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611 Joanne Lane, DeKalb, IL 60115
* Corresponding author (atroyer{at}uiuc.edu).
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMETHODSRESULTSDISCUSSIONREFERENCES |
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONREFERENCES |
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When the new breed has spread widely, it gives rise to new strains and sub breeds, And the best of these succeed and spread, supplanting other and older breeds; And so always onwards in the march of improvement.—Charles Darwin 1868
DARWIN (1859), in The Origin of Species, notes the association of wide adaptedness with much taxonomic subdivision. He states that this association occurs because the large area occupied by the widely adapted taxonomic division necessarily contains many environmental or man-made niches where either natural selection or human (artificial) selection causes the formation of subdivisions. Darwin was well aware of the importance of time (how long) and of space (where) to evolution; transformation in time deals with changes in adaptedness, as when a species acquires new characteristics. Mayr (1997) states evolutionary effects usually answer "why" questions determined by inference from historical narrative.
Development and sale of open-pollinated cultivars emphasized local adaptation due to natural selection, but some open-pollinated cultivars were popular and widely grown due to human selection. Hybrids eliminated much of the justification for local adaptation; where the seed was developed and produced no longer greatly mattered. Successful, research-oriented, hybrid seed corn companies grew larger by selling more widely adapted hybrids (Troyer, 1996). Selection for widely adapted hybrids ultimately favored germplasm from the more popular, widely grown open-pollinated cultivars containing more genes for adaptedness (Allard, 1988; Vladutu et al., 1999; Tuberosa and Phillips, 2002) to the U.S. Corn Belt.
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All companies started with the same public inbreds, and surviving companies self-pollinated superior competitor hybrids to develop newer inbreds. The MBS 2002 Genetic Handbook of current inbreds lists Pioneer brand hybrids (including inbred LH123 from Pioneer brand hybrid 3535) in the background of 157 inbreds, and lists only seven inbreds from other company's hybrids (Brayton, 2002). Why so many Pioneer brand hybrids? Pioneer Hi-Bred market share increased from 22% in 1973 to 44% in 1996 (Pioneer Hi-Bred International, 1997). If the goal is to increase market share, it is logical to use breeding material (commercial hybrids) that increased market share. Product performance is heritable. Since 1970, Pioneer hybrids do not contain cytoplasmic male sterility that would complicate their use as breeding material. Former Chairman and President of Pioneer Hi-Bred International twice opined that developing inbreds from competitors' commercial hybrids was all right in a speech about germplasm ownership to the American Seed Trade Association (Brown, 1984).
Selection for widely adapted hybrids causes the background to resemble Fig. 1. A myriad of corn germplasm entities exist (Labate et al., 2003), and many are used in small amounts (<1%). In 1940, thousands of U.S. seed corn companies existed, but only about 300 have survived. Iowa went from 500 hybrid seed corn companies in 1940 to 100 in 1957 (Johnson, 1957) to 28 in 1997 (Troyer, 2000). Much noncompetitive germplasm left with noncompetitive companies. In the 1970s, breeding strategy changed from finding new hybrids among many inbreds to developing fewer, but more widely adapted inbreds, thus fewer backgrounds (Troyer, 1996). I believe Fig. 1 closely represents the present-day background of U.S. hybrid corn as a group. I have searched in vain for other background sources that exceed 1% (324000 ha, 800000 acres, or 250000 bags of hybrid seed) of annual, present-day U.S. corn production.
I've searched historical records to trace the succession of cultivars and inbreds. I've attempted to explain not only what open-pollinated cultivars and first-cycle landmark inbreds make up the background but also when, where, how, why, and by whom they were developed. This paper provides additional historical narratives of backgrounds, provides corrections to Background of U.S. Hybrid Corn (Troyer, 1999), and briefly discusses human (artificial) selection, natural selection, and food production. I present additional background results generally from greater to lesser amounts under germplasm headings like those in Fig. 1. Germplasm designation in all-capital letters imitates Smith et al. (1990), Troyer (1999), and Fig. 1 of this paper, indicating the same identical germplasm.
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The original and improved strains of Reid Yellow Dent and their known background percentages are as follows: IODENT REID, 13%; TROYER REID, 12%; OSTERLAND REID, 11%; BSSS (Stiff Stalk Synthetic also including Iowa inbreds B14A, B64, and B68 shown under FOREIGN in Fig. 1), 8%; REID YELLOW DENT per se, 4%; FUNK REID F3 (Illinois inbred R4), nearly 2%; and FUNK STRAIN 176A (Indiana inbred 38-11) is slightly >1% of the documented U.S. hybrid corn background. Ried Yellow Dent totals 51% of the documented U.S. hybrid corn background (Fig. 1).
