A cultigen (from the Latin cultus - cultivated, and gens - kind) is a plant that has been deliberately altered or selected by humans; it is the result of artificial selection. These "man-made" or anthropogenic plants are, for the most part, plants of commerce that are used in horticulture, agriculture and forestry. Because cultigens are defined by their mode of origin and not by where they are growing, plants meeting this definition remain cultigens whether they are naturalised in the wild, deliberately planted in the wild, or growing in cultivation. Cultigens arise in the following ways: selections of variants from the wild or cultivation including vegetative sports (aberrant growth that can be reproduced reliably in cultivation); plants that are the result of plant breeding and selection programs; genetically modified plants (plants modified by the deliberate implantation of genetic material); and graft-chimaeras (plants grafted to produce mixed tissue, the graft material possibly from wild plants, special selections, or hybrids).

Cultigens may be named in any of a number of ways. The traditional method of scientific naming is under the International Code of Botanical Nomenclature, and many of the most important cultigens, like maize (Zea mays) and banana (Musa acuminata), are so named. Although it is perfectly in order to give a cultigen a botanical name, in any rank desired, now or at any other time,^[1] these days it is more common for cultigens to be given names in accordance with the principles, rules and recommendations laid down in the Cultivated Plant Code which provides for the names of cultigens in three classification categories, the cultivar, the Group (formerly Cultivar-group), and the grex.^{[nb 1]} From that viewpoint it may be said that there is a separate discipline of cultivated plant taxonomy, which forms one of the ways to look at cultigens. The Cultivated Plant Code does not recognize the use of trade designations and other marketing devices as scientifically acceptable names.^[2]

Not all cultigens have been given names according to the Cultivated Plant Code. Apart from ancient cultigens like those mentioned above there may be occasional anthropogenic plants such as those that are the result of breeding, selection, and tissue grafting that are of no commercial value and have therefore not been given names according to the Cultivated Plant Code.

Formal definition

A cultigen is a plant whose origin or selection is primarily due to intentional human activity.^[3]

The distinction "wild" and "cultivated"

Interest in the distinction between wild and cultivated plants dates back to antiquity. Botanical historian Alan Morton notes that wild and cultivated plants (cultigens) were of intense interest to the ancient Greek botanists (partly for religious reasons) and that the distinction was discussed in some detail by Theophrastus (370–285 BCE) the "Father of Botany". Theophrastus was a pupil of both Plato and Aristotle and succeeded the latter as head of the Peripatetic School of Philosophy at the Lyceum in Athens. Theophrastus accepted the view that it was human action not divine intervention that produced cultivated plants (cultigens) from wild plants and he also "had an inkling of the limits of culturally induced (phenotypic) changes and of the importance of genetic constitution" (Historia Plantarum III, 2,2 and Causa Plantarum I, 9,3). He also noted that cultivated varieties of fruit trees would degenerate if cultivated from seed.^[4]

Origin of term

Liberty Hyde Bailey 1858-1954, who coined the word cultigen in 1918

The word cultigen was coined in 1918^[5] by Liberty Hyde Bailey (1858–1954) an American horticulturist, botanist and cofounder of the American Society for Horticultural Science. He was aware of the need for special categories for those cultivated plants that had arisen by intentional human activity and which would not fit neatly into the Linnaean hierarchical classification of ranks used by the International Code of Botanical Nomenclature (Cultivated Plant Code).

In his 1918 paper Bailey noted that for anyone preparing a descriptive account of the cultivated plants of a country (he was at that time preparing such an account for North America) it would be clear that there are two gentes or kinds (Latin singular, gens; plural, gentes) of plants. Firstly, those that are of known origin or nativity "of known habitat". These he referred to as indigens. The other kind was:

" ... a domesticated group of which the origin may be unknown or indefinite, which has such characters as to separate it from known indigens, and which is probably not represented by any type specimen or exact description, having therefore no clear taxonomic beginning."

He called this second kind of plant a cultigen, the word derived from the conflation of the Latin cultus - cultivated, and gens - kind.

In 1923 ^[6] Bailey extended his original discussion emphasising that he was dealing with plants at the rank of species and he referred to indigens as:

Wikisource has original works written by or about: L. H. Bailey

" those that are discovered in the wild "

and cultigens as plants that:

" arise in some way under the hand of man "

He then defined a cultigen as:

"... a species, or its equivalent, that has appeared under domestication ..."

Bailey's definitions

Bailey soon altered his 1923 definition of cultigen when, in 1924, he gave a new definition in the Glossary of his Manual of Cultivated Plants^[7] as:

" Plant or group known only in cultivation; presumably originating under domestication; contrast with indigen "

This, in essence, is the definition given at the head of this piece. This definition of the cultigen permits the recognition of cultivars, unlike the 1923 definition which restricts the idea of the cultigen to plants at the rank of species.

In later publications of the Liberty Hyde Bailey Hortorium, Cornell, the idea of the cultigen having the rank of species returned (e.g. Hortus Second in 1941 and Hortus Third in 1976):^[8][9] both of these publications indicate that the terms cultigen and cultivar are not synonymous and that cultigens exist at the rank of species only.

"A cultigen is a plant or group of apparent specific rank, known only in cultivation, with no determined nativity, presumably having originated, in the form in which we know it, under domestication. Compare indigen. Examples are Cucurbita maxima, Phaseolus vulgaris, Zea mays'".

Recent usage in horticulture has, however, maintained a distinction between cultigen and cultivar while nevertheless allowing the inclusion of cultivars within the definition (see "Usage in horticulture" below).

Cultigens and cultivars

Cultigen and cultivar may be confused with one another. Cultigen is a general-purpose term encompassing not only plants with cultivar names but others as well (see introductory text above), while cultivar is a formal classification category (in the ICNCP).

Although in his 1923 paper Bailey used only the rank of species for the cultigen, it was clear to him that many domesticated plants were more like botanical varieties than species and so he established a new classification category for these, the cultivar, generally assumed to be a contraction of the words “cultivated” and “variety”. Bailey was never explicit about the etymology of the word cultivar and it has been suggested that it is a contraction of the words “cultigen” and “variety”.^[10] He defined cultivar in his 1923 paper as:

... " a race subordinate to species, that has originated and persisted under cultivation; it is not necessarily, however, referable to a recognised botanical species. It is essentially the equivalent of the botanical variety except in respect to its origin ".

This definition and understanding of cultivar has changed over time (see current definition in cultivar).

Usage

Usage in botany

In botanical literature the word cultigen is generally used to denote a plant which, like the wheat (Triticum aestivum) is of unknown origin, but presumed to be an ancient human selection. Plants like these have been given binomials according to the Botanical Code and therefore have names that have the same form as those of plants that occur naturally in the wild. As these cultigens are the result of deliberate human selection there is no difference, in principle, between them and modern plants with additional names under the Cultivated Plant Code. The use of binomials for cultigens occurs for the most part because they were following the accepted nomenclatural conventions that pre-dated the Cultivated Plant Code. In theory cultigens can be named under either Code or both, although in practice almost all have cultivar names governed by the Cultivated Plant Code.

