The waxy corn is a Maïs Hybride whose Amidon of the grain entirely consists of Amylopectine and who presents an private interest for certain industrial preparations.

The waxy corn was discovered in China in 1909. As this plant had various characteristics, the American selectors used it a long time like genetic Marqueur in order to make visible certain genes hidden in other programmes of selection of the Maïs. In 1922, a researcher found that the Endosperme waxy corn contained only amylopectin and not Amylose contrary to the conventional varieties of toothed corn which contains both. Until the Second world war the independent source of amylopectin was the Manioc but when the Japanese cut the lines of provisioning of the United States, American industry had to turn to waxy corn.

The amylopectin is used in the food products, textiles, adhesives like in the industry of paper and corrugated cardboard. Shortly after the war, of the tests showed that the af Fourrage lies containing waxy corn allows a fattening faster than the toothed corn allows it. The waxy corn then knew a sharp profit of interest. The geneticists could show that this corn has a deficiency in the Métabolisme preventing the amylose synthesis in the endosperme. It is coded by a single gene (wx). The waxy corn gives an output of 3,5% lower than his congeneric toothed and must be planted with at least two hundred meters of conventional corn fields under risk of contamination.

History

The waxy corn is mentioned for the first time in the files of the American ministry of agriculture (USDA), but the exact history of this variety of corn is unknown. In 1908, the father J. Mr. W. Farnham, missionary presbytérien with Shanghai, off sent a seed sample to U.S. Office Foreign Seed and Plant Introduction . An annexed note presented it as follows: “ Standard corn private individual. There are several colors, but it is said that they all are of the same variety. The grain is, seems it, much more viscous to me than in the other varieties and can be appropriate for certain uses, perhaps out of pulp. ”. These seeds were sown the May 9th 1908, close to Washington, D.C, by a Botaniste of the name of G.N. Hakes. It succeeds in leading 53 seedlings to maturity and made of it a detailed description, accompanied by photographs, which was published in a bulletin of the USDA published in December 1909. In 1915, the plant was redécouverte in High-Burma and again into 1920 with the Filipino . Kuleshov, when it checked the distribution of corn in Asia, found it in many other places.

The discovery in China of a type of distinct corn raised the historical question to know if the corn were known in the Far East before the discovery of America. The controversy was closed at the end of the XIXe century by De Candolle which declared that: “the corn is of American origin, and was introduced into the old world only since the discovery of new. I regard these two assertions as positive, in spite of the contrary opinion of some authors”. But the discovery of this single variety of corn suggested a re-examination of the question. It also stated that the Portuguese arrived to China in 1516, there introducing corn simultaneously.

Hakes put forth the assumption that the waxy corn appeared following a Mutation in High-Burma. On this assumption, it seemed difficult to conceive that since 1516 this American plant time had to penetrate in a wild country inaccessible the abroads, to produce a change, and then, as a mutant to spread itself from Philippines until the north of Mandchourie and with the area of Primorsky in the space of three or four hundred years. One can answer these two arguments today. Initially, it is known that the change waxy is very common (see #Genetic). Then, the fact that the corn, even introduced in Asia after the time of Christophe Colomb, had to be quickly accepted by the late populations states only that, following the example potato in Ireland, it met an acute and pressing need. According to Goodrich there exists in China some 6000 local stories written since 347. The first description specifies corn in these publications dates from XVIe century.

Ho, eminent Chinese historian, indicated: “ in short of the introduction of corn in China, we can say that the corn was introduced in China two or three decades before 1550… ” It could be that, as certain studies affirm it, the corn arrived to Asia before 1492, but at present not only one fragment of plant, nor no object, no illustration or traces written, was not brought to our attention to prove it. Consequently, any not documented assertion that this event it would be produced at one former time must be considered with skepticism until it is proven. Thus, the two assertions of Candolle remain valid.