IODENT REID
Troyer (1999) describes Iodent Reid and its derivatives in some detail. A newer finding indicates Lindstrom LE (Long Ear) in Modern Iodent Inbreds and in Early Iodent Inbreds is Richey Lancaster inbred LAN (see LANCASTER SURECROP in this paper). The amount of known Iodent Reid in U.S. hybrid corn background stays the same, but the backgrounds of Iodent Reid and Lancaster Surecrop and the amount of Lancaster Surecrop in the background of known U.S. hybrid corn change (Fig. 1). A brief review of Iodent Reid follows:
Iodent is an abbreviation of Iowa Experiment Station Reid Yellow Dent. Perry Holden brought Reid Yellow Dent to Iowa from Bloomington and from Taylorville, IL (Troyer, 2004). It was a full-season corn for southern Iowa. He and Iowa State College spread Reid Yellow Dent throughout Iowa beginning in 1902. Prof. Lyman C. Burnett of Iowa State College used the ear-to-row method to select for earliness and yield in Reid Yellow Dent from 1909 to 1922 to develop Iodent Reid. Dr. Jenkins started inbreeding Iodent Reid at Iowa State College in 1922. He separated inbreds IDT and I205 during inbreeding (probably at S3). Dr. Ernest W. Lindstrom finished IDT (also known as I205A). See Fig. 1 (Troyer, 1999).
Modern Iodent Inbreds were developed by Raymond Baker at Johnston, IA. He used hybrid B164 by LE as the nonrecurrent source of longer ears in part of a 16 ha (40 acres) detasseled field to make seed that was 87.5% Iodent Reid in 1942. I believe Lindstrom LE was in fact inbred LAN from Lancaster Surecrop (Lindstrom, 1931). This eliminates Lindstrom LE and increases Lancaster Surecrop as known backgrounds in Fig. 1. Mr. Baker selected for ear length at harvest, using ears of the male as comparative checks. He kept fewer than 200 ears from the B164 x LE nonrecurrent portion of the field. These cycle two selections resulted in three very important commercial inbreds (R.F. Baker, 1992, personal communication; Troyer, 1999).
Early Iodent Inbreds resulted from materials that Mr. Baker and I started at Mankato, MN, in 1958. My objective was to develop earlier versions of Baker's Modern Iodent Inbreds (adapted in south-central Iowa) using the Rinke method (Rinke and Sentz, 1961). Mr. Baker chose one early Pioneer inbred with Iodent Reid in its background, and I chose an early hybrid A509/A556 (adapted in south-central Minnesota) as a nonrecurrent donor parent. Minnesota inbred A509 has inbreds A78 (Northwestern Dent) and A109 (Osterland Reid) in its background. Inbred A556 has inbreds B164 (Troyer Reid) and A237 (Reid Yellow Dent) in its background. These three early inbreds each contributed excellent yield and very good stalk strength to their hybrids. I did the selection at Mankato using twice-normal plant densities and nitrogen fertilizer. I typically grew 1000 to 1200 plants of each segregating population and chose the earlier-flowering 10 or 12 plants (1%) to self, to backcross, or to sib mate. At harvest, the best ears from the best plants were selected. These cycle three selections were the sole background of several very important commercial inbreds during the 1970s and 1980s (Troyer, 1999).
Iodent Reid accounts for 13% of the documented U.S. hybrid corn background tracing back to Iowa inbred lines I205 and IDT (also known as I205A) (Coors et al., 1993; Fig. 1).
BSSS STIFF STALK SYNTHETIC
Dr. Sprague synthesized Stiff Stalk Synthetic from 1932 to 1934 at Arlington Farms, VA, where the Pentagon now stands. He crossed 16 inbreds, including two that were second-cycle inbreds, so a total of 20 parent inbreds were involved (Table 1; Hallauer et al., 1983). The inbreds had yellow endosperm and above-average stalk quality. Fifteen of the 20 inbred-parent slots (75%) trace back to improved strains of Reid Yellow Dent (six from Troyer Reid, three from Iodent Reid, two from Funk Strain 176A, and one each from Black Reid, Krug Reid, Osterland Reid, and Walden Reid). The other five inbreds include one each from Illinois Two Ear (from Chester Leaming), Illinois High Yield (from an indistinguishable cultivar), Illinois Low Ear (from Chester Leaming), Eichenberger Clarage, and Kansas Sunflower (ILL12 from Kansas Sunflower; D.R. Sywassink, 2003, personal communication). Dr. M.T. Jenkins developed seven of the inbreds at Iowa State, and Ben Duddleston developed four of the inbreds from Troyer Reid that fill six of the 20 inbred-parent slots at Purdue.
