop of maize; through harvesting it, its religious and spiritual importance and how it impacted their diet. Maize formed the Mesoamerican people’s identity. During the 1st millennium CE (AD), maize cultivation spread from Mexico into the U.S. Southwest and a millennium later into U.S. Northeast and southeastern Canada, transforming the landscape as Native Americans cleared large forest and grassland areas for the new crop.

 
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 what is now the southeastern United States contributed to the decline of freshwater mussels, which are very sensitive to environmental changes.
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« Reply #12 on: November 07, 2008, 09:52:35 am »









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 in turn provided nitrogen from nitrogen-fixing bacteria which live on the roots of beans and other legumes; and

- squashes provided ground cover to stop weeds and inhibit evaporation by providing shade over the soil.



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, although the hill technique is still used in the cornfields of some Native American reservations.



FROM


wikipedia.org
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« Reply #13 on: November 07, 2008, 09:56:44 am »









Pellagra



When maize was first introduced outside of the Americas it was generally welcomed with enthusiasm
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. Nixtamalisation 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.

In the late 19th century pellagra reached endemic proportions in parts of the deep southern U.S., as medical researchers debated two theories for its origin:

the deficiency theory (eventually shown to be true) posited that pellagra was due to a deficiency of some nutrient, and

the germ theory posited that pellagra was caused by a germ transmitted by stable flies.



In 1914 the U.S. government officially endorsed the germ theory of pellagra, but rescinded this endorsement several years later as evidence grew against it.

By the mid-1920s the deficiency theory of pellagra was becoming scientific consensus, and the
theory was proved in 1932 when niacin deficiency was determined to be the cause of the illness.

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.



http://en.wikipedia.org/wiki/Maize
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« Reply #14 on: November 07, 2008, 10:10:15 am »










                           Picking The Perfect Ear Of Corn -- For More Than 6,000 Years






ScienceDaily
(June 22, 2005) —

Those ears of sweet, crisp corn that are such a familiar part of summertime picnics haven't always looked or tasted that way. Rather, this staple veggie--and its genes--have been tweaked over time by thousands of generations of humans hoping to harvest a better crop.

Now, an Agricultural Research Service geneticist and his colleagues from across the country have discovered what impact all those years of preferential planting have had on corn's genetic makeup.

In a recent issue of the journal Science, the scientists report their discoveries on which genes play a role in making corn the important food and animal feed source we know today. Michael McMullen, a geneticist in ARS' Plant Genetics Research Unit at Columbia, Mo., worked with lead author Brandon Gaut of the University of California, Irvine, and scientists from the University of Missouri and the University of Wisconsin.

It's generally believed that corn was domesticated from its wild relative, teosinte, some 6,000 to 9,000 years ago in Mexico. A wild grass, teosinte doesn't look much like corn; it even lacks the "ears" that make corn plants so recognizable.

The researchers discovered that humans, starting with ancient Americans to present-day growers, have impacted about 2 to 4 percent of corn's genes in their quest for a better-tasting and more cultivatable corn crop. The scientists believe the affected genes are most likely linked to qualities like growth and yield.

Their work has many implications, including establishing an approach for studying the genetics of domestication of other crops and animals.

The research also indicates that while a large amount of genetic diversity still remains for the vast majority of corn's genes--enabling future corn improvement by plant breeders--knowing the 2 to 4 percent currently lacking genetic variation will help plant geneticists use wild and exotic corn varieties to continually improve this important crop.

This collaborative research was funded by the National Science Foundation's Plant Genome Research Program.

ARS is the chief scientific research agency of the U.S. Department of Agriculture.


--------------------------------------------------------------------------------

Adapted from materials provided by USDA / Agricultural Research Service.
Need to cite this story in your essay, paper, or report? Use one of the following formats:
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 MLA USDA / Agricultural Research Service (2005, June 22). Picking The Perfect Ear Of Corn -- For More Than 6,000 Years. ScienceDaily.





Retrieved September 29, 2008, from


http://www.sciencedaily.com­ /releases/2005/06/050619194524.htm
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