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1986 EC86-112 Origins, Adaptation, and Types of Corn W. L. Brown
M. S. Zuber
L. L. Darrah
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Brown, W. L.; Zuber, M. S.; and Darrah, L. L., "EC86-112 Origins, Adaptation, and Types of Corn" (1986). Historical Materials from University of Nebraska-Lincoln Extension. 4596. http://digitalcommons.unl.edu/extensionhist/4596
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Origins, Adaptations, and Types of Corn
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.._.. '""'' io f"rth"'"" of Coop""'" E><•ooioo wmk, Ao" of M•v 8 >Od J""' 30, 191 4 , '" ""'""''" whh The Cooperativ e Ex tension Service provi.des inf ormation and educational programs to all people w ithout regard to race, color, national ortg1n . sex or h andic ap. Origins, Adaptation, and Types of Corn* W .L. Brown, Pioneer Hi-Bred International, Inc., lA; M .S. Zuber, University of Missouri; L.L. Darrah, USDA-ARS, University of Missouri; and D.V. Glover, Purdue University ORIGIN OF CORN if less attention were given to determining corn's ori Corn (Zea mays L. ) is the only important cereal gin and more to understanding the remarkable varia indigenous to the Western Hemisphere. Apparently bility found within the species. originating in Mexico, it spread northward to Canada and southward to Argentina . Wh ile the possibility of Variability and Races secondary centers of orig in in South America cannot Re gardless of origin, corn has proven to be one be completely ru led out, the oldest (7 000 years) ar of the most adaptable and variable members of the chaeological corn was found in Mexico's Va ll ey of grass family. Its evolution, a large part of which ap Tehuacan . parently occurred under domestication, has resu lted The earliest "corn" of wh ich there is record is un in biotypes with adaptation ranging from the tropics mistakably corn. The female inflorescence of th is to the north temperate zone, from sea level to 12,000 5000 B.C. corn had reached a degree of specializa feet altitude and growing periods (planting to maturi tion that precluded the possibil ity of natural seed dis ty ) extending from 6 weeks to 13 months . semination. Thus, the oldest corn of record was Almost 300 races of corn have been described dependent 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, on ly two of which receive serious least 150 di st inct entities have been collected in consideration today. One is that teosin te (Zea mexi these areas . It was from certain of these races that cana ) is the wild progenitor of corn; the other is that most of the corns of North America were ultimately a wild pod corn, now extinct, was the ancestor of derived . domesticated corn While perhaps more students of corn seem to accept the first theory, others are Spread from Center of Origin equally convinced of the second . Following discovery, corn moved qu ickly to Eu Aside from its possible role in the origin of corn, rope, Africa and Asia . From Spain, it spread north eosinte has had major impact on its evolution. In ward to the short -growing -season areas of France. Mexico particularly, introgression between corn and Germany, Austria and eastern Europe, where selec teosinte has likely occurred for centuries and contin lion for early maturity has produced some of the ear ues to thi s day. The effects are apparent in the mor liest commercial vari eties of corn now avail able . In phology and cytology of both species. There is also Italy and Spain, early counterparts of man y South rea son to bel ieve that genes for re sistance to certain American races are evident even today . vi ruses have re ached corn through its introgression Although introduced into Africa soon after wi th teosinte . discovery, much of the corn now found in that con The origin of corn may never be known with cer tinent is derived from later introductions from the ta inty. One reason is that the hypotheses purporting southern U.S., Mexico and parts of eastern South to explain origin cannot be tested experimentally. America. Most of southern Africa's corn traces back Therefore, science would perhaps be better served to variet ies grown in the southern U S. in colonial *Contents reprinted f rom Nat ional Corn Handbook publication NCH-1 0. Contact Charles A . Francis, Extension Crops Specia list, for more information . 