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The supreme lesson in Background of U.S. hybrid corn is that adaptedness was critical to popularity and to persistence of germplasm (Troyer, 1999). The Richey Lancaster cultivar would more likely persist as 8% of U.S. hybrid corn background than would a long-eared, corn-show oddity. I have added LAN below the line and RL to the LLE and LE bars now placed under Lancaster Sure Crop in Fig. 1. Richey Lancaster is nearly 9% of known U.S. hybrid corn background through Iowa inbred LAN and Ohio inbred OH40B. Lancaster Sure Crop per se is a little >4% of known U.S. hybrid corn background through Connecticut inbred C103. Lancaster Sure Crop in total is 13% of the documented U.S. hybrid corn background (Fig. 1).
Earnest W. Lindstrom
Earnest W. Lindstrom, academician and codeveloper with Dr. Jenkins of persistent Iowa inbreds IDT and LAN (LLE), was born of Swedish immigrant parents in Chicago in 1891. He received an A.B. degree from the University of Wisconsin in 1914, and earned the Ph.D. degree at Nebraska and Cornell University under Dr. R.A. Emerson in 1917. In World War I, he was a U.S. army officer (bomber ferry pilot) in France. Dr. Lindstrom returned to Wisconsin, joined the faculty of the Genetics Department, and did the first corn inbreeding there in 1920. In 1922, he joined the Iowa State faculty, where he became professor and head of the Genetics Department and vice-dean of the Graduate College. His genetics seminar was one of the most popular seminars on campus. He was a bulwark of sound counsel to many commercial hybrid corn breeders.
Dr. Lindstrom was graduate program advisor to Merle Jenkins, Bruce Griffing, Paul Harvey, Boyd Shank, and others. He routinely received precursors (probably at S3) of Dr. Jenkins' Iowa State inbreds. He finished inbreds IDT from Iodent Reid and LAN from Richey Lancaster. Both were important to Modern Iodent Inbreds (Lindstrom, 1931). Dr. Lindstrom published some 50 papers. He was a Fellow of the AAAS and a member of the Botanical Society of America, American Society of Naturalists, and the Genetics Society of America, where he served terms as Secretary, Vice President, and President (Lush, 1949).
LEAMING CORN
Henry A. Wallace developed inbred TEA from Illinois Two Ear (ITE) cultivar at Des Moines, IA, in about 1925. He later gave seed to Dr. F.D. Richey, who named it CI540 and to Dr. M.T. Jenkins, who named it Iowa ITE701 (Baker, 1984). In Jenkins' 1927 Iowa State Nursery Book row ITE 701, H.A. Wallace is listed as the source (A.R. Hallauer, 2002, personal communication). Illinois Two Ear cultivar had the highest 9-yr average yield at Urbana, IL, in 1927 (Mumford, 1928). Illinois Two Ear, a selection from Chester Leaming, was begun by Dr. Louie Smith, followed by Dr. C.M. Woodworth and Dr. F.L. Winter at the University of Illinois. The percentage of two-ear stalks started at 6.7% and was increased to as high as 85%, although the results were variable. It was recommended for silage because of difficult hand harvest (Mumford, 1925). Inbreds TEA, CI540, and Iowa ITE701 are synonyms. I have kept CI540 below the line and added TEA to the bar now placed under LEAMING. Inbred TEA (CI540) is also a component of Stiff Stalk Synthetic (Table 1).
Chester Leaming is nearly 4% of known U.S. hybrid corn background [half through inbred TEA (CI540) developed by Henry A. Wallace and half through inbred LE23 developed by Dr. Louie Smith at Illinois]. Mann Leaming is nearly 2% of known U.S. hybrid corn background through Illinois inbred L developed by Dr. Jim Holbert at Bloomington, IL. Ohio inbred OH07 developed by Glen Stringfield at Wooster, OH, is nearly 4% of known U.S. hybrid corn background through Pioneer inbred TEA (CI540) and Illinois inbred L (Fig. 1). Improved Leaming Corns, in total, are >5% of the documented U.S. hybrid corn background (Fig. 1).
Glen H. Stringfield
Mr. Glen H. Stringfield, developer of popular and persistent inbreds OH07 and OH43, was born (1893) and raised in extreme southeastern Nebraska near the small town of Stella. He graduated at the top of his baccalaureate class in 1924. He studied with Dr. T.A. Kiesselbach at Nebraska, joined the USDA staff at Ohio, and did graduate work for an M.S. degree at Ohio State in 1927, then a year of graduate work at Wisconsin before returning to Ohio. He developed popular Ohio inbreds OH07, OH26, OH43, and OH51A, among others. He developed Ohio inbred OH3167B in popular Stiff Stalk Synthetic. He retired in 1959 and joined DEKALB AgResearch, where he codeveloped popular hybrid DEKALB XL45, among others. He retired again in 1966, but continued consulting. He was a member of Alpha Zeta Agricultural Honorary and Sigma Xi Research Fraternity and a Fellow of the American Society of Agronomy and of the American Genetics Society. He died in 1975.