In its publication, Collins characterized this new plant by the possession of many single natures. No trace of these characters in the recorded forms of Zea mays had hitherto been found. The combination of several of these characters confers on the plant a resistance to the drying of silks by the dry and hot winds at the time of flowering. Although these plants produce of so small ears which they could not enter in direct competition with the improved varieties, the presence of this adaptation gave them an economic interest, particularly in certain semi-arid areas of the South-west of the United States. One thus sought to introduce by hybridization the desirable characters of this small variety into the types of larger and more productive corn.

When Collins discovered such a difference in aspect of the endosperme between a waxy corn and a normal type, he suspected a difference in the chemical composition, but the analyzes did not show any unusual result. The percentages of starch, oil and proteins were all in the usual standards. However the physical nature of the starch intrigued it and he wrote: “ Within sight of the recent development of corn products specialized for the human consumption, the single type of starch can have a certain economic importance ”.

In fact, during many years the principal use of waxy corn was that of genetic marker for other programmes of corn selection. The selectors were able to use certain characters “to label” the existence of hidden genes and to follow them in the programs of selection. The waxy corn could disparaïre again in the United States without this particular application in the selection.

In 1922, another researcher, P. Weatherwax of the university of Indiana with Bloomington, announced that the starch of waxy corn was entirely of a “rare” form called “érythrodextrine”, known today under the name of Amylopectine. He discovered that this rare starch was tinted in red in the presence of Iode, whereas the normal starch is dyed in blue. Packsaddlled, French and Al and Sprague, Brimhall, and Al confirmed that the starch of the endosperme waxy corn is made up almost exclusively of amylopectin. The presence of amylopectin in rice had been shown previously by Parnell.

In 1937, right before the Second world war, G.F. Sprague and other selectors of what was then the Iowa State College had undertaken a program of crossings to try to introduce the waxy character into a high-output hybrid corn. At that time, the waxy type did not refer any more particular structural noted by Collins, probably because of the years of hybridizations with varied genetic stocks. Only, the single endosperme had been preserved.

The waxy corn then did not have a very great importance because the primary source of pure amylopectin was still the Manioc, shrub tropical with large underground tuber. This situation will perdura until the Second world war, when the Japanese cut the lines of provisioning of the United States and forced the transformers to turn to waxy corn. This last then appeared particularly adapted to this objective because it could be ground with the same equipment already largely used for ordinary corn.

According to H.H. Schopmeyer the production of waxy corn in Iowa at industrial ends rose with 356 tons in 1942 and 2540 tons in 1943. In 1944, there existed only five varieties of waxy corn suited to the production of waxy starch. In 1943, to meet all the requirements out of amylopectin, approximately 81.650 tons of grains were produced. Since the Second world war until 1971, all the waxy corn produces in the United States was it within the framework of contracts with transformers for industry or the food sector. In fact, the essence of this corn was cultivated in a small number of counties of the States of the Iowa, Illinois and Indiana. But in 1970, an epidemic of Helminthosporiose of the corn ( Helminthosporium maydis Nisik. and Miyake) prevails in all the American Corn Belt .

At the same time, at least 80% of corn cultivated in the United States were sensitive to the helminthosporiose because this corn contained a male-sterile cytoplasm of the “Texas type”, which allowed the production of hybrid seeds without it being necessary to proceed to mechanical or manual castration. Also quite naturally, there was a true panic in 1971 to find a type of corn to the normal cytoplasm - cytoplasm resistant to the helminthosporiose. Thus waxy corn seeds entered the market.

Rétrocroisements were also carried out largely to transfer from particular genes such as wx ( waxy ), O2 and gene HT of resistance to the helminthopsoriose. Certain farmers who fed to them bovine Bétail with waxy corn grains noticed that the animals profited better. Tests of food were organized which showed that the waxy corn involved better profits of weight that the toothed normal corn. The interest for waxy corn exploded suddenly, and this type of corn lost its statute of botanical curiosity and production specialized to become the object of research of the greattest importance. In 2002, a production estimated between 1,2 and 1,3 million tons was carried out in the United States on approximately 2.000 km ², accounting for only 0,5% of the American total production of corn.