Usage in horticulture

Cabbage
Cabbage, cultivar unknown
Details
Species	Brassica oleracea
Cultivar group	Capitata Group
Origin	Mediterranean, 1st century
Cultivar group members	Many

The year 1953 was an important one for cultivated plant taxonomy because this was the date of publication of the first International Code of Nomenclature for Cultivated Plants in which Bailey’s term cultivar was introduced. It was also the year that the eponymous journal commemorating the work of Bailey (who died in 1954), Baileya, was published. In the first volume of Baileya taxonomist and colleague of Bailey, George Lawrence, wrote a short article clarifying the distinction between the new term cultivar and the variety. In the same article he also tried to clarify the critical term taxon which had been introduced by German biologist Meyer in the 1920s but had only just been introduced and accepted in botanical circles. This brief article by Lawrence is useful for its insight into the understanding of the meaning of the word cultigen at this time. He opens the article:

In 1918, L.H. Bailey distinguished those plants originating in cultivation from the native plants by designating the former as cultigens and the latter as indigens (indigenous or native to the region). At the same time he proposed the term cultivar to distinguish varieties originating in cultivation from botanical varieties known first in the wild.^[11]

In horticulture the definition and use of the term cultigen has varied but generally, unlike usage in botany, it encompasses cultivars. One example is the definition given in the Botanical Glossary of The New Royal Horticultural Society Dictionary of Gardening^[12] which defines cultigen as:

" A plant found only in cultivation or in the wild having escaped from cultivation; included here are many hybrids and cultivars, "...

The use of cultigen in this sense is essentially the same as the definition of the cultigen published by Bailey in 1924.

Other usage

The term cultigen is occasionally applied in a very general sense to any organisms that do not have a wild or uncultivated counterpart, see for example.^[13] Animal breeds raised in captivity would be included here. It might seem that the word "domesticate" could serve the same purpose as cultigen. However, the widely held view that domesticated plants and animals are simply wild plants and animals used in domestic situations (often as tamed wild animals, or plants introduced directly from the wild, rather than being specially selected for particular desirable characteristics) would not support this view. However there is debate about what constitutes domestication and some authors maintain that to be termed domesticated or a "domesticate" a plant or animal must have been genetically "changed" in some way from its wild counterparts, either by conscious or unconscious selection.^[14] Regardless of this debate, it is clear that the term cultigen originated within horticulture and botany and that these areas are where it has mostly been applied.

Recommended usage

Wider use of the term cultigen as defined here has been proposed ^[3] for the following reasons:

• supports current usage in horticulture
• assists clarity in non-technical discussions about “wild” and “cultivated” plants (for example, cultivated plants as commonly understood (plants in cultivation) are not the same as the "cultivated plants" of the Cultivated Plant Code, and the distinction between "wild" and "cultivated" habitats is becoming progressively blurred)
• has the potential to simplify the language and definitions used in the Articles and Recommendations of the Cultivated Plant Code
• gives greater precision and clarity to the definition of the respective scope, terminology and concepts of the Botanical Code and the Cultivated Plant Code
• avoids the potential for confusion within the Cultivated Plant Code over its scope, that is, whether it is concerned with:

• where plants are growing (in the wild or in cultivation)
• how they originated (whether they are the result of intentional human activity or not)
• whether it simply provides a mechanism for regulating the names of those cultigens requiring special classification categories that are not part of the Linnaean hierarchy of the Botanical Code i.e. cultivar and Group names ^[3][15]

Critique of definition

Pedunculate Oak
Leaves and acorns; note the long acorn stems
Conservation status
Least Concern (IUCN 3.1)
Scientific classification
Kingdom:	Plantae
Phylum:	Magnoliophyta
Class:	Magnoliopsida
Order:	Fagales
Family:	Fagaceae
Genus:	Quercus
Section:	Quercus
Species:	Q. robur
Binomial name
Quercus robur L.

Potential misunderstandings and questions arising from the definition of cultigen given here have been discussed in the literature^[15] and are summarised below.

• Natural and artificial selection

The selection process is termed "artificial" when human preferences or influences have a significant effect on the evolution of a particular population or species (see artificial selection). Note: artificial selection is a part of the overall selection process - it does not imply that humans are not part of nature, it is simply useful sometimes to distinguish when there has been human influence on selection (as with cultigens).

• What exactly does altered mean?

There are cases that do not seem to comply with the definition. For example, we can presume that the entire global flora is changing as a result of human-induced climate change. Does this mean that all plants are cultigens?

In cases like this the definition refers to "deliberate" selection and this would be of particular plant characteristics that are not exhibited by a plant's wild counterparts (but see Selections from the wild).

• What exactly does deliberately selected mean?

From the moment a plant is taken from the wild it is subject to human selection pressure - from the selection of the original propagation material to the purchase of the plant in a nursery. Surely this form of selection is not deliberate? Again, the early human selection of crops 7,000-10,000 years ago is thought to have occurred quite unintentionally. Variants useful to horticulture often arise spontaneously, they are not deliberate products. Are these cases of unintentional, accidental, or unconscious selection?

There certainly appear to be cases where origin or selection of a plant is not "deliberate". However, the long term propagation of plants that have some utility, usually economic or ornamental, can hardly be regarded as unintentional and these plants will, almost without exception, have characteristic(s) that distinguish them from their wild counterparts.

• What about plants selected from the wild?

Plants like Quercus robur, Pedunculate or English Oak, Liquidambar styraciflua, Sweetgum and Eucalyptus globulus, Blue Gum grown in parks and gardens are essentially the same as their wild counterparts and are therefore not cultigens. However, occasionally within natural plant variation there occur characters that are of value to horticulture but of little interest to botany. For example a plant might have flowers of several different colours but these may not have been given formal botanical names. It is customary in horticulture to introduce such variants to commerce and to give them cultivar names. Technically these plants have not been deliberately altered in any way from plants growing (or once growing) in the wild but as they are deliberately selected and named it seems permissible to refer to them as cultigens. These occurrences are very few. The definition could be (clumsily) extended by mentioning that selection can be for "desirable variation that is not recognised in botanical nomenclature" (which excludes those plants simply transferred from the wild into cultivation).

• What about gene flow between populations?

Occasionally cultigens escape from cultivation into the wild where they breed with indigenous plants. Selections may be made from the progeny in the wild and brought back into cultivation where they are used for breeding and the results of the breeding again escape into the wild to breed with indigenous plants. Lantana has behaved much like this. The genetic material of a cultigen may become part of the gene pool of a population where, over time, it may be largely or completely swamped. In cases like this what plants are to be called cultigens?

Whether a plant is a cultigen or not does not depend on where it is growing. If it complies with the definition then it is a cultigen. Cases like this have always been difficult for botanical nomenclature. Unnamed progeny in the wild might be given a name like Lantana aff. camara (aff. = having affinities with) or may remain unnamed. Its cultigenic origin may or may not be recognised by the allocation of a cultivar name.

• Plants of unknown origin

Occasionally plants will occur whose origin is unknown. Plants growing in cultivation that are unknown in the wild may be determined as cultigenic as a result of scientific investigation, but may remain a mystery.

• Difficult cases

It may happen that a hybrid cross that has occurred in nature is also performed deliberately in cultivation and that the progeny appear identical. How do we know which plants are cultigens?

If the cross in cultivation is followed by deliberate selection and naming then this will indicate a cultigen. However in a case like this it may not be possible to tell.