CORN BELT FEMALE COMPOSITE
Walter Vandeventer of Pioneer Hi-Bred at Princeton, IN, began work on Corn Belt Female Composite (FC) in 1951. He grew 22 proprietary inbreds used in female single-cross parents of Pioneer Hi-Bred commercial double crosses, and 46 mostly S3 inbreds self pollinated from crosses of the 22 proprietary inbreds in an isolated plot. Some entries were repeated up to eight times in the plot depending on degree of favor at the time. The background of the materials was predominantly Reid Yellow Dent, but Jarvis Golden Prolific, John Havel Long Ear, Krug Reid, Lancaster Sure Crop, and Midland Yellow Dent were also represented.
In 1952, seed from each 1951 entry was bulked in equal amounts and planted in a 0.2-ha (0.5-acre) isolated plot. Vandeventer selected plants for favorable agronomic traits. Selected ears were shelled, selected for kernel appearance, and tested for cold germination to further select for improved germination. In 1953, the selected ears from 1952 were yield tested per se, and remnant seed from the best performing ear-entries was used for breeding material by Vandeventer. The particular inbred from these materials that influences background was unusually low eared (Pioneer Hi-Bred International, 1952, 1953; B. Ambrose, 2001, personal communication). Female Composite is 3% of the documented U.S. hybrid corn background (Fig. 1).
DAWES CO., NB
Karl Kahl, Pioneer Hi-Bred district sales manager, collected seed of Dawes Co., NB open-pollinated cultivar from a farm near Mount Horeb, which is near Madison, WI. The farmer had brought the seed from Dawes County in extreme northwestern Nebraska. Karl delivered the seed to Murray Brawner at Princeton, IL, in the early 1960s. The cultivar was about 100 to 105 RM (days relative maturity) and had unusually soft grain texture. The endosperm type and kernel shape were intermediate between typical dent and gourd seed. It was another source of fertility restorer (Rf1) for Texas male sterile cytoplasm. Nebraska inbred N4 was developed from Dawes Co. Dent. Earl Collins of Pioneer Hi-Bred at Princeton, IL, developed the soft-textured, high-yielding Pioneer inbred, WM8, from Dawes Co. Dent, which is nearly 2% of the documented U.S. hybrid corn background (M. Brawner, 2001, personal communication; Fig. 1).
LONGFELLOW
Longfellow Flint originated near Byfield, MA, which is the location of the Longfellow family's original homestead. Mr. Henry Wadsworth Longfellow, poet and academician, left records of Longfellow Flint using the possessive case to signify the cultivar originated with him (Galinat, 1991). Longfellow was America's favorite writer in the 19th century. Among other styles, he wrote popular narrative poems. In The Song of Hiawatha, Part 13 Blessing of the cornfields, Longfellow uses the words corn and maize 18 times. He knew something about corn. Galinat (1991) states Longfellow Flint seems to be a yellow endosperm form of Rhode Island White Flint. Ears are 28 cm (11 in) long, 3.7 cm (1.5 in) in diameter, and have eight kernel rows on a white cob. Kernels are medium size, medium depth, and yellow to dark yellow in color. Stalks are about 2.1 m (7 ft) in height, medium diameter, and have few tillers. It flowers 70 d after emergence. Longfellow flint was recommended by the Maine, Massachusetts, Michigan, and New Hampshire Agricultural Experiment Stations in 1936 (Jenkins, 1936).
Perry Collins developed Pioneer inbred LF5 from Longfellow Flint at Algona, IA. He used the pedigree method, and selected for strong silk emergence at flowering and for other agronomic traits. The inbred was popular in the late 1950s. It contributed earliness, loose husks, yield, and harder kernel texture to 95 and 100 RM double-cross hybrids. Longfellow Flint cultivar is nearly 2% of the documented U.S. hybrid corn background (Fig. 1).
MIDLAND
Raymond Baker of Pioneer Hi-Bred observed the fast acceptance of hybrid corn in 1937 and asked Murray Brawner to obtain and increase seed lots of the more popular open-pollinated cultivars for inbreeding. Murray increased about 20 Agricultural Experiment Station recommended cultivars at Princeton, IL, in 1938. One of the cultivars was Midland, or MD DENT, Midland Yellow Dent, which was recommended by the Kansas, Missouri, and Oklahoma Agricultural Experiment Stations (Jenkins, 1936). Because of its late maturity, seed from the Midland increase was sent to Bill Landgren at Poseyville in extreme southern Indiana for inbreeding (M. Brawner, 2001, personal communication).
