Origin, Adaptation, and Types of Corn W
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NATIONAL CORN HANDBOOK THE CORN CROP NCH-10 Origin, Adaptation, and Types of Corn W. L. Brown, Pioneer Hi-Bred International, Inc., IA; M. S. Zuber, University of MIssouri; L. L. Darrah, USDA-ARS, University of MIssouri; and D. V. Glover, Purdue University Reviewers R. G. Creech, Mississippi State University A. A. Fleming, University of Georgia K. F. Schertz, USDA-ARS, Texas A&M University A. F. Troyer, DeKalb-Pfi zer Genetics, IL ORIGIN OF CORN attention were given to determining corn’s origin and Corn (Zea mays L.) is the only important cereal more to understanding the remarkable variability found indigenous to the Western Hemisphere. Apparently within the species. originating in Mexico, it spread northward to Canada and southward to Argentina. While the possibility of Variability and Races secondary centers of origin in South America cannot Regardless of origin, corn has proven to be one of be completely ruled out, the oldest (7000 years) the most adaptable and variable members of the grass archaeological corn was found in Mexico’s Valley of family. Its evolution, a large part of which apparently Tehuacan. occurred under domestication, has resulted in biotypes The earliest “corn” of which there is record is with adaptation ranging from the tropics to the north unmistakably corn. The female infl orescence of this temperate zone, from sea level to 12,000 feet altitude 5000 B.C. corn had reached a degree of specialization and growing periods (planting to maturity) extending that precluded the possibility of natural seed dissemi- from 6 weeks to 13 months. nation. Thus, the oldest corn of record was dependent Almost 300 races of corn have been described upon man for its survival. from Mexico, Central and South America, and the Numerous theories of origin have been offered Caribbean. Although many appear synonymous, at over the years, only two of which receive serious con- least 150 distinct entities have been collected in these sideration today. One is that teosinte (Zea mexicana) areas. It was from certain of these races that most of is the wild progenitor of corn; the other is that a wild the corns of North America were ultimately derived. pod corn, now extinct, was the ancestor of domesti- cated corn. While perhaps more students of corn seem Spread from Center of Origin to accept the fi rst theory, others are equally convinced Following discovery, corn moved quickly to Europe, of the second. Africa and Asia. From Spain, it spread northward to Aside from its possible role in the origin of corn, the short-growing-season areas of France, Germany, teosinte has had major impact on its evolution. In Mexico Austria and eastern Europe, where selection for early particularly, introgression between corn and teosinte maturity has produced some of the earliest commer- has likely occurred for centuries and continues to this cial varieties of corn now available. In Italy and Spain, day. The effects are apparent in the morphology and early counterparts of many South American races are cytology of both species. There is also reason to be- evident even today. lieve that genes for resistance to certain viruses have Although introduced into Africa soon after discovery, reached corn through its introgression with teosinte. much of the corn now found in that continent is derived The origin of corn may never be known with cer- from later introductions from the southern U.S., Mexico tainty. One reason is that the hypotheses purporting to and parts of eastern South America. Most of southern explain origin cannot be tested experimentally. There- Africa’s corn traces back to varieties grown in the fore, science would perhaps be better served if less southern U.S. in colonial and post-colonial times. Corn Cooperative Extension Service Iowa State University Ames, Iowa 50011 May 1985 of tropical middle (lowland) Africa is similar to the low- and moisture levels, (3) humidity of the atmosphere land and tropical corns of Central and South America. immediately surrounding the plant, (4) wind move- The most widely used and productive corns of ment, (5) day length, (6) light intensity, (7) air pollu- Asia are derived from Caribbean-type fl ints introduced tion, (8) soil type, (9) soil fertility, (10) number of days in relatively recent times. However, older and quite exceeding 50°F, (11) competition from other plants distinct types of corn can also be found, for example, including its intended neighbors as well as weeds, and among the hill people of Mindanao in southern Philip- (12) the disease-insect complex. pines. Included are some small-eared, early-maturing Many of these factors interact in a complex man- fl ints or pops that either have the capacity to grow ner to produce stress on the plant. The plant’s reac- and mature quickly before being devastated by downy tion to stress is under