See also

References

Footnotes

1. ^ The category grex was added in the 2009 Cultivated Plant Code and applies only to orchids

Further reading

• Spencer, R.D. and Cross, R.G. 2007. The International Code of Botanical Nomenclature (ICBN), the International Code of Nomenclature for Cultivated Plants (ICNCP), and the cultigen. Taxon 56(3):938-940

• Spencer, R, Cross, R & Lumley, P. 2007. (3rd edn) Plant names: a guide to botanical nomenclature. CSIRO Publishing, Collingwood, Australia. (Also CABI International Wallingford, UK.) The definition of cultigen given in the Glossary of this reference does not include deliberately selected plants that are identical to plants growing (or once growing) in the wild. ISBN 978-0-643-09440-6 (pbk.).

Maize (pron.: /ˈmeɪz/ MAYZ; Zea mays subsp. mays L, from Spanish: maíz after Taíno mahiz), known in some English-speaking countries as corn, is a large grain plant domesticated by indigenous peoples in Mesoamerica in prehistoric times. The leafy stalk produces ears which contain the grain, which are seeds called kernels. Maize kernels are used in cooking as a starch. The Olmec and Mayans cultivated it in numerous varieties throughout Mesoamerica, cooked, ground or processed through nixtamalization. Beginning about 2500 BC, the crop spread through much of the Americas.^[1] 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 because of its ability to grow in diverse climates. Sugar-rich varieties called sweet corn are usually grown for human consumption, while field corn varieties are used for animal feed and as chemical feedstocks.

Maize is the most widely grown grain crop throughout the Americas,^[2] with 332 million metric tons grown annually in the United States alone. Approximately 40% of the crop — 130 million tons — is used for corn ethanol.^[3] Transgenic maize (genetically modified corn) made up 85% of the maize planted in the United States in 2009.^[4]

Words for maize [edit]

Many small male flowers make up the male inflorescence, called the tassel.

The word maize derives from the Spanish form of the indigenous Taíno word for the plant, maiz.^[5] It is known by other names around the world.

Corn outside the United States, Australia, and New Zealand means any cereal crop, its meaning understood to vary geographically to refer to the local staple.^[6][7] In the United States, Australia, and New Zealand,^{[citation needed]} corn primarily means maize; this usage started as a shortening of "Indian corn".^[6] "Indian corn" primarily means maize (the staple grain of indigenous Americans), but can refer more specifically to multicolored "flint corn" used for decoration.^[8]

Outside the United States, Australia, and New Zealand, the word corn often refers to maize in culinary contexts. The narrower meaning is usually indicated by some additional word, as in sweet corn, corn on the cob, popcorn, corn flakes, baby corn.

In Southern Africa, maize is commonly called mielie (Afrikaans) or mealie (English).^[9]

Maize is preferred in formal, scientific, and international usage because it refers specifically to this one grain, unlike corn, which has a complex variety of meanings that vary by context and geographic region.^[7] However, in bulk-trading, people use "corn" only to refer to maize.^{[citation needed]} Maize is used by agricultural bodies and research institutes such as the FAO and CSIRO. National agricultural and industry associations often include the word maize in their name even in English-speaking countries where the local, informal word is something other than maize; for example, the Maize Association of Australia, the Indian Maize Development Association, the Kenya Maize Consortium and Maize Breeders Network, the National Maize Association of Nigeria, the Zimbabwe Seed Maize Association.

Structure and physiology [edit]

The maize plant is often 2.5 m (meters) (8 ft) in height, though some natural strains can grow 12 m (40 ft).^[10] The stem has the appearance of a bamboo cane and is commonly composed of 20 internodes of 18 cm (7 in) length.^{[11] [12]} A leaf grows from each node, which is generally 9 cm (3.5 in) in width and 120 cm (4 ft) in length.

Ears develop above a few of the leaves in the midsection of the plant, between the stem and leaf sheath, elongating by^{[citation needed]} ~ 3 mm/day, to a length of 18 cm (7 in) (60 cm/24 in being the maximum observed in the subspecies ^[13]). They are female inflorescences, tightly enveloped by several layers of ear leaves commonly called husks. 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.

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.

Elongated stigmas, called silks, emerge from the whorl of husk leaves at the end of the ear. They are often pale yellow and 7 in (178 mm) in length, like tufts of hair in appearance. At the end of each is a carpel, which may develop into a "kernel" if fertilized by a pollen grain. The pericarp of the fruit is fused with the seed coat referred to as "caryopsis", 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 around a white, pithy substance, which forms the ear (maximum size of kernel in subspecies is reputedly 2.5 cm/1 in ^[14]). An ear commonly holds 600 kernels. 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. 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. 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.

• 

  Female inflorescence, with young silk

• 

  Stalks, ears, and silk

• 

  Male flowers

Planting density affects multiple aspects of maize. Modern farming techniques in developed countries usually rely on dense planting, which produces one ear per stalk.^[15] Stands of silage maize are yet denser,^[16] and achieve a lower percentage of ears and more plant matter.

Maize is a facultative long-night plant ^[17] and flowers in a certain number of growing degree days > 10 °C (50 °F) in the environment to which it is adapted.^[18] The magnitude of the influence that long nights have on the number of days that must pass before maize flowers is genetically prescribed^[19] and regulated by the phytochrome system.^[20] Photoperiodicity can be eccentric in tropical cultivars such that 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. These attributes, however, may prove useful in using tropical maize for biofuels.^[21]

Immature maize shoots accumulate a powerful antibiotic substance, 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA). 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.

Because of its shallow roots, maize is susceptible to droughts, intolerant of nutrient-deficient soils, and prone to be uprooted by severe winds.^[22]

• 

  Maize kernels

• 

  Maize plant diagram

• 

  Ear of maize with irregular rows of seeds

• 

  Exotic varieties of maize are collected to add genetic diversity when selectively breeding new domestic strains

• 

  Variegated maize ears

• 

  Full-grown maize plants

• 

  Zea mays "strawberry" - MHNT

Genetics [edit]

Many forms of maize are used for food, sometimes classified as various subspecies related to the amount of starch each has:

• 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 Larrañaga 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 multivariable classifications based on ever more data. Agronomic data were 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 is a diploid with 20 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 validate 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.^[23]

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, is a stock center of maize mutants. 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.^[24]

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 B73 maize genome. The resulting DNA sequence data was deposited immediately into GenBank, a public repository for genome-sequence data. Sequences and genome annotations have also been made available throughout the project's lifetime at the project's official site, MaizeSequence.org.

Primary sequencing of the maize genome was completed in 2008.^[25] On November 20, 2009, the consortium published results of its sequencing effort in Science.^[26] The genome, 85% of which is composed of transposons, was found to contain 32,540 genes (By comparison, the human genome contains about 2.9 billion bases and 26,000 genes). Much of the maize genome has been duplicated and reshuffled by helitrons - group of rolling circle transposons.^[27]

Breeding [edit]

Maize breeding in prehistory resulted in large plants producing large ears. Modern breeding began with individuals who selected highly productive varieties in their fields and then sold seed to other farmers. James L. Reid was one of the earliest and most successful developing Reid's Yellow Dent in the 1860s. These early efforts were based on mass selection. Later breeding efforts included ear to row selection, (C. G. Hopkins ca. 1896), hybrids made from selected inbred lines (G. H. Shull, 1909), and the highly successful double cross hybrids using 4 inbred lines (D. F. Jones ca. 1918, 1922). University supported breeding programs were especially important in developing and introducing modern hybrids. (Ref Jugenheimer Hybrid Maize Breeding and Seed Production pub. 1958) by the 1930s, companies such as Pioneer devoted to production of hybrid maize had begun to influence long term development. Internationally important seed banks such as CIMMYT and the U.S. bank at Maize Genetics Cooperation Stock Center University of Illinois at Urbana-Champaign maintain germplasm important for future crop development.