Midland Yellow Dent was developed from a locally grown unnamed yellow corn cultivar by Mr. O.A. Rhodes of Columbus, KS, who selected for a certain plant and ear type. It was grown on his farm since 1894 and first attracted the attention of the Kansas Experiment Station in 1912. Midland Yellow Dent is described as a medium-late cultivar, requiring 120 to 125 d to mature. Ears are 24 to 25 cm (9.5 to 10 in) long and 17.8 cm (7 in) in circumference, tapering somewhat, with butts fairly well rounded, and tips usually well filled. Kernels are rather narrow and thick in proportion to their width, medium depth, and somewhat rounded at the crown. Indentation varies from a dimple to a wrinkle. Stalks are 2.4 to 2.7 m (8 to 9 ft) in height. It was superior to all other yellow cultivars in southeastern Kansas. Midland Yellow Dent usually produces corn if any is produced in Cherokee county (Anonymous, 1929).
The critical 2 yr in inbred development were S1 and S2 dry-land observation tests near Beatrice, NE, where the Midland entries stayed green and made corn. They were virtually the only survivors. The resulting inbred also had excellent root strength and poor cold test germination. It was in nearly all Pioneer 120 RM double crosses (B. Ambrose, S. Jensen, and B. Seifert, 2001, personal communication). Bill Landgren developed the Midland inbred that is nearly 2% of the documented U.S. hybrid corn background (Fig. 1).
PROLIFIC COMPOSITE SMPR
Cultivar SMPR, under Prolific Composite, is a newer source of genetic diversity (Smith et al., 1999). In SMPR, the S stands for stress selection; the M for Mankato, MN; and the PR for Prolific Composite. Dr. W.L. Brown developed Prolific Composite from nine prolific cultivars and two semiprolific hybrids. Argentine Pop and Mexican June cultivars are tropical; Carroway Prolific, Clark Yellow Dent, Jarvis Golden Prolific, Mosby Prolific, Neal Paymaster, Turkish Prolific Pop, and Whatley Prolific are southern, temperate cultivars. The two hybrids were adapted to central Iowa; the earliest inbred in the hybrids was a Pioneer/Minnesota inbred B164 derivative (Troyer and Brown, 1976, Troyer and Larkins, 1985).
Selection to develop SMPR was at twice normal plant density with 136 kg ha–1 (300 lb acre–1) of actual nitrogen at 44° N lat. I selected 11 cycles for earliness (5%) with the last six cycles also selected for stalk quality (36%)(Troyer and Larkins, 1985). The suffix S5 in SMPRS5 stands for the fifth cycle of stalk quality selection with 10 cycles of selection for earliness (Smith et al., 1999). Compared with Prolific Composite (also known as Iowa synthetic BS11), SMPR has 150 g kg–1 (15 points) lower grain moisture at harvest, 13 d earlier flowering, 30.7 cm (1 ft) shorter plant height, 3 d less silk delay, and 1380 kg ha–1 (22 bushels acre–1) more yield at normal plant densities. SMPR grows fast, flowers early, dries fast, and tolerates stress. SMPR germplasm was in two popular, early (100 to 105RM) Pioneer brand hybrids. Pioneer brand hybrid 3737 was their second most popular corn hybrid for 2 yr (Pioneer Hi-Bred International, 1987, 1988).
The two Iowa hybrids in Prolific Composite provided genes for adaptedness. Natural selection occurred under cooler temperatures, longer days, and shorter seasons. Materials were prolific, which helped reduce barrenness at higher plant densities. Human selection was for crowding and drought tolerance, for earlier flowering, and for better stalk quality. The materials had rare, needed traits for which the method selected. SMPR is about 0.3% of the documented U.S. hybrid corn background (Fig. 1).
COMPETITORS' HYBRIDS DEKALB 56
Charlie Gunn of Dekalb AgResearch developed hybrid Dekalb 56, first grown commercially in 1945. Its two-digit number indicated adaptation to Maturity Zone 0, the early corn company's earliest growing area. It dried fast, yielded well, and stood well. This most popular hybrid for Zone 0 sold more than 50000 bags yr–1 for 8 yr in its 23-yr period and totaled about 850000 bags. Dekalb 56 contained one inbred each from Golden King, Osterland Reid, and Western Plowman cultivars (W. Holdridge, 1993, personal communication). The fourth inbred (no. 7), with unknown background to DEKALB, was obtained from Dr. Jim Holbert of Funk Brothers Seed Company. Its background was Krug Reid (D.R. Sywassink, 2001, personal communication). Perry Collins of Pioneer Hi-Bred at Algona, IA, self-pollinated DEKALB 56 to develop a popular inbred that is nearly 2% of the documented U.S. hybrid corn background (Fig. 1).