3 and post -colonial times. Corn of tropical middle The major environmental factors are: (1) daily (lowland) Africa is similar to the lowland and tropical maximum and minimum temperatures, (2) soil atmo corns of Central and South America . Africa has al sphere and moisture levels, (3) humidity of the atmo ways preferred white corns; and until recently, the sphere immediately surrounding the plant, (4) wind The most widely used and productive corns of movement, (5) day length, (6) light intensity, (7) air Asia are derived from Caribbean -type flints intro pollution, (8) soil type, (9) soil fertility, (1 0) number of duced in relatively recent times . However, older and days exceeding 50°F, (11) competition from other quite distinct types of corn can also be found, for ex plants including its intended neighbors as well as ample, among the hill people of Mindanao in south weeds, and (12) the disease-insect complex . ern Philippines . Included are some small-eared, Many of these factors interact in a complex early -maturing flints or pops that either have the manner to produce stress on the plant. The plant's capacity to grow and mature quickly before being reaction to stress is under genetic control, and devastated by downy mildew or carry some genetic differences among hybrids exist. Corn breeders are resistance to downy mildew. continuously developing and testing new genetic In the eastern Himalayas (Sikkim and Bhutan). a combinations in differing environments to find types distinctive type of popcorn is found whose Western that give the best agronomic performance over a Hemisphere progenitors seem to have disappeared . range of geographical locations and years. When and how the ancestor of th is corn reached Corn is grown from sea -level to altitudes of more Asia is not known . However, since it is not present than 12,000 feet and from the equator to about 50° on the Indian subcontinent to the south, it may have north and south latitudes. Compared to environ men reached the Himalayas by way of China and Tibet. tal conditions of the U.S. Corn Belt. many producing In any event, a search for similar corns in south Chi areas would be considered very much substandard . na and Tibet would seem justified. In harsh -environment areas. the varieties grown would be considered adapted because they Corn of the U.S. Corn Belt responded the best under the unfavorable growing Whereas most of the modern races of corn are conditions. The original open -pollinated varieties derived from prototypes developed by early native have become adapted through selection over time agriculturists of Mexico. Central and South America. by both man and the environment. one outstanding exception is solely the product of post -colonial North America-the yellow dent corns that dominate the U.S. Corn Belt, Canada and much Adaptation Within the Corn Belt of Europe today . The origin and evolution of this re World production of corn in the early 1980's ap markable race of corn have been clearly document proached 450 million metric tons annually, with the ed and confirmed . U.S. contributing over 48 percent of the total. Of U.S. In the early 1800's, two predominant races of annual production, the 13 Corn Belt states account corn of North America's eastern seaboard-the for about 82 percent . late -maturing Virginia Gourd seed and the early No area of the world equals the Corn Belt for high maturing Northeastern Flints-were first crossed, and yields . This is due to a combination of ideal soils and the superiority of the hybrid recognized and climate, advanced farmer know-how, and the suc described. The cross was repeated many times dur cess of corn breeders in developing hybrids with ing the western migration of settlers; and out of these high genetic potential. mixtures eventually emerged the Corn Belt dents, the Climate. Corn is considered a warm -weather most productive race of corn found anywhere in the crop. In the Corn Belt. average summer tempera world . tures range from 70° to 80° F daytime and exceed It was the highly selected varieties of Corn Belt 58° F at night. The average frost -free growing period dents that formed the basis of hybrid corn and the is over 140 days. Greatest yields are obtained where source of the first inbred lines used to produce hy 30 or more inches of rain occur during the growing brids . Germplasm from some of these varieties (Reid, season. In areas where rainfall is less than 20 Lancaster, Krug, etc.) still figure prominently in the inches, yields are much reduced unless irrigation is ancestry of hybrids used in the Corn Belt even to used. this day. Rainfall distribution greatly influences maximum yields, especially for the 3 -week period centered around tasseling . In the southern part of the Corn ADAPTATION OF CORN Belt, high -temperature stress and rainfall deficien cies often occur in late July and August . Therefore, Definition and Adaptation Worldwide farmers of this region try to avoid having corn tassel Adaptation in corn means good performance with during this dry, hot period by planting earlier and us respect to yield and other agronomic characteristics ing earlier -flowering hybrids . in a given environment. The environment includes all Maturity. Maturity of corn hybrids is a genetic conditions to which the plant is subjected during the characteristic and is generally defined as the period growing season (from pre -seedling emergence to from germination to when the kernel ceases to in harvest maturity). crease in weight. In the northern Corn Belt. early hy- 4 brids