Biology

Chinese corn

Hakes noted, inter alia, the characters following, unusual, of Chinese corn:

• several single structural features which make it possible the plants to resist the drying of silks by the wind at the stage of flowering;
• a particular port, in the sense that the four or five higher sheets appear all on the same side of the principal stem of the plant; the sheets of the higher nodes are very set up, whereas the low sheets are spread out and falling down;
• one of the principal things which it noted is the composition of the endosperme corn grains; on this subject he wrote:

“ the texture of the endosperme is one of the single features of this corn. Crossed according to any direction, it separates while following a kind of cleavage, exposing a dull and smooth surface; texture evokes that of the hardest waxes, although it is even harder and more crystalline. It is this optical resemblance which suggested the term of waxy endosperme. ”

The water content of the grain must be with most equal to 16% so that the waxy character can be recognized visually. The starch of toothed normal corn is characterized by a content from approximately amylose 25%, the remainder being the amamylopectine and the intermediate fraction (see 3.5 Biochemistry). But these percentages vary according to the cultivars and according to the development of the grain. For example, the percentage of amylose goes from 20 to 36% per 399 normal corn cultivars. There exist sources of germinatif corn plasma which goes from less than 20% to 100% of amylopectin complement.

It is of great interest because the fractionation of the normal starch to obtain amylose or amylopectin pure is very expensive. The waxy endosperme is in oneself a defect of the metabolism, and its weak frequency at the majority of the corn populations vis-a-vis recurring changes indicates that it is expressed against the natural selection.

Derives genetic

Experiments undertaken by Sprague showed that ten to twenty plants are necessary to have an adequate representation of genetic diversity in a variety of corn to open pollination. As the number of preserved ears as seed by the former Asian farmers who did not lay out that small squares of ground was often lower and, in fact, considering new corn populations are sometimes created by sowing the descent of only one ear, it follows that it had to often occur a genetic Dérive in the frequency of genes resulting from the creation of small settlements of selection.

A genetic striking example of drift at corn is the occurrence in certain parts of Asia of varieties to waxy endosperme. Such varieties are unknown at American corn, but the waxy character was discovered to him at nonwaxy varieties: at a corn flint of New England and at a South American variety.

The fact that the waxy corn is so commonly in a part of the world who has also waxy varieties of rice, of sorghum and of millet can be allotted to an artificial selection. The inhabitants of Asia being familiar of the waxy varieties of these cereals and accustomed to use them for particular uses recognized the waxy character of corn following its introduction in Asia after the discovery of America and deliberately isolated from the varieties purely for their waxy endosperme. But the fact that the waxy endosperme drew their attention the first time is probably due to the genetic drift. The gene of the waxy endosperme, which has a low frequency at American corn, apparently reached a frequency raised in certain Asian corn samples.

In fact, the practice reported by Stonor and Anderson to cultivate corn in the form of plants isolated among other cereals had to involve a certain share of autopollinisation and, in any stock in which the waxy gene was present, was to inevitably lead in a very short amount of time with the establishment of pure varieties of waxy corn to the special properties that the people accustomed to the waxy characters of other cereals could with difficulty miss recognizing

Genetics

A single Recessive gene waxy (wx), located on the shortest arm of chromosome 9, code the Endosperme waxy of the corn grain (the Wx allele codes a endosperme with normal starch). This fact was shown in first by Collins and Kempton. The structure of the locus of the wild waxy type (wx+) was determined by analyzes sequential DNA. The gene has 3718 even bases (14 Exon S and 13 Intron S). The waxy endosperme is the equivalent for corn of the sticky character “” at the Riz. Many other species present also this “waxy” Mutation, among which, in addition to rice, the Sorgho, millet, barley and the corn. It is always characterized by the blue coloring of the starch granules in the presence of iodine.

