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Waxy corn (maize) was found in China in 1909. As this plant showed many peculiar traits, the American breeders long used it as a genetic marker to tag the existence of hidden genes in other maize breeding programs. In 1922 a researcher found that the endosperm of waxy maize contained only amylopectin and no amylose starch molecule in opposition to normal dent maize varieties that contain both. Until World War II, the main source of starch in the USA was tapioca but when Japan severed the supply lines of the States, they forced processors to turn to waxy maize. Amylopectin or waxy starch is now used mainly in food products, but also in the textile, adhesive, corrugating and paper industry. When feeding trials later on showed that waxy maize could produce more efficient feed gains than normal dent maize, interest in waxy maize suddenly mushroomed. Geneticists could show that waxy maize has a defect in metabolism precluding the synthesis of amylose in the endosperm. It is coded by a single recessive gene (wx). Waxy maize yield about 3.5% less than their normal dent counterparts and has to be isolated from any nearby normal maize fields by at least 200 meters. ==History== The exact history of waxy maize is unknown. The first mentions of it were found in the archives of the U.S. Department of Agriculture (USDA). In 1908, the Rev. J. M. W. Farnham, a Presbyterian missionary in Shanghai, sent a sample of seeds to the U.S. Office of Foreign Seed and Plant Introduction. A note with the seeds called it: “A peculiar kind of corn. There are several colours, but they are said to be all the same variety. The corn is much more glutinous than the other varieties, so far as I know, and may be found to be of some use, perhaps as porridge.” These seeds were planted on May 9, 1908, near Washington, D.C., by a botanist named Guy N. Collins. He was able to grow 53 plants to maturity and made a thorough characterisation of these plants, including photographs, which were published in a USDA bulletin issued in December 1909.〔Collins, G. N. (1909). ”A new type of Indian Corn from China.” Bureau of Plant Industry (Bulletin) 161: 1-30.〕 In 1915, the plant was rediscovered in Upper Burma and in 1920 in the Philippines. Kuleshov,〔Kuleshov, N. N. (1954). ”Some peculiarities in the maize of Asia.” (original version in Russian, St-Petersbourg, 1928) Annals of the Missouri Botanical Garden 41(3):271-299.〕 when screening the distribution of maize in Asia, found it in many other places. The discovery in China of a distinct type of maize bears the historical question whether maize was known in the Orient before the discovery of America. The question was considered closed at the end of the 19th century by De Candolle〔De Candolle, A. (1883). Origine des plantes cultivées. Marseille, Editions Jeanne Laffitte (republished in 1984).〕 who stated: ”Maize is of American origin, and has only been introduced into the old world since the discovery of the new. I consider these two assertions as positive, in spite of the contrary opinion of some authors.“ But the finding of this unique variety of maize suggested a re-examination of the question. He also states that Portuguese arrived in China in 1516, simultaneously introducing maize. Collins supposed that waxy maize has arisen by a way of mutation in Upper Burma.〔Collins, G. N. (1920). ”Waxy maize from upper Burma.” Science 52(1333): 48-51.〕 For some scholars it was difficult to conceive that from 1516 on the American plant had had time to penetrate into a wild country inaccessible to foreigners, to produce a mutation, and as such a mutant to spread from the Philippines to Northern Manchuria and the Primorsky region within three to four hundred years.〔 Nowadays we are able to counterpart both of these arguments. At first we know that the waxy mutation is quite common (see #Genetics). Secondly, the fact that maize, if introduced into Asia in Post-Columbian times, must have been rapidly accepted merely indicates that, like the potato in Ireland, it met an acute and pressing need.〔Mangelsdorf, P. C. (1974). ''Corn, Its Origin, Evolution and Improvement''. Cambridge, Massachusetts, The Belknap Press of Harvard University Press. ISBN 0-674-17175-6〕 Goodrich〔Goodrich, L. C. (1938). ”China’s first knowledge of the Americas.” Geog. Rev. 27: 400-411.〕 states that there are now in China some 6000 local histories called gazetteers written from A.D. 347 on. Maize was first accurately described in one of them, published in the sixteenth century. Ho,〔Ho, P. T. (1956). ”The introduction of American food plants into China.” Am. Anthrop. 57: 191-201.〕 an eminent Chinese historian, stated: “Summing up the introduction of maize into China, we may say that maize was introduced into China two or three decades before 1550 . . . ” It might be, as various students concluded, that maize reached Asia before 1492, but currently we are not aware of a single plant fragment, artifact, illustration, or written record to prove it. Therefore, any undocumented statement about its occurrence there in earlier times is to be regarded with scepticism until substantiated.〔〔Weatherwax, P. (1950). ”The history of corn.” The scientific monthly 71(1): 50-60.〕 Thus, the two assertions of De Candolle are still valid. In his publication, Collins characterised the new plants as possessing a number of unique characters. No indications of these characters in any recorded form of Zea mays had thus far been found. Several of the unique features combine to enable the plant to resist the drying out of the silks by dry, hot winds at the time of flowering. Although the plants produced such small ears that they could find no place in direct competition with the improved varieties, the possession of this adaptation gave the new type an economic interest, particularly in some parts of the semiarid Southwest. Consequently, the effort has been made to combine by hybridising the desirable characters of this small variety with those of larger and more productive types.