Genetic modification [edit]

Genetically modified (GM) maize is one of the 25 GM crops grown commercially in 2011.^[28] Grown since 1997 in the United States and Canada, 86% of the US maize crop was genetically modified in 2010^[29] and 32% of the worldwide maize crop was GM in 2011.^[30] As of 2011, Herbicide-tolerant maize varieties are grown in Argentina, Australia, Brazil, Canada, China, Colombia, El Salvador, EU, Honduras, Japan, Korea, Malaysia, Mexico, New Zealand, Philippines, the Russian Federation, Singapore, South Africa, Taiwan, Thailand, and USA, and insect-resistant corn is grown in Argentina, Australia, Brazil, Canada, Chile, China, Colombia, Czech Republic, Egypt, EU, Honduras, Japan, Korea, Malaysia, Mexico, Netherlands, New Zealand, Philippines, Romania, Russian Federation, South Africa, Switzerland, Taiwan, USA, and Uruguay.^[31]

Origin [edit]

A Tripsacum grass (big) and a teosinte (small)

Maize is the domesticated variant of teosinte.^[32] The two plants have dissimilar appearance, maize having a single tall stalk with multiple leaves and teosinte being a short, bushy plant. The difference between the two is largely controlled by differences in just two genes.^[32]

Several theories had been proposed about the specific origin of maize in Mesoamerica:^[33][34]

1. It is a direct domestication of a Mexican annual teosinte, Zea mays ssp. parviglumis, native to the Balsas River valley in south-eastern Mexico, with up to 12% of its genetic material obtained from Zea mays ssp. mexicana through introgression.
2. It has been derived 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 has undergone two or more domestications either of a wild maize or of a teosinte. (The term "teosinte" describes all species and subspecies in the genus Zea, excluding Zea mays ssp. mays.)
4. It has evolved from a hybridization of Z. diploperennis by Tripsacum dactyloides.

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. This theory about the origin of maize has been refuted by modern genetic testing, which refutes Mangelsdorf's model and the fourth listed above.^[33]:40

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

The teosinte origin theory was proposed by the Russian botanist Nikolai Ivanovich Vavilov in 1931 and the later American Nobel Prize-winner George Beadle in 1932.^[33]:10 It is supported experimentally and by recent studies of the plants' genomes. Teosinte and maize are able to cross-breed and produce fertile offspring. A number of questions remain concerning the species, among them:

1. how the immense diversity of the species of sect. Zea originated,
2. how the tiny archaeological specimens of 3500–2700 BC could have been selected from a teosinte, and
3. how domestication could have proceeded without leaving remains of teosinte or maize with teosintoid traits earlier than the earliest known until recently, dating from ca. 1100 BC.

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. Research from the 1950s to 1970s originally focused on the hypothesis that maize domestication occurred in the highlands between the states of Oaxaca and Jalisco, because the oldest archaeological remains of maize known at the time were found there. Genetic studies led by John Doebley identified Zea mays ssp. parviglumis, native to the Balsas River valley in Mexico's southwestern highlands, and also known as Balsas teosinte, as being the crop wild relative teosinte genetically most similar to modern maize.^[35] However, archaeobotanical studies published in 2009 now point to the lowlands of the Balsas River valley, where stone milling tools with maize residue have been found in a 8,700-years old layer of deposits.^[36][37][38] A primitive corn was being grown in southern Mexico, Central America, and northern South America 7,000 years ago. Archaeological remains of early maize ears, found at Guila Naquitz Cave in the Oaxaca Valley, date back roughly 6,250 years; the oldest ears from caves near Tehuacan, Puebla, date ca. 3,450 BC.^[39] Little change occurred in ear form until ca. 1100 BC when great changes appeared in ears from Mexican caves: maize diversity rapidly increased and archaeological teosinte was first deposited.

Field of maize in Liechtenstein

Corn field panorama in Aliaga, Nueva Ecija, Philippines.

Perhaps as early as 2500 BC, maize began to spread widely and rapidly. It was first cultivated in what is now the United States, at several sites in New Mexico and Arizona, about 2100 BC.^[40] 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 (along with squash, Andean region potato, quinoa, beans, and amaranth), of most 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 first millennium AD, maize cultivation spread from Mexico into the U.S. Southwest and during the following millennium into the U.S. Northeast and southeastern Canada, transforming the landscape as Native Americans cleared large forest and grassland areas for the new crop.^{[citation needed]}

Centeotl, the Aztec deity of maize

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 bivalve shell. However, George Beadle demonstrated that the kernels of teosinte are readily "popped" for human consumption, like modern popcorn. Some have argued it would have taken too many generations of selective breeding to produce large, compressed ears for efficient cultivation. However, studies of the hybrids readily made by intercrossing teosinte and modern maize suggest this objection is not well founded.

In 2005, research by the USDA Forest Service suggested that the rise in maize cultivation 500 to 1,000 years ago in what is now the southeastern United States corresponded with a decline of freshwater mussels, which are very sensitive to environmental changes.^[41]

Production [edit]

Methods [edit]

Seedlings three weeks after sowing

Young stalks

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 were "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 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 maize crop failure and consequent famine. Although it is grown mainly in wet, hot climates, it has been said to thrive in cold, hot, dry or wet conditions, meaning that it is an extremely versatile crop.^[42]

Mature plants showing ears

Maize was planted by the Native Americans in hills, in a complex system known to some as the Three Sisters. Maize provided support for beans, and the beans provided nitrogen derived from nitrogen-fixing rhizobia 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.^[43] This method was replaced by single species hill planting where each hill 60–120 cm (2.0–3.9 ft) apart was planted with three or four seeds, a method still used by home gardeners. A later technique was "checked maize", where hills were placed 40 inches (1.0 metre) 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 (3.9–4.7 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 maize fields of some Native American reservations.

A maize 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.

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.

In midwestern United States, low-till or no-till farming techniques are usually used. In low-till, fields are covered once, maybe twice, with a tillage implement either ahead of crop planting or after the previous harvest. The fields are planted and fertilized. Weeds are controlled through the use of herbicides, and no cultivation tillage is done during the growing season. This technique reduces moisture evaporation from the soil, and thus provides more moisture for the crop. The technologies mentioned in the previous paragraph enable low-till and no-till farming. Weeds compete with the crop for moisture and nutrients, making them undesirable.