often re ach physiological maturity in less th an duces long glumes enclosing each kernel individual 1 00 days; whereas in the extreme south, 150 or ly, such as occurs in many other grasses. more days may be needed . These day periods are measures of relative maturity. Dent Corn Hybrids have traditionally been classified into 1 5 The U S Corn Belt dents originated from the hy maturity groups ranging from Agricultural Experiment bridization of the Southern Dent or late -flowe ring Station (A ES) 100 to AES 1500 (earliest to latest). maize race called Gourdseed, and the early However, maturity classification can be made more flowering Northern Flints . Dent corn is characterized precise by determining the total heat units required by the presence of corneous. horny endosperm at from emergence to physiolog ical maturity . A heat the sides and back of the kernels, wh ile the central unit measure commonly used accumulates th e daily core is a soft, floury endosperm extending to the excess of average temperature over 50° F, where: crown of the endosperm where, upon drying, it col average temperature= (maximum+ minimum) -:- 2. lapses to produce a di stinct indentation. Degree of Ea rly hybrids grown in the northern Corn Belt cla ssi denting vari es with the genetic background . Nearly fied as 1 00 -day matu rity may re qu ire 90 or less days al l varieties grown in the U.S. are yel low, with only a to re ach maturity when grown further south whe re few whit e end osperm types grown. he at unit accumulat ion is more rapid . Dent corn is used prim arily as anim al food , but Adapted hybrid development. Hybrids have also serves as a raw material fo r indust ry an d as a been developed th at are adapted from Nebraska to staple food. Upwards of 93 pe rcent of dent corn pro Ohio. However, the environmenta l conditions differ duced (inclu ding the corn equivalent of by -product widely from west to east especially rainfall patterns, feed s from corn processing) is used as animal feeds. daily minimum and maximum temperatu res, and the However, it is still an important human food and in disease complex. For example, the hotter, drier con dust rial mate ri al, entering into many specialized pro ditions of the western Corn Belt are le ss favorable ducts vi a the dry - or wet -mil ling industry in the U.S. for leaf di seases caused by H elminthosporium spp. Yellow dent corn se ll s at market price as it enters and anthracnose, but more conducive to viral infec th e norma l feed gra in or mi ll ing channels. However, tion , bacteri al wilt and smut. For thi s reason, devel white dent often re ceives a premium price in the opment of hybrids adapted from west to east has dry -milling in dustry, where it is utilized for certa in hu been relat ively difficult and requires large -scale test man food products because of its whiter starch. ing over a number of location s and years. Number of fro st -free days decreases from th e Flint Corn southern to northern Corn Belt: however, hours of The fl int corns mostly have a thick, hard, vitreous daylight on June 22nd are much longer in the north (glassy) or corneous endosperm layer surrounding a than in the south . Sunlight intensity is greater in the sm all, soft granular center . The relative amounts of western and northern Corn Belt because these sec- soft and corneous starch, however, vary in different ions have less cloudy weather. variet ies . Generally, the kernels are smooth and The resu lt of intensive corn breeding efforts over rounded. and the ears long and slender with a com the past four decades has been better ad aptation to paratively small number of rows or kernels. In tem the many environments under which corn is grown . perate zones, flint corn often matures earlier, ger min ates better, has more spring vigor, more tillers and fewer prop roots than dent strains. Ve ry little flint corn is produced and util ized in the TYPES OF CORN U.S today, although it was undoubtedly grown ex Corn variation may be artificially defined accord tensively up through colonial times. Generally, yields ing to kernel type as fo llows dent, fli nt, flour, sweet, are lower than our Corn Belt dents, in part because pop and pod corn . Except for pod corn. these divi of relatively little breeding work done. Flints are more sions are based on the quality, quantity and pattern exten sively grown in Argentina and other areas of of endosperm composition in the kernel and are not South America, Lat in America and southern Europe indicative of nat ural relationships . where th ey are used for feed and food . Endosperm composition may be ch anged by a single gene diff erence, as in the case of floury (f/) ve rsus fli nt (FI) , su gary (su) versus starchy (Su) , Flour Corn waxy (wx) versus non -waxy (Wx ), and other single This is one of the oldest types of corn, tracin g recessive gene modifiers that have been used in back to th e ancient Aztecs and Incas. American In breeding special -purpose