COMPETITORS' HYBRIDS SRS303
Cultivar SRS 303 was a newer source of genetic diversity in the 1980s (Smith et al., 1999). Very little is known about the background of SRS 303. I am told it was a hybrid that stood well in central Indiana and Ohio in a year when severe stalk rot epidemics and widespread down corn occurred in the early 1960s (J.H. Weatherspoon, 1970, personal communication). SRS 303 descendants account for nearly 2% of the documented U.S. hybrid corn background (Fig. 1).
COMPETITORS' HYBRIDS DDRF101
Steve Noble of Pioneer Hi-Bred at Johnston, IA, self pollinated competitors' hybrid Dockendorf 101 (DDRF101) that led to an inbred in 1960. Dockendorf 101 was tested from 1955 through 1961 in the Iowa Corn Yield Test, where it showed average performance. The new inbred had unusual ability in hybrids to adjust its ear size to a wide range of plant densities. Competitor hybrid DDRF 101 is about 1% of U.S. hybrid corn background (Fig. 1; W.B. Ambrose, 2001, personal communication).
COMPETITORS' HYBRIDS M3204
Bob Seifert of Pioneer Hi-Bred at Union City, TN, crossed Mississippi double-cross hybrid 204 (M3204) to Connecticut inbred C103 for breeding material in 1953. Mississippi hybrid 204, (MP448/T204) (MP424/GT112), was a large, midseason, yellow endosperm hybrid adapted to central Mississippi. It was developed by Dr. Robert Eckhardt, USDA breeder at Mississippi State. The hybrid's background by inbred is 1/4 Yellow Jellicorse; 1/8 Florida Laguna, 1/16 Reid Yellow Dent, 1/16 Clarage; 1/4 Kyle Long Season; and 1/8 Whatley Prolific/Creole Yellow Flint, 1/16 Cuban Yellow Flint, and 1/16 Garrick Prolific, respectively (P. Williams and N. Widstrom, 2002, personal communication).
Seifert's objective was to improve the adaptation of C103 to the South. He developed a ‘C103 type’ inbred that yielded well in hybrids even when stressed by lack of moisture or sunlight. Competitor hybrid M3204 is about 0.3% of the documented U.S. hybrid corn background (Fig. 1).
COMPETITORS' HYBRIDS HT4
After World War II, Holland (the Netherlands) looked at corn as a possible new crop. Imported corn was expensive. News of the success of hybrid corn from the USA was exciting. The D.J.Van der Have Company joined the Holland food industry in starting a foundation for the promotion of corn. As a first step, Ton Hendriksen of D.J. Van Der Have visited the USA on a fact-finding tour in 1949. He visited universities to obtain breeding sources, and also received top-cross seed for testing in Holland. Ton also visited Pioneer Hi-Bred at Johnston, IA, where an alliance for seed research and sales in Europe was eventually organized.
A 5-ha (12-acre) corn nursery was established near Rilland, Holland, where inbred HT4 was developed. Inbred HT4's expanded name is HaTo 4. Ha stands for Van der Have, and To stands for top cross. One of the top cross entries obtained on Ton's tour of universities was the source of inbred HT4. We do not yet know its pedigree. Inbred HT4 test crosses were made at Pioneer Hi-Bred near Johnston, IA, then yield tested in Holland (F. de Wolff and D. Glas, 2001, personal communication). Curtis Norskog of Pioneer Hi-Bred at Willmar, MN, crossed Pioneer inbred HT4 to Minnesota inbred A509 and developed a popular inbred in the early 1970s. Inbred HT4 descendants are about 0.3% of the documented background of U.S. hybrid corn (Fig. 1).
FOREIGN HOWE'S ALBERTA FLINT
Howe's Alberta Flint (PI 214194) was a common corn grown in Alberta, Canada. Bill Landgren of Pioneer Hi-Bred at Willmar, MN, used it as a source of earliness to adapt later inbreds to the northern U.S. Corn Belt. Howe's Alberta Flint ears are 15 to 18 cm (6 to 7 in) long with 8 to 10 kernel rows on white cobs. Kernel color is yellow. Plant height is 99 cm (40 in), and ear height is 20 cm (8 in). It flowers 39 d after emergence. Growth under cool conditions (spring vigor) is excellent. It is very susceptible to common smut, and is extremely early flowering, very short and tillers profusely. It often has two and sometimes three ears on the main stem and one ear on some tillers when grown at moderate densities (Troyer and Hallauer, 1968). Howe's Alberta Flint is about 0.3% of the documented U.S. hybrid corn background (Fig. 1).