Mature field maize ears

Before World War II, most maize in North America was harvested by hand. This involves a large numbers of workers and associated social events (husking or shucking bees). Some one- and two-row mechanical pickers were in use, but the maize 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 maize sheller to remove the kernels from the ear. Whole ears of maize were often stored in corn cribs, and these whole ears are a sufficient form for some livestock feeding use. Few modern farms store maize in this manner. Most harvest the grain from the field and store it in bins. The combine with a maize head (with points and snap rolls instead of a reel) does not cut the stalk; it simply pulls the stalk down. The stalk continues downward and is crumpled into a mangled pile on the ground. The ear of maize is too large to pass between slots in a plate as the snap rolls pull the stalk away, leaving only the ear and husk to enter the machinery. The combine separates out the husk and the cob, keeping only the kernels.

Quantity [edit]

Worldwide maize production

Harvesting maize during the record 2009 season in Jones County, Iowa

Maize is widely cultivated throughout the world, and a greater weight of maize is produced each year than any other grain.^{[citation needed]} 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).^[2] In 2009, over 159 million hectares (390 million acres) of maize were planted worldwide, with a yield of over 5 tonnes/hectare (80 bu/acre). Production can be significantly higher in certain regions of the world; 2009 forecasts for production in Iowa were 11614 kg/ha (185 bu/acre).^{[44][Note 1]} There is conflicting evidence to support the hypothesis that maize yield potential has increased over the past few decades. This suggests that changes in yield potential are associated with leaf angle, lodging resistance, tolerance of high plant density, disease/pest tolerance, and other agronomic traits rather than increase of yield potential per individual plant.^[45]

Top ten maize producers in 2009
Country	Production (tonnes)	Note
United States	333,010,910
China	163,118,097
Brazil	51,232,447
Mexico	20,202,600
Indonesia	17,629,740
India	17,300,000
France	15,299,900
Argentina	13,121,380
South Africa	12,050,000
Ukraine	10,486,300
World	817,110,509	[A]
No symbol = official figure, A = Aggregate (may include official, semiofficial or estimates).[2]

United States [edit]

Corn production by county in the United States, 2010

In 2010, the maize planted area for all purposes in the US was estimated at 35 million hectares (87.9 million acres),^[46] following an increasing trend since 2008.^[47] About 14% of the harvested corn area is irrigated.^[48] In 2011, corn production went down around 1% to about 13 billion bushels.^[49] The average yield in the U.S. was estimated to be 148.1 bushels per acre, making 2011 the lowest average yield since 2005.^[50] Corn production in the U.S. is expected to dramatically decline in 2012 due to widespread extreme to exceptional drought. 2012's average yield is estimated to be only 120 bushels per acre.^[51]

Pests [edit]

Insects [edit]

• Common armyworm (Pseudaletia unipuncta)
• Common earwig (Forficula auricularia)
• Corn delphacid (Peregrinus maidis)
• Corn leaf aphid (Rhopalosiphum maidis)
• Corn silkfly (Euxesta stigmatis)
• European corn borer (Ostrinia nubilalis) (ECB)
• Fall armyworm (Spodoptera frugiperda)
• Corn earworm (Helicoverpa zea)
• Lesser cornstalk borer (Elasmopalpus lignosellus)
• Maize weevil (Sitophilus zeamais)
• Southwestern corn borer (Diatraea grandiosella)
• Stalk borer (Papaipema nebris)
• Western corn rootworm (Diabrotica virgifera virgifera LeConte)

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

Diseases [edit]

• Common Rust caused by Puccinia sorghi^[52]
• 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 leaf 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

Uses [edit]

Human food [edit]

Maize being roasted over an open flame in India.

Maize and cornmeal (ground dried maize) constitute a staple food in many regions of the world.

Maize is central to Mexican food. Virtually every dish in Mexican cuisine uses maize. On form of grain or cornmeal, maize is the main ingredient of tortillas, tamales, pozole, atole and all the dishes based on them, like tacos, quesadillas, chilaquiles, enchiladas, tostadas and many more. In Mexico even a fungus of maize, known as huitlacoche is considered a delicacy.

Introduced into Africa by the Portuguese in the 16th century, maize has become Africa's most important staple food crop.^[53] Maize meal is made into a thick porridge in many cultures: from the polenta of Italy, the angu of Brazil, the mămăligă of Romania, to cornmeal mush in the U.S. (and hominy grits in the South) or the food called mealie pap in South Africa and sadza, nshima and ugali in other parts of Africa. Maize meal is also used as a replacement for wheat flour, to make cornbread and other baked products. Masa (cornmeal treated with limewater) is the main ingredient for tortillas, atole and many other dishes of Central American food.

Cut sweet white corn

Popcorn consists of kernels of certain varieties that explode when heated, forming fluffy pieces that are eaten as a snack. Roasted dried maize ears with semihardened kernels, coated with a seasoning mixture of fried chopped spring onions with salt added to the oil, is a popular snack food in Vietnam. Cancha, which are roasted maize chulpe kernels, are a very popular snack food in Peru, and also appears in traditional Peruvian ceviche. An unleavened bread called makki di roti is a popular bread eaten in the Punjab region of India and Pakistan.

Chicha and chicha morada (purple chicha) are drinks typically made from particular types of maize. The first one is fermented and alcoholic, the second is a soft drink commonly drunk in Peru. Corn flakes are a common breakfast cereal in North America and the United Kingdom, and found in many other countries all over the world.

Dried maize mote, also known as hominy, is used in Mexican cuisine

Maize can also be prepared as hominy, in which the kernels are soaked with lye in a process called nixtamalization; or grits, which are coarsely ground hominy. These are commonly eaten in the Southeastern United States, foods handed down from Native Americans, who called the dish sagamite.

The Brazilian dessert canjica is made by boiling maize kernels in sweetened milk. Maize can also be harvested and consumed in the unripe state, when the kernels are fully grown but still soft. Unripe maize must usually be cooked to become palatable; this may be done by simply boiling or roasting the whole ears and eating the kernels right off the cob. Sweet corn, a genetic variety that is high in sugars and low in starch, is usually consumed in the unripe state. Such corn on the cob is a common dish in the United States, Canada, United Kingdom, Cyprus, some parts of South America, and the Balkans, but virtually unheard of in some European countries. Corn on the cob was hawked on the streets of early 19th-century New York City by poor, barefoot "Hot Corn Girls", who were thus the precursors of hot dog carts, churro wagons, and fruit stands seen on the streets of big cities today.^[54] The cooked, unripe kernels may also be shaved off the cob and served as a vegetable in side dishes, salads, garnishes, etc. Alternatively, the raw unripe kernels may also be grated off the cobs and processed into a variety of cooked dishes, such as maize purée, tamales, pamonhas, curau, cakes, ice creams, etc.

A roadside vendor selling steamed maize in India

Maize is a major source of starch. Cornstarch (maize flour) is a major ingredient in home cooking and in many industrialized food products. Maize is also a major source of cooking oil (corn oil) and of maize gluten. Maize starch can be hydrolyzed and enzymatically treated to produce syrups, particularly high-fructose corn syrup, a sweetener; and also fermented and distilled to produce grain alcohol. Grain alcohol from maize is traditionally the source of Bourbon whiskey. Maize is sometimes used as the starch source for beer. Within the United States, the usage of maize for human consumption constitutes about 1/40th of the amount of grown in the country. In the United States and Canada, maize is mostly grown to feed for livestock, as forage, silage (made by fermentation of chopped green cornstalks), or grain. Maize meal is also a significant ingredient of some commercial animal food products, such as dog food.