types of corn. The quantity dians ground the soft kernels for flour. Floury maize or volume of endosperm conditioning the size of the ty pes have soft starch throughout, with practically no kernel (e.g., the difference between dent and fli nt hard, vi treous endosperm and thus are opaque in corns or flint corn and popcorn) is po lygenic and, in kernel phenotype. Kernels tend to shrink uniformly the latter example, is of some taxonomic signifi upon drying, so usually have litt le or no denting . cance. When dry, they are easy to grin d, but may mold on The pod corn tra it is monogenic and more of an the mature ear in wet areas. ornamental type. The major gene involved (Tu ) pro - In the US., flour corn has li mited production and 5 is restricted to the drier sections. It is grown widely genetic type is not re adily identifiable by cultivar in the Andean reg ion of South America. name alone. At least 13 endosperm mutants , in I combination with sugary, have been studied for im Sweet Corn provi ng sweet corn . Except for sugary, the genes . The followi ng genetic model featuring primary used in breeding act diffe rently to produce the taste 1sol at1on groups for naming "vegetable corns" has and texture deemed desira ble for sweet corn . been suggested by the industry: Augmented sugary kernel types . In these sweet -t,. .. I. Sugary mutants corns, the sugars are modified (increased) by the ·~ ' A . Standard sugary (su) action of other genes, either parti al ly or completely ...... - B. Aug mented sugary Major modifier genes of ke rne l sweetness are 1 . Pa rtial modification shrun ken -2 (sh2) and sugary en hancer (se). In pa r a. Heterozygous shrunken -2 (sh2) ti al modifications, the sugary (su ) kern els are modi b. Heterozygous sugary en hancer (se) ti ed by the segregation of major modifier genes such c . Heterozygous shrunken -2 and sugary th at about 25 percent of the kern els are double enhancer (sh2 and se) mutant endosperm types possessing th e enh anced 2. Complete (1 00%) mod if ication benefits of the modifier . The addition of th e sugary a. Homozygous sugary enhancer (se) enhancer (se) gene alon g with one of the major II . Shrunken-2 (sh2) modifier genes (e.g., sh2 ) will further modify some of Ill . Brittle (bt) the sugary kern els io ar: Ot.-'1 44 percent double IV. Britt le -2 (bt2) mutant endosperm types ra th •,jr than 25 percent V. Amyl ose -extender (ae) Du ll (du) Waxy (wx) In complete (1 00 per c 8 ~ 1 t ) modification, the sug VI Dent (vegetable) ary (su) kernels are all :nod ified with the sugary _ VII. Additional classes as new genes are used enhancer (se) gene to produce the double comb ina tion (su se) for obtaining maximum benefit from the Isolation wi ll be require d between major groups se gene . Other major modifier genes of ke rn el identified by a Roman numeral. Isolation is suggest sweetn ess are: britt le (bt), brittle -2 (bt2), shrunken ed but not require d between subgroups with in a ma (sh) and sh runken -4 (Sh4 ). Other genes wi th mi nor jor group. No isolation is needed for cultivars wi thin modifying effects of kernel sweetness are: dull (du), the same class ifi cation. floury (f/ ), flou ry -2 (f/2) opaque (o), opaque -2 (o2 ), Standard sugary kernel types . Sweet corn, sugary -2 (su2), and waxy (wx). Some are known to commonly referred to as the standard sugary (su) be present in sweet corn backgrounds either in the corn , is thought to have originated from a mutation in segregating or homozygous state . the Peruvian race Chullpi. Most certainly it was Other mutants producing sugary kernels includ e grown and used by native American Indians in pre the single -mutant endosperm genes shrunken -2 Columbian ti mes . (sh2), brittle (bt ) and britt le -2 (bt2), and the mu lti In sweet corn , the sugary gene prevents or re pie -mutant endosperm genes amyl ose -exte nder, tards the normal conversion of sugar into starch dur dul l, waxy (ae du wx). ing endosperm development, and the kernel accu Precautions with modified endosperm sweet mulates a water -soluble polysacchari de called "phy corn to avoid xenia . Isolation of "sweet corn" cul toglycogen." As a re su lt, the dry, sugary kern els are tivar plantings of different genetic types is necessary wrinkled and glassy. The higher content of water to prevent cross -pollination . Xen ia is the immediate solu ble polysaccharide adds a te xtu re quality factor effect of fore ign pollen on a variety; on sweet corn in addition to sweetness . In th e U.S , sweet corn is (su), it will prod uce a starc hy kernel. Isolation can be eaten in the immature mil k stag<> and is one of th e obtained by planting at a differe nt time, planting cu l most popu lar veg etables. tivars of different maturities, pl anting "upwind" of Sweet corn in th e U.S. is more im portant eco prevailing wind dire ction , or provi ding barriers and nomically than its limited commercial production border rows. All of these methods will reduce the would in