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Many breeders of corn inbreds wanted local adaptation, which had been important for open-pollinated cultivars. Some breeders chose rare (unpopular) cultivars, hoping in vain for more heterosis. Wellhausen (1956) touted Mexican corns to improve U.S. Corn Belt corn, and significant effort with Mexican corns followed. Among this miscellany, germplasm from the five popular, more widely adapted cultivars persisted and eventually prevailed at 87% of known background because of their adaptedness (Fig. 1). Quality of germplasm (better acclimated to the present environment) prevailed over genetic diversity of germplasm. We are improving the adaptedness of a tropical crop to the temperate U.S. Corn Belt climate.
What do these five open-pollinated cultivars have in common? They were popular and widely grown as cultivars. Jenkins (1936) lists about 375 recommendations for 181 open-pollinated cultivars from 48 states to average two states recommended per cultivar. One hundred twenty-two cultivars were recommended in only one state, 21 in two states, 12 in three states, nine in four states, and seven cultivars were recommended in five states. What about improved strains or extended families? Reid Yellow Dent goes from 21 to 26 recommendations (add Black, Funk, Osterland, Strain 176A, and Troyer). Leaming goes from seven to 11 (add Canada, Early, Improved, and Somerset). Northwestern Dent goes from nine to 12 (add parent Bloody Butcher in three states). Lancaster Sure Crop goes from five to six (add Sure Crop) recommendations. These five popular cultivars were better adapted to the U.S. Corn Belt climate and more widely grown than lesser-recommended open-pollinated cultivars.
How popular were they? Reid Yellow Dent and its derivatives were once grown on 75% of U.S. Corn Belt acreage (Anonymous, 1930; Wing, 1923). In the late 1920s and early 1930s, white-endosperm corn hectarage was diminishing rapidly (lack of vitamin A for feed), and hybrid corn was still experimental. Jugenheimer (1955) states Reid Yellow Dent, developed in the last third of the nineteenth century, was highly productive, widely adapted, and extensively grown. It won Grand Champion 10 Ears at the World's Fair in Chicago in 1893. Leaming Corn was grown more than all other yellow-endosperm cultivars combined before Reid Yellow Dent was developed (Troyer, 1931). This would be >25% of the total in the last quarter of the 19th century when half the corn grown was white. Leaming Corn won a bronze medal at the World's Fair in Paris in 1878. Minnesota 13 was recommended in 15 states, and moved growing ear corn northward 80 km (50 miles) in the USA in a decade (Hays, 1904; Jenkins, 1936). Northwestern Dent was popular in northwestern USA (Idaho and Montana), northern USA (North Dakota, Minnesota, and Michigan), and at higher elevations (Arizona and Utah).
Natural selection and human (artificial) selection are effectively adapting the corn crop to the U.S. Corn Belt climate. Darwin (1859)( 1868) devoted two chapters to natural selection in Origin of Species, and two chapters to human (artificial) selection in Variation of plants and animals under domestication. Darwin's principles of selection and adaptation (survival of the fittest) during open-pollinated corn's selection in the U.S. Corn Belt followed by the hybrid seed corn companies' goal to provide more widely adapted hybrids (more weatherproof, more dependable); readily explain the preeminence (87%) of the five popular, open-pollinated cultivars in the known background of U.S. hybrid corn (Troyer, 1996).
Human (Artificial) Selection
Corn is widely adapted, totally dependent on humans for survival, and easily mated during the day. These factors make corn the ideal crop for successful selection by humans. Transformation of the corn ear is governed by five major mapped genes (Doebley et al., 1990). As wild corn became domesticated, humans selected nonshattering, larger ears for easier harvest and storage. As the ears became larger, lack of seed dispersal caused the need for further domestication. Larger ears and domestication were mutually supportive. Movement from tropic to temperate areas required selection for earlier maturity. After European colonization and westward expansion, land ownership made land a limited resource, causing increased yield per unit area of land to become important. Seed corn people typically selected for more good ears in moderate plant densities as a way to obtain more good ears. Choice seed was sold on the ear; better ears commanded higher prices. Single-eared plants were preferred for hand harvest. Human selection was for higher yield, lower kernel moisture for safer storage, and better standing ability (Troyer, 1999, 2004).