〔Collins, G. N. (1914). ”Inheritance of Endosperm Texture in Sweet x Waxy Hybrids of Maize.” The American Naturalist 48(574): 584-594.〕 And when Collins found such a distinct difference in the appearance of normal and waxy maize endosperm, he suspected a difference in chemical composition, but the analysis did not yield any unusual results. The percentages of starch, oil, and protein were all within the normal range. Yet, he was intrigued by the physical nature of the starch, and wrote: “In view of the recent development of specialised maize products as human food, the unique type of starch may be of some economic importance." So actually, for many years the main use of waxy maize was a genetic marker for other maize breeding programs. Breeders were able to use some of the traits to “tag” the existence of hidden genes and follow them through breeding programs. It is possible that waxy maize would have become extinct again in the USA without this special application in breeding. In 1922, another researcher, P. Weatherwax of Indiana University in Bloomington, reported that the starch in waxy maize was entirely of a “rare” form called “erythrodextrin”, known today as amylopectin.〔Weatherwax, P. (1922). ”A rare carbohydrate in waxy maize.” Genet. 7: 568-572.〕 He found that this rare starch stained red with iodine, in contrast to normal starch which stained blue. Bates, French ''et al.''〔Bates, L. L., D. French, ''et al.'' (1943). ”Amylose and amylopectin content of starches determined by their iodine complex formation.” J. Am Chem. Soc. 65.〕 and Sprague, Brimhall, ''et al.''〔Sprague, G. F., B. Brimhall, ''et al.'' (1943). ”Some effects of the waxy gene in corn on properties of the endosperm starch.” J. Am. Soc. Agron. 35: 817-822.〕 confirmed that endosperm starch of waxy maize consists nearly exclusively of amylopectin. The presence of amylopectin in rice had been demonstrated previously by Parnell.〔Parnell, F. R. (1921). ”Note on the detection of segregation by examination of the pollen of rice.” J. Genet. 11: 209-212.〕 In 1937, just before World War II, G.F. Sprague and other plant breeders at what was then called Iowa State College had begun a crossbreeding program to attempt to introduce the waxy trait into a regular high-yielding hybrid maize. By this time, the waxy plant no longer had the peculiar structural traits noted by Collins, probably due to years of crossing into various genetic stocks. Only the unique endosperm had been retained. At this time, waxy maize was not so important because the main source of pure amylopectin still was the cassava plant, a tropical shrub with a large underground tuber.〔FAO (2004). ”Global cassava market study.” http://www.fao.org/docrep/007/y5287e/y5287e00.htm (14. Jan. 2006).〕 During World War II, when the Japanese severed the supply lines of the States, processors were forced to turn to waxy maize.〔Schopmeyer, H. H. (1943). ”Waxy cornstarch as a replacement for tapioca.” Ind. Eng. Chem. 35: 1168-1172.〕 Waxy maize appeared to be especially suitable for this purpose because it could be milled with the same equipment already extensively used for ordinary maize.〔Kiesselbach, T. A. and N. F. Petersen (1926). ”The segregation of carbohydrates in crosses between waxy and starchy types of maize.” Genet. 11(5): 407-422.〕 H. H. Schopmeyer has advised that the production of waxy maize in Iowa for industrial use amounted to approximately 356 metric tons in 1942 and 2540 tons in 1943.〔Schopmeyer, H. H. (1943). ”Waxy cornstarch as a replacement for tapioca.” Ind. Eng. Chem. 35: 1168-1172.〕 In 1944, there were only 5 varieties of waxy maize available for waxy starch production. In 1943, to cover all the special requirements for amylopectin, approximately 81650 tons of grains were produced. From World War II until 1971, all the waxy maize produced in the U.S. was grown under contract for food or industrial processors. In fact, most of the maize was grown in only a few counties in Iowa, Illinois, and Indiana.〔Crookston, R. K. (1979). ”The story of waxy corn maize varieties, uses and history.” Crops and soils 32(9): 11-13.〕 But in 1970, the Southern corn leaf blight epidemic (Helminthosporium maydis Nisik. and Miyake) swept the U.S. corn belt. At the same time, at least 80% of the maize being grown in the U.S. was susceptible to the blight because this maize contained the “Texas type” male-sterile cytoplasm, which allowed production of hybrid seed without mechanical or hand detasseling. As a result, there was a scramble in 1971 to find any kind of maize that had normal cytoplasm – cytoplasm that would resist the blight. Consequently, some seed of waxy maize worked its way into the market. Through backcrossing, also has been used extensively to transfer individual genes such as wx (waxy), o2 (opaque 2) and the Htl gene for resistance to the leaf blight was transferred to regular dent corn.〔Walden, D. B. (1978). Maize breedings and genetics. US, Wiley-Interscience publication.〕 Some farmers who fed this waxy grain to their beef cattle observed that animals thrived on it. Feeding trials were set up which suggested that the waxy maize produced more efficient weight gains than normal dent. Interest in waxy maize suddenly mushroomed, and this maize type abandoned the status of botanical curiosity and speciality product to become the subject of major research importance.〔 In 2002, an estimated 1,200,000 to 1,300,000 tonnes of waxy maize was produced in the United States on about 2,000 km², representing only 0,5% of the total maize production.〔US Grain Council (2002). ”Value enhanced-corn (VEC) quality report 2001-2002.” http://www.vegrains.org/documents/2002veg_report/toc/tablecont.html (30.01.06).〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Waxy corn」の詳細全文を読む スポンサード リンク
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