dicate , because it is consumed dire ctly as isol ation distances necessary. On a practical basis, human food (fresh market or canned and froze n commercial growers should pro vi de at le ast 50 feet products) rather than ind ire ctly as livestock feed. separation, plant upwind of normal field corn , and The bu lk of sweet corn production is confi ned to th e use fou r or more border ro ws. northern tier of states and to south ern Florida as a winter crop . In th e broader sense, vegetable corns include al l com harvested and eaten whil e th e kernels are still Popcorn tender and before all of the sugars are converted to Popcorns are perhaps th e most primiti ve of the starch . Thi s defin ition in cludes "roasting ears" of survi ving ra ces of maize. This corn type is charac selected field corns . terized by a very hard , corneous endosperm con Tod ay, th e standard sugary corns are being taining on ly a small portion of soft sta rch. Popcorns modifi ed with other endosperm genes and gene are essentially small-kerneled fli nt types . The kernels combination s th at control sweetness to develop new may be either pointed (ri ce -l ike ) or round (pearl cultivars . As a re sult, growers must consider genetic like). Some of the more re cently developed popcorns ty pe when making selections for planting . The have thick pericarps (seed coats), whil e some primi - 6 tive semi -popcorns, such as the Argentine popcorns, Products made from waxy corn are used by the have thin pericarps. food industry as st abilizers and thickeners for pud Popcorn is a relatively minor crop compared to dings, pie fillings, sauces, gravies, retorted foods , dent corn . It is used primarily for human consump salad dressings, etc. Other waxy products are used tion as freshly popped corn or as the basis of pop as remoistening adhesives in the manufacture of corn confections. Isolated planting is not necessary, gummed tape, in adhesives and in the paper indus since there are no major xenia effects on popping try . Waxy grain is also grown as a feed for dairy expansion and many popcorns are cross -steril e with cattle and livestock. field corn. Waxy corn is usually grown under contract for the Most popcorn acreage is grown under contract. major wet millers and exporters . Premiums are pa id Although conditions for growing popcorn are the to the growers of waxy corn for wet milling because same as for dent corn, special harvesting, drying and it must be isolated during production, harvesting, storage practices are necessary to maintain popping transporting and storing. Since waxy is a recessive quality (see NCH -5, "Popcorn Production and Mar characteristic, isolation from dent corn is necessary keting"). to prevent loss of its peculiar starch properties High-amylose corn . Amylomaize is the generic Pod Corn name for corn that has an amylose content higher Pod corn (tunicate maize) is more of an orna th an 50 percent. Th e endosperm mutant am ylose mental type . The major gene involved (Tu ) produces extender (a e) fo und by R. P. Bear in 1950, increases long glumes enclosing eacr kernel individually, such the amylose content of the endosperm to about 60 as occurs in many other grasses The ear is also percent in man y dent backgrounds. Modifying fac enclosed in hu sks, as with oth er ty pes of corn. tors alter th e amylos e contents as well as desira ble Homozyg ous pod corn usually is highly self agronomic characte ristics of th e grain. Th e amy sterile. and the ordinary type of pod corn is heterozy lose -extender gene expression is ch aracterized by a gous Pod corn may be dent, sweet, waxy, pop, fli nt tarni shed, translucent, som etimes semi -full kernel or floury in endosperm characteristics. It is merely a appearance . curiosity and is not grown commercially. Hi gh -amyl ose grain is grown exclusively for wet mi ll ing . The two types produced commercially are Specia l-Purpose Corns Cl ass V (amylose conte nt, 50 -60 pe rcent) and Class Corn may be altered by genetic mea ns to pro VII (amylose content, 70-80 percent). Th e starch duce modifications in starch, protein. oil and other from high -amylose corn is used in the textile indus properties . As a result of modifications of ord inary try, in gum candies (where its tendency to form a gel dent types, new corn specialties have been created . aids production), and as an adhesive in the Among them are waxy -maize, amylomaize. and manufacture of corrugated cardboard. hi gh -lysine or modifi9d -protein corn. High -amylose corn yields vary depending upon Waxy corn . Th is special -purpose type was intro location, but average only 65 -75 percent of that of duced to the U S. from China in 1908. Although Chi ordinary dents. Present production acreage is lim ited na was the original source, waxy (wx) mutations to that grown under contract arrangements for wet have since been found in American dent strains. Its millers. Premiums are paid to growers because of name derives fro m the