At the time of crossings between plants Hétérozygote S for the waxy character, one notes small, but significant, variation compared to the ratio mendélien awaited in Bear car-pollination obtained, starting from 71 ségrégués ears of the generation F1, 23,77% of waxy grains and 76,23% nonwaxy grains. That is highlighted by the two hétérozygotes types, Wx Wx wx and wx wx Wx. The gene waxy is epistatic for all other known mutant genes forming starch such as dull (of), sugary-1 (su1) and sugary-2 (su2), it increases sugars and the water soluble Polysaccharide S with su1 and it causes a spectacular increase in sugars and a reduction of the starch with ae or ae of. The change of Wx with wx is not rare at the varieties cultivated in the Corn Belt , Bear having found three changes separated in wx in three consecutive years in a total population from some 100.000 ears.

Mangelsdorf also discovered many mutants in its experimental plots. Waxy allele the “of Argentina” (wx-a) of the locus waxy announced initially by Andrés and Bascialli, is known to produce an minor amount of amylose (< 5%) and gives an intermediate coloring with iodine. Other mutant alleles of the locus waxy were announced, which have starches with the properties similar to those observed with the allele wx. One knows more than 40 Allèle S mutants for the Locus waxy , which makes of it the most beautiful whole of changes found at the higher plants. Some of them are very stable then of others are very unstable.

The Phénotype of the stable mutants remains unchanged while that of the unstable mutants changes because of insertion of elements transposable (5-8) is highly recommended. Owing to the fact that the change waxy is expressed by a nonlethal and easily identifiable phenotype, it was the subject of important research during the XXe century. Nelson carried out a detailed chart of the genetic structure of the majority of these changes.

Genotype and characterization with iodine

The locus wx is expressed in the endosperme, in the male Gamétophyte (Pollen) like in the gamétophyte female (embryonic Sac). The amylose and the amylopectin have properties of fixing of the different Iode, amylose and corn amylopectin giving of the values of affinity for the iodine of approximately 19 to 20 and 1%, respectively. Weatherwax discovered this reaction in 1922.

The quantity of apparent amylose can be given is by measuring the Absorbance complex starch-iodine and by bringing back this value to the reference of pure amylose or amylopectin or by measuring the quantity of iodine (Mg) fixed for 100 starch Mg by a potentiometric Titrage and by comparing the value found with the quantity fixed by a standard amylose. The values used for the fixing of iodine, however, are only estimates of the amylose contents because of the differences in the capacity of fixing (and the structure) of amylose and amylopectin according to the types of starch. For example, the amylopectin molecules with long external branches fix more iodine than those at short branches, from where a weak measurement of apparent amylose. The chromatographic profiles starch of the wx type, however, do not reveal any amylose peak.

The seedlings Hétérozygote S for the gene waxy (Wx: wx) can be characterized by treating pollen with iodine. The half of pollen will be blue and the other brown half while the grains will remain blue (very useful in the programs of rétrocroisement). If the plant is homozygote recessive (wx: wx), all pollen will be brown and the grains too. At the dominant homozygotes (Wx: Wx), iodine will become blue.

Agronomic aspects

The culture of the corn whose starch consists of pure amylopectin is not simple. The gene waxy being recessive, the waxy corn must be isolated from at least 200 meters of any normal corn field. However, in the monoculture of corn, natural sowings are not rare in the areas without freezing, but some push back in a waxy corn field are enough to contaminate all the field even if it is insulated. A solution could be to make from the 15 to 20 lines external of the field a band plug, which can be used to nourish the cattle. The need for detecting any contamination by normal corn would justify the creation of waxy varieties to white grains, which would allow the sorting of the grains by electric eyes and the rejection of the contaminated seeds. But this idea did not have a known application.