Maize is also used as a fish bait, called "dough balls". It is particularly popular in Europe for coarse fishing.

Alternative medicine [edit]

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

Chemicals [edit]

Starch from maize can also be made into plastics, fabrics, adhesives, and many other chemical products.

The corn steep liquor, a plentiful watery byproduct of maize wet milling process, is widely used in the biochemical industry and research as a culture medium to grow many kinds of microorganisms.^[55]

Bio-fuel [edit]

"Feed maize" is being used increasingly for heating;^{[citation needed]} specialized corn stoves (similar to wood stoves) are available and use either feed maize or wood pellets to generate heat. Maize 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 that feeds the uniformly sized maize kernels (or wood pellets or cherry pits) into the fire.

Maize is increasingly used as a feedstock for the production of ethanol fuel.^{[citation needed]} Ethanol is mixed with gasoline to decrease the amount of pollutants emitted when used to fuel motor vehicles. High fuel prices in mid-2007 led to higher demand for ethanol, which in turn lead to higher prices paid to farmers for maize. This led to the 2007 harvest being one of the most profitable maize crops in modern history for farmers. Because of the relationship between fuel and maize, prices paid for the crop now tend to track the price of oil.^{[citation needed]}

The price of food is affected to a certain degree by the use of maize for biofuel production. The cost of transportation, production, and marketing are a large portion (80%) of the price of food in the United States. Higher energy costs affect these costs, especially transportation. The increase in food prices the consumer has been seeing is mainly due to the higher energy cost. The effect of biofuel production on other food crop prices is indirect. Use of maize for biofuel production increases the demand, and therefore price of maize. This, in turn, results in farm acreage being diverted from other food crops to maize production. This reduces the supply of the other food crops and increases their prices.^[56][57]

Farm-based maize silage digester located near Neumünster in Germany, 2007. Green inflatable biogas holder is shown on top of the digester

Maize is widely used in Germany as a feedstock for biogas plants. Here the maize is harvested, shredded then placed in silage clamps from which it is fed into the biogas plants. This process makes use of the whole plant rather than simply using the kernels as in the production of fuel ethanol.

A biomass gasification power plant in Strem near Güssing, Burgenland, Austria, began in 2005. Research is being done to make diesel out of the biogas by the Fischer Tropsch method.

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 (what is nowadays also known as "biofuels" and has been generating an intense debate regarding the human beings' necessity of new sources of energy, on the one hand, and the need to maintain, in regions such as Latin America, the food habits and culture which has been the essence of civilizations such as the one originated in Mesoamerica; the entry, January 2008, of maize among the commercial agreements of NAFTA has increased this debate, considering the bad labor conditions of workers in the fields, and mainly the fact that NAFTA "opened the doors to the import of maize from the United States, where the farmers who grow it receive multimillion dollar subsidies and other government supports. (...) According to OXFAM UK, after NAFTA went into effect, the price of maize in Mexico fell 70% between 1994 and 2001. The number of farm jobs dropped as well: from 8.1 million in 1993 to 6.8 million in 2002. Many of those who found themselves without work were small-scale maize growers.").^[58] However, introduction in the northern latitudes of the U.S. of tropical maize for biofuels, and not for human or animal consumption, may potentially alleviate this.

As a result of the U.S. federal government announcing its production target of 35 billion US gallons (130,000,000 m³) of biofuels by 2017, ethanol production will grow to 7 billion US gallons (26,000,000 m³) by 2010, up from 4.5 billion in 2006, boosting ethanol's share of maize demand in the U.S. from 22.6 percent to 36.1 percent.^[59]

Ornamental and other uses [edit]

Some forms of the plant are occasionally grown for ornamental use in the garden. For this purpose, variegated and colored leaf forms as well as those with colorful ears are used.

Corncobs can be hollowed out and treated to make inexpensive smoking pipes, first manufactured in the United States in 1869.

Children playing in a maize kernel box

An unusual use for maize is to create a "corn maze" (or "maize maze") as a tourist attraction. The idea of a maize maze was introduced by the American Maze Company who created a maze in Pennsylvania in 1993.^[60] 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 popular in many farming communities.

Maize kernels can be used in place of sand in a sandboxlike enclosure for children's play.^[61]

Additionally, feed corn is sometimes used by hunters to bait animals such as deer or wild hogs.

Fodder [edit]

Maize makes a greater quantity of epigeous mass than other cereal plants, so can be used for fodder. Digestibility and palatability are higher when ensiled and fermented, rather than dried.

Commodity [edit]

Maize is bought and sold by investors and price speculators as a tradable commodity using corn futures contracts. These "futures" are traded on the Chicago Board of Trade (CBOT) under ticker symbol C. They are delivered every year in March, May, July, September, and December.^[62]

U.S. usage breakdown [edit]

The breakdown of usage of the 12.1 billion bushel 2008 U.S. maize crop was as follows, according to the World Agricultural Supply and Demand Estimates Report by the USDA.^[63]

• 5,250 million bu. - livestock feed
• 3,650 million bu. - ethanol production
• 1,850 million bu. - exports
• 943 million bu. - production of starch, corn oil, sweeteners (HFCS, etc.)
• 327 million bu. - human consumption - grits, corn flour, corn meal, beverage alcohol

Comparison to other staple foods [edit]

The following table shows the nutrient content of maize and major staple foods in a raw harvested form. Raw forms are not edible and cannot be digested. These must be sprouted, or prepared and cooked for human consumption. In sprouted or cooked form, the relative nutritional and anti-nutritional contents of each of these staples are different from that of raw form of these staples reported in the table below.

Hazards [edit]

Pellagra [edit]

This section needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (July 2010)

When maize was first introduced into farming systems other than those used by traditional native-American peoples, it was generally welcomed with enthusiasm for its productivity. However, a widespread problem of malnutrition soon arose wherever maize was introduced as a staple food. This was a mystery, since these types of malnutrition were not normally seen among the indigenous Americans, for whom maize was the principal staple food.^[65]

It was eventually discovered that the indigenous Americans had learned to soak maize^{[citation needed]} in alkali-water—made with ashes and lime (calcium oxide) by Mesoamericans and North Americans—which liberates 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 availability of lysine and tryptophan to some extent, but more importantly, the indigenous Americans had also learned to balance their consumption of maize with beans and other protein sources such as amaranth and chia, as well as meat and fish, to acquire the complete range of amino acids for normal protein synthesis.

Maize was introduced into the diet of nonindigenous Americans without the necessary cultural knowledge acquired over thousands of years in the Americas. In the late 19th century, pellagra reached epidemic proportions in parts of the southern U.S., as medical researchers debated two theories for its origin: the deficiency theory (which was eventually shown to be true) said that pellagra was due to a deficiency of some nutrient, and the germ theory said that pellagra was caused by a germ transmitted by stable flies. A third theory, promoted by the eugenicist Charles Davenport, held that people only contracted pellagra were susceptible to it due to certain “constitutional, inheritable” traits of the affected individual.^[66] In 1914, the U.S. government officially endorsed the germ theory of pellagra, but rescinded this endorsement several years later when the evidence grew against it. By the mid-1920s, the deficiency theory of pellagra was becoming scientific consensus, and the theory was validated in 1932 when niacin deficiency was determined to be the cause of the illness.