waxy appearance of the en decreased yields and the necessity to isolate high dosperm exposed in a cleanly cut cross -section. amylose corn during production, harvesting, trans Common corn starch is approximately 73 percent porting and storing . The premium depends upon amylopecti n and 27 percent amylose ,...whereas waxy class, year and desired acreage . starch is composed entirely of amylopectin, which is High-lysine corn. This is the generic name for the branched molecular form . Ordinary cornstarch corn having an improved amino acid balance, thus a sta ins blue with 2 percent potassium iodide solution , better protein quality for feeding and food use com whereas waxy cornstarch stains a reddish brown . pared to ordinary dent types. E. T. Mertz in 1964 Th e waxy gene also expresses itself in the pollen discovered that the single recessive gene, opaque -2 with this staining reaction, wh ich is an aid in breed (o2 ), reduced zein in the endosperm and increased ing . the percent of lys ine to improve nutritional quality . Sign ificant ad van ces in ytelds have been made Other genes with similar gross effects on protein wrt h the newer waxy hybrids . Wh ile the overall aver quality exist in corn, but attempts to improve corn age may run so mewh at less th an dent corn hybrids, protein quality have been primaril y based on use of the newer waxy hybrids are more comparable to the the opaque -2 gene and modified opaque -2 germ better dents in yields . plasm . Waxy corn has carved out a formidable position The opaque -2 gene is charactenzed by a soft, as the raw material of waxy cornstarch produced by chalky , non -transparent kernel appearance, hav ing certain wet -corn millers in the U.S., Canada, Europe, practi cally no hard vitreous or horny endosperm . etc., for industry and food uses . Wa xy starch and Undesirable kernel characteristics (e.g. , kernel and modified waxy starches are sold extensively world ear rots) and insect and rodent damage can be a wide because of their stability and other properties of problem with the soft opaque -2 chalky phenotypes . the ir solutions. Improvements in res istance to ear and kernel rots 7 ' ~! have been substanti al with se lection, and a number Current U.S. use of high -lysine corn is re stricted of good hybrids exi st. On the average, the opaque -2 because of (1) yield differentials compared to normal hybrids yield about 7-1 0 percent lower than their corn and (2 ) the corn -to -soybean oil I meal pr ice re normal counterparts . lationship. Demand fo r high -qual ity protein corn in A promising approach to overcoming some of the the U.S. is insufficient to command a premium price. deficiencie s of the homozygous opaque -2 materials However, high -lysine corn is grown to a lim ited ex involves the visual selection of specific modifiers of tent as a feed for poultry, swine, dairy cattle and oth op aque -2 . It is fairly easy to develop modified, vitre er livestock production needs. In corn -dependent ous opaque -2 materials with good ear rot and grain countries where normal corn is a major staple of the insect resistance. Selections must include en do human diet, or where high -quality protein supple sperm chemical analyses to maintain high levels of ments for animal feeding are scarce, yield is a protein quality . secondary consideration . Some high -lysine materials Another approach to endosperm textural modifi are to the point of development where it may be cation to solve so me of the problems associated with cost -efficient to grow quality -protein corn as a opaque -2 corn has been use of the double mutant specialty crop. combination , sugary-2 opaque -2 (su2 o2) . This Ornamental corn . The so -called ornamental or modification has im proved kernel vitreousness, den "Indian" corns commonly show segregation for al sity and re sistance to kernel breakage. The im proved leles of several genetic factors th at control the pro vitreous of su2 o2 is accompanied by protein quality duction of anthocyan in s and related pigments in the at least equal to the unmodified opaque-2 materials; aleurone, pericarp and pl ant tissues of corn. The however, at this point, yields are 80-85 percent of kernels may be segregating for various color ex pres normal dents. sions; and varigation of color may even be ex High -lysine grain can be an important source of pressed with in a kernel, depending upon the genetic high -q uality protein in th e diets of nonruminants; and factors involved and their interaction during develop nutritional studies have confirmed the potential value ment of the kernel. of high -lysine corn in helping to meet the world's hu Ornamental corns may be dent, sweet, pop, fl int or man and an imal nutritional needs . For the present, floury endosperm types. Apart from genetic studies, they loss of calories per acre is the trade -off for in are a curiosity and are only grown for ornamental and creased amounts of high -quality protein . decorative purposes. 8