The response to fertilizers, the diseases, the devastating insects, the environmental stresses, etc, should not in theory mark any difference between the hybrids of waxy corn and its equivalents toothed owing to the fact that no difference exists between these two types of corn, except in the grain. The sucrose is the sugar of transport, but it is normally converted into starch when it is transferred in the endosperme from corn.

Use

The amylopectin: industrial uses

The starch is the main thing carbohydrate of reserve in the vegetable kingdom. Although this substance is present at the majority of the plant species, only some are used for the commercial production of starch, and the corn is the independent source of the starch produced industrially in the world. With the second rank, the potato, followed is corn and, to a lesser extent, rice. The corn starch was produced for the first time in the United States in 1844 in the factory of William Colgate to Jersey City (New Jersey).

The amylopectin yield of the corn grain goes from 58,5 to 69% (of the matter dries). The wet waxy corn grinding gives outputs from only 90% compared to those of toothed corn. The starch wx is relatively easy to gelatinize and produces a clear viscous paste on the sticking and poisseuse surface which resembles those produced by the starches of roots or tubers, such as potato and Tapioca. The majority of the starches in their or not modified natural form have the employment limited in various industries. Therefore, majority of the starches of which the waxy corn starches are modified either to improve their intrinsic properties, or for the repress, according to the needs required by the particular applications. Many types of modified waxy starches have a multitude of applications in industries of paper, the textile, corrugated cardboard, and the adhesives without counting the enormous range of the applications in the Agro-alimentaire.

Food products

The modified waxy corn starches have important applications in the food field, in particular the improvement of the uniformity, the stability and the texture of various food products. The limpidity and the stability of the amylopectin starch in fact a product particularly adapted like thickener for fruit tarts. It improves the consistency and the crémeux one of the Conserve S and the dairy products as well as resistance to the congelation-defrosting of the frozen products. It gives a more pleasant texture and an aspect to dry food and the mixtures.

Textile industry

The waxy starch is of an interest for textile industry because of its capacity to produce transparent films .6.1.3 the waxy corn starch for the industry of the adhesives differs from the usual corn starch at the same time by its molecular structure and its characteristics of pasting. According to Watson, the pastes made containing waxy starch are long and cohesive, whereas those of normal corn starch are short and thick. The waxy corn starch is the principal starch of the adhesives used for the labels of bottles. These adhesives containing waxy starch give to the labels a resistance to the resolubilisation which prevents their takeoff of the bottle if they are wet or subjected to a strong moisture. Moreover, the waxy corn starches are usually used for the manufacture of gummed bands and adhesives for envelopes.

Paper mill

Principal progress in the technology of the manufacture of paper is partly related to the availability of new types of modified waxy corn starches. These starches bring primarily qualities of binder to the manufacturing process of paper, but they add also other essential characteristics, in particular the improvement of and its property paper weight of impression. Several patents were deposited on double mutants of but. Two were deposited on the genotype of corn wxsu2, one to use the starch like thickener with a stability at low improved temperature, and the other between rassissement of the bread. In the second case, the bread has a more marrowy, wet crumb after a fresher cooking and texture and aspect after conservation than the bread produced without this additive. Several patents of the company American Maize-products Company are based on new starches which can replace those chemically modified, containing all the gene wx. These starches present a whole a modification of viscosity, limpidity, aspect of the paste and resistance to the cycle congelation-defrosting.

Animal feeds

The food of the animals containing waxy corn began in the United States in the years 1940. A research report appeared in 1944 indicated that the waxy corn seemed to have the capacity of aaméliorer the effectiveness of food conversion. Many other food tests implying the porcine ones, the bovines with meat or milk as well as calves and the poultry were conceived to compare the food value of waxy corn with that of the normal toothed grain. In general, they showed an advantage for waxy corn. Seldom the investigations showed negative or contrary effects of the food with waxy corn grains. Increases at the same time in the production of milk and butyric content are not rare when the waxy corn is given to the milch cows in period of lactation. Moreover, an increase of 14% of the food effectiveness was noted in favor of waxy corn.

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