genetic control, and differences mildew or carry some genetic resistance to downy among hybrids exist. Corn breeders are continuously mildew. developing and testing new genetic combinations in In the eastern Himalayas (Sikkim and Bhutan), a differing environments to fi nd types that give the best distinctive type of popcorn is found whose Western agronomic performance over a range of geographical Hemisphere progenitors seem to have disappeared. locations and years. When and how the ancestor of this corn reached Asia Corn is grown from sea-level to altitudes of more is not known. However, since it is not present on the than 12,000 feet and from the equator to about 50° Indian subcontinent to the south, it may have reached north and south latitudes. Compared to environmen- the Himalayas by way of China and Tibet. In any tal conditions of the U.S. Corn Belt, many producing event, a search for similar corns in south China and areas would be considered very much substandard. In Tibet would seem justifi ed. harsh-environment areas, the varieties grown would be considered adapted because they responded the Corn of the U.S. Corn Belt best under the unfavorable growing conditions. The Whereas most of the modern races of corn are original open-pollinated varieties have become adapt- derived from prototypes developed by early native ed through selection over time by both man and the agriculturists of Mexico, Central and South America, environment. one outstanding exception is solely the product of post-colonial North America—the yellow dent corns Adaptation Within the Corn Belt that dominate the U.S. Corn Belt, Canada and much of World production of corn in the early 1980s ap- Europe today. The origin and evolution of this remark- proached 450 million metric tons annually, with the able race of corn have been clearly documented and U.S. contributing over 48 percent of the total. Of U.S. confi rmed. annual production, the 13 Corn Belt states account for In the early 1800s, two predominant races of corn about 82 percent. of North America’s eastern seaboard—the late-matur- No area of the world equals the Corn Belt for high ing Virginia Gourdseed and the early-maturing North- yields. This is due to a combination of ideal soils and eastern Flints—were fi rst crossed, and the superiority climate, advanced farmer know-how, and the suc- of the hybrid recognized and described. The cross was cess of corn breeders in developing hybrids with high repeated many times during the western migration of genetic potential. settlers; and out of these mixtures eventually emerged Climate. Corn is considered a warm-weather the Corn Belt dents, the most productive race of corn crop. In the Corn Belt, average summer temperatures found anywhere in the world. range from 70° to 80°F daytime and exceed 58°F at It was the highly selected varieties of Corn Belt night. The average frost-free growing period is over dents that formed the basis of hybrid corn and the 140 days. Greatest yields are obtained where 30 or source of the fi rst inbred lines used to produce hybrids. more inches of rain occur during the growing season. Germplasm from some of these varieties (Reid, Lan- In areas where rainfall is less than 20 inches, yields caster, Krug, etc.) still fi gure prominently in the ances- are much reduced unless irrigation is used. try of hybrids used in the Corn Belt even to this day. Rainfall distribution greatly infl uences maximum yields, especially for the 3-week period centered ADAPTATION OF CORN around tasseling. In the southern part of the Corn Belt, high-temperature stress and rainfall defi ciencies often Defi nition and Adaptation Worldwide occur in late July and August. Therefore, farmers of Adaptation in corn means good performance with this region try to avoid having corn tassel during this respect to yield and other agronomic characteristics dry, hot period by planting earlier and using earlier- in a given environment. The environment includes fl owering hybrids. all conditions to which the plant is subjected during Maturity. Maturity of corn hybrids is a genetic the growing season (from pre-seedling emergence to characteristic and is generally defi ned as the period harvest maturity). from germination to when the kernel ceases to increase The major environmental factors are: (1) daily max- in weight. In the northern Corn Belt, early hybrids often imum and minimum temperatures, (2) soil atmosphere reach physiological maturity in less than 100 days; whereas in the extreme south, 150 or more days may 2 be needed. These day periods are measures of rela- Dent Corn tive maturity. The U.S. Corn Belt dents originated from the Hybrids have traditionally been classifi ed into hybridization of the Southern Dent or late-fl owering 15 maturity groups ranging from Agricultural Experiment maize race called Gourdseed, and the early-fl owering Station (AES) 100 to AES 1500 (earliest to latest).