Once alkali processing and dietary variety were understood and applied, pellagra disappeared in the developed world. The development of high lysine maize and the promotion of a more balanced diet have also contributed to its demise. Pellagra still exists today in food-poor areas and refugee camps where people survive on donated maize.^[67]

Allergy [edit]

Maize contains lipid transfer protein, an indigestible protein that survives cooking. This protein has been linked to a rare and understudied allergy to maize in humans.^[68] The allergic reaction can cause skin rash, swelling or itching of mucous membranes, diarrhea, vomiting, asthma and, in severe cases, anaphylaxis. It is unclear how common this allergy is in the general population.

Art [edit]

Gold maize. Moche culture 300 A.D., Larco Museum, Lima, Peru

Water tower in Rochester, Minnesota being painted as an ear of maize

Maize has been an essential crop in the Andes since the pre-Columbian Era. The Moche culture from Northern Peru made ceramics from earth, water, and fire. This pottery was a sacred substance, formed in significant shapes and used to represent important themes. Maize represented anthropomorphically as well as naturally.^[69]

In the United States, maize ears along with tobacco leaves are carved into the capitals of columns in the U.S. Capitol building. Maize itself is sometimes used for temporary architectural detailing when the intent is to celebrate the fall season, local agricultural productivity and culture. Bundles of dried maize stalks are often displayed often along with pumpkins, gourds and straw in autumnal displays outside homes and businesses. A well-known example of architectural use is the Corn Palace in Mitchell, South Dakota, which uses cobs and ears of colored maize to implement a mural design that is recycled annually.

A maize stalk with two ripe ears is depicted on the reverse of the Croatian 1 lipa coin, minted since 1993.^[70]

See also [edit]

Notes [edit]

References [edit]

• Aureliano Brandolni, Andrea Brandolini. Il mais in Italia: storia naturale e agricola XII+370 pages and 80 colour pages. CRF press. Bergamo, Italy, 2006.
• Ferro, D.N. and Weber, D.C. Managing Sweet Corn Pests in Massachusetts

Popped popcorn

Popcorn, also known as popping corn, is a type of corn (maize, Zea mays var. everta) that expands from the kernel and puffs up when heated. Corn is able to pop because, like amaranth grain, sorghum, quinoa and millet, its kernels have a hard moisture-sealed hull and a dense starchy interior. This allows pressure to build inside the kernel until an explosive "pop" results. Some strains of corn are now cultivated specifically as popping corns.

There are many techniques for popping corn. Commercial large-scale popcorn machines were invented by Charles Cretors in the late 19th century. Many types of small-scale home methods for popping corn also exist, along with prepackaged popcorn.

Depending on how it is prepared and cooked, some consider it to be a health food while others caution against it for a variety of reasons. Popcorn can also have non-food applications, ranging from holiday decorations to packaging materials.

History [edit]

Popcorn on the cob before shelling

Popcorn was first discovered thousands of years ago by the Guatemalans. It is one of the oldest forms of corn: evidence of popcorn from 3600 BCE was found in New Mexico and even earlier evidence dating to perhaps as early as 4700 BCE was found in Peru. Some popcorn has been found in early 1900s to be a purple color.^[1][2]

The English who came to America in the 16th and 17th centuries learned about popcorn from the Native Americans.

During the Great Depression, popcorn was comparatively cheap at 5–10 cents a bag and became popular. Thus, while other businesses failed, the popcorn business thrived and became a source of income for many struggling farmers. During World War II, sugar rations diminished candy production, causing Americans to eat three times as much popcorn as they had before.^[3]

At least six localities (all in the Midwestern United States) claim to be the "Popcorn Capital of the World": Ridgway, Illinois; Valparaiso, Indiana; Van Buren, Indiana; Schaller, Iowa; Marion, Ohio; and North Loup, Nebraska. According to the USDA, most of the corn used for popcorn production is specifically planted for this purpose; most is grown in Nebraska and Indiana, with increasing area in Texas.^[4][5]

As the result of an elementary school project, popcorn became the official state snack food of Illinois.^[6]

Popping mechanism [edit]

The process of a kernel popping

Each kernel of popcorn contains a certain amount of moisture and oil. Unlike most other grains, the outer hull of the popcorn kernel is both strong and impervious to moisture, and the starch inside consists almost entirely of a hard, dense type.^[7]

As the oil and the water around the kernel are heated, they turn the moisture in the kernel, which has a moisture-proof hull, into a superheated pressurized steam. Under these conditions, the starch inside the kernel gelatinizes, softens and becomes pliable. The pressure continues to increase until the breaking point of the hull is reached: a pressure of about 135 psi (930 kPa)^[7] and a temperature of 180 °C (356 °F). The hull ruptures rapidly, causing a sudden drop in pressure inside the kernel and a corresponding rapid expansion of the steam, which expands the starch and proteins of the endosperm into airy foam. As the foam rapidly cools, the starch and protein polymers set into the familiar crispy puff.^[7] Special varieties are grown to give improved popping yield. Some wild types will pop, but the cultivated strain is Zea mays everta, which is a special kind of flint corn.

Cooking methods [edit]

An early popcorn machine in a street cart, invented in the 1880s by Charles Cretors in Chicago

Although small quantities can be popped in a stove-top kettle, or pot in a home kitchen, commercial sale of freshly popped popcorn employs specially designed popcorn machines, which were invented in Chicago, Illinois, by Charles Cretors in 1885. Cretors successfully introduced his invention at the Columbian Exposition in 1893. At this same world's fair, F.W. Rueckheim introduced a molasses-flavored "Candied Popcorn", the first caramel corn; his brother, Louis, slightly altered the recipe and introduced it as Cracker Jack popcorn in 1896.^[8]

Cretors's invention introduced the first patented steam-driven popcorn machine that popped corn in oil. Previously, vendors popped corn by holding a wire basket over an open flame. At best, the result was a hot, dry, unevenly cooked snack. Cretors's machine popped corn in a mixture of one-third clarified butter, two-thirds lard, and salt. This mixture could withstand the 450 °F (232 °C) temperature needed to pop corn and it produced little smoke. A fire under a boiler created steam that drove a small engine; that engine drove the gears, shaft, and agitator that stirred the corn and powered a small automated clown puppet-like figure, "the Toasty Roasty Man", an attention attracting amusement intended to drum up business. A wire connected to the top of the cooking pan allowed the operator to disengage the drive mechanism, lift the cover, and dump popped corn into the storage bin beneath. Exhaust from the steam engine was piped to a hollow pan below the corn storage bin and kept freshly popped corn uniformly warm for the first time. Excess steam was also used to operate a small, shrill whistle to further attract attention.^[9]

An in-home hot-air popcorn maker

A very different method of popcorn-making can still be seen on the streets of some Chinese cities today. The un-popped corn kernels are poured into a large cast-iron canister — sometimes called a 'popcorn hammer' — that is then sealed with a heavy lid and slowly turned over a curbside fire in rotisserie fashion. When a pressure gauge on the canister reaches a certain level, the canister is removed from the fire, a large canvas sack is put over the lid, and the seal is released. With a huge boom, all of the popcorn explodes at once and is poured into the sack.^[10][11][12] This method is believed to have been developed during the Song dynasty originally for puffing rice.

Individual consumers can also buy and use specialized popping appliances that typically generate no more than a gallon of popped corn per batch. Some of these appliances also accept a small volume of oil or melted butter to assist thermal transfer from a stationary heating element, but others are "air poppers" which rapidly circulate heated air up through the interior, keeping the un-popped kernels in motion to avoid burning and then blowing the popped kernels out through the chute. The majority of popcorn sold for home consumption is now packaged in a microwave popcorn bag for use in a microwave oven.^[13]

Expansion and yield [edit]

Popping results are sensitive to the rate at which the kernels are heated. If heated too quickly, the steam in the outer layers of the kernel can reach high pressures and rupture the hull before the starch in the center of the kernel can fully gelatinize, leading to partially popped kernels with hard centers. Heating too slowly leads to entirely unpopped kernels: the tip of the kernel, where it attached to the cob, is not entirely moisture-proof, and when heated slowly, the steam can leak out of the tip fast enough to keep the pressure from rising sufficiently to break the hull and cause the pop.^[14]

Producers and sellers of popcorn consider two major factors in evaluating the quality of popcorn: what percentage of the kernels will pop, and how much each popped kernel expands. Expansion is an important factor to both the consumer and vendor. For the consumer, larger pieces of popcorn tend to be more tender and are associated with higher quality. For the grower, distributor, and vendor, expansion is closely correlated with profit: vendors such as theaters buy popcorn by weight and sell it by volume. For both these reasons, higher-expansion popcorn fetches a higher profit per unit weight.

Popcorn will pop when freshly harvested, but not well: its high moisture content leads to poor expansion and chewy pieces of popcorn. Kernels with a high moisture content are also susceptible to mold when stored. For these reasons, popcorn growers and distributors dry the kernels until they reach the moisture level at which they expand the most. This differs by variety and conditions, but is generally in the range of 14–15% moisture by weight. If the kernels are over-dried, the expansion rate will suffer and the percentage of kernels that pop at all will decline.

Two explanations exist for kernels which do not pop at proper temperatures, known in the popcorn industry as "old maids"^{[citation needed]}. The first is that unpopped kernels do not have enough moisture to create enough steam for an explosion. The second explanation, according to research led by Dr. Bruce Hamaker of Purdue University, is that the unpopped kernel may have a leaky hull.

Popcorn varieties are broadly categorized by the shape of the kernels, the color of the kernels, or the shape of the popped corn. While the kernels may come in a variety of colors, the popped corn is always off-yellow or white as it is only the hull (or pericarp) that is colored. "Rice" type popcorns have a long kernel pointed at both ends; "pearl" type kernels are rounded at the top. Commercial popcorn production has moved mostly to pearl types.^[15] Historically, pearl popcorns were usually yellow and rice popcorns usually white. Today both shapes are available in both colors, as well as others including black, red, and variegated. Commercial production is dominated by white and yellow.^[16]

"Mushroom"-shaped popcorn, left, is less fragile and less tender than "butterfly"-shaped, right

Jargon [edit]

In popcorn jargon, a popped kernel of corn is known as a "flake". Two shapes of flakes are commercially important. "Butterfly" flakes are irregular in shape and have a number of protruding "wings". "Mushroom" flakes are largely ball-shaped, with few wings. Butterfly flakes are regarded as having better mouthfeel, with greater tenderness and less noticeable hulls. Mushroom flakes are less fragile than butterfly flakes and are therefore often used for packaged popcorn or confectionery, such as caramel corn.^[16] The kernels from a single cob of popcorn may form both butterfly and mushroom flakes; hybrids that produce 100% butterfly flakes or 100% mushroom flakes exist, the latter developed only as recently as 1998.^[16] Growing conditions and popping environment can also affect the butterfly-to-mushroom ratio.

Consumption [edit]

Popcorn is commonly eaten in movie theaters. This snack is usually served salted or sweetened. In North America, it is traditionally served salted, often with butter or a butterlike topping. However, sweetened versions, such as caramel corn and kettle corn, are also commonly available. In the United Kingdom, ready-made popcorn is available either salted or simply sweetened with sugar. Toffee (i.e. caramel) popcorn is also available, but tends to be more expensive. In Peru popcorn is sometimes sweetened with small candy pellets and sweetened condensed milk, but its more often eaten with salt and the only buttered version known to any considerable degree is the microwave popcorn. Popcorn is a popular snack food at sporting events and in cinemas, where it has been served since 1914.^{[citation needed]}

Popcorn as a breakfast cereal was consumed by Americans in the 1800s, and generally consisted of popcorn with milk and a sweetener.^[17]

Nutritional value [edit]

Air-popped popcorn is naturally high in dietary fiber, low in calories and fat, and free of sugar and sodium.^[18] This can make it an attractive snack to people with dietary restrictions on the intake of calories, fat, and/or sodium. For the sake of flavor, however, large amounts of fat, sugar, and sodium are often added to prepared popcorn, which can quickly convert it to a very poor choice for those on restricted diets.

One particularly notorious example of this first came to public attention in the mid-1990s, when the Center for Science in the Public Interest produced a report about "Movie Popcorn", which became the subject of a widespread publicity campaign. The movie theaters surveyed used coconut oil to pop the corn, and then topped it with butter or margarine. "A medium-size buttered popcorn", the report said, "contains more fat than a breakfast of bacon and eggs, a Big Mac and fries, and a steak dinner combined."^[19] The practice continues today. For example, according to DietFacts.com, a small popcorn from Regal Cinema Group (the largest theater chain in the United States)^[20] still contains 29 g of saturated fat,^[21] as much as three Big Macs^[22] and the equivalent of a full day-and-a-half's reference daily intake.^[23]

Health risks [edit]

Popcorn is included on the list of foods that the American Academy of Pediatrics recommends not serving to children under four, because of the risk of choking.^[24]

Microwaveable popcorn represents a special case, since it is designed to be cooked along with its various flavoring agents. One of these common artificial-butter flavorants, diacetyl, has been implicated in causing respiratory ailments.^[25]

Other uses [edit]

Popcorn, threaded onto a string, is used as a wall or Christmas tree decoration in some parts of North America,^[26][27] as well as on the Balkan peninsula.^[28]

Some shipping companies have experimented with using popcorn as a biodegradable replacement for expanded polystyrene packing material. However, popcorn has numerous undesirable properties as a packing material, including attractiveness to pests, flammability, and a higher cost and greater density than expanded polystyrene. A more processed form of expanded corn foam has been developed to overcome some of these limitations.^[29]

The world's largest popcorn ball was unveiled in October 2006 in Lake Forest, Illinois. It weighed 3,415 pounds (1,549 kg), measured 8 feet (2.4 m) in diameter, and had a circumference of 24.6 ft (7.5 m).^[30]

See also [edit]

• Butter salt
• Popcorn maker
• Puffed grain

References [edit]

Additional reading [edit]

• Hallauer, Arnel R. (2001). Specialty Corns. CRC Press. ISBN 0-8493-2377-0. 
• Lusas, Edmund W.; Rooney, Lloyd W. (2001). Snack Foods Processing. CRC press. ISBN 1-56676-932-9. 
• Smith, Andrew F. (1999). Popped Culture: The Social History of Popcorn in America. University of South Carolina Press. ISBN 1-57003-300-5.