Scientific plant breeding began a century ago with recognition of the individual plant as the unit of selection and use of the progeny test (Hays, 1903; Troyer, 2003). The pedigree method (Hayes and Johnson, 1939) selects individual plants of known pedigree for desirable traits from two or more entities into one inbred. It is the workhorse of corn breeding. Outstanding, popular Iowa inbreds B14, B37, and B73 were developed by recurrent selection with early testing (Hallauer et al., 1983), which involves intercrossing superior segregates based on test-cross yields of unfinished inbreds. Richey (1945) accurately predicted the majority of yield improvements would be made by cumulative selection, which is the repeated use of the pedigree method using superior inbreds as source materials. It's a form of recurrent selection with late testing. It requires less time and less yield testing (less money) between successive improved inbreds than early testing methods (Troyer, 1990, 1996, 2000).
Because so much progress came from so few, so old, and so popular cultivars, adaptedness to the present conditions of life is evidently more important than genetic diversity to increase yields. As long as higher yield means more progeny (seeds) and means progeny more likely to survive to leave progeny, evolutionary biologists would surely agree. Natural selection and human (artificial) selection have increased adaptedness that increased yield. Again, U.S. corn breeders are adapting a tropical crop to a temperate environment.
What traits are critical for yield selection? The U.S. Corn Belt has longer daylengths, cooler minimum temperatures, more drought, and shorter seasons than southern Mexico (18°N lat), where corn originated. Successful new diverse background sources will exhibit adaptation to these needs. Selection for adaptation to these conditions and to improved agronomic production practices will continue to increase yield (Darwin, 1859, 1868; Troyer and Rosenbrook, 1983; Troyer, 1999, 2000).
Natural Selection
Charles Darwin and A.R. Wallace (Darwin and Wallace, 1858; Wallace, 1858) independently concluded that natural selection (sometimes described as survival of the fittest) was the chief cause of evolution of species after reading the Malthusian theory. Natural selection of wild corn was largely a matter of adaptation to environmental factors (daylength, temperature, and rainfall) for survival (Galinat 1977, 1988). Development and sale of open-pollinated cultivars emphasized local adaptation (natural selection). Buy local seed! An open-pollinated cultivar was necessarily widely adapted before it was widely grown. Its genes for adaptedness were garnered by natural selection based on climate and soils and by human (artificial) selection based on personal preference (Troyer, 1999, 2004).
Corn has adapted to many climates. Corn was first domesticated in 8000 to 5000 BC in tropical (18°N lat) south-central or southwestern Mexico (Goodman, 1988). During a 4000- to 7000-yr period, corn became adapted farther north to harsher temperate climates to reach what is now Arizona and New Mexico. Then, corn slowly worked its way north and east from river valley to river valley until reaching higher-rainfall areas. It reached St. Louis in about AD 200, southeastern USA in about AD 600, the Great Plains in about AD 700, and southern Ontario in about AD 1000. It became a food staple in the southeast USA in about AD 900 (Troyer, 2004). During American westward expansion, corn and the U.S. Corn Belt moved northwest. The top corn-producing states in 1838 were Tennessee, Kentucky, and Virginia, respectively. Forty years later, after selection of 750 newer, earlier flowering, more drought-tolerant cultivars, the top producing states were Iowa, Illinois, and Missouri (Montgomery, 1916). Corn adapted.
Is the U.S. Corn Belt climate changing? Great concern exists about the increase in global temperatures since 1900. Many atmospheric scientists believe the increase is linked to human-produced carbon dioxide (via fossil fuels) in the atmosphere. Carbon dioxide, methane, water vapor, and nitrous oxide trap heat within the earth's atmosphere and thereby produce warmer air temperatures. Ultraviolet rays from the sun penetrate the atmosphere, but infrared rays from the earth's surface cannot escape the atmosphere—the greenhouse effect (McGraw-Hill, 2002).
Since 1900, the amount of carbon dioxide and methane in the earth's atmosphere has increased 25%. During the same period, mean global temperatures have increased about 0.5°C (0.9°F). A rise in temperature is expected to alter global air and ocean circulation patterns, which will alter climates differently in different regions. Many species of mountain plants have shifted to higher elevations in the Swiss Alps at rates of up to 4 m (13 ft) per decade. In the USA, total precipitation has increased, but is delivered in fewer, more extreme events making floods (and possibly droughts) more likely (McGraw-Hill, 2002). Natural selection and human (artificial) selection will continue to be effective in adapting corn to changing climates.
Food Production
Science devoted a special issue to obesity (7 Feb. 2003, Vol. 299, no. 5608). The lead editorial states U.S. food is so overproduced and so overmarketed that most adults—of all ages, incomes, educational levels, and census categories—are overweight (Nestle, 2003). It appears our food intake is limited only by each individual's willpower. This is proof of the effectiveness of U.S. plant breeding and agronomic production research. Hallelujah! We have delayed the Malthusian prophesy another century.
Thomas Robert Malthus graduated with honors in mathematics from Cambridge in 1788. He took holy orders the same year, but avoided work as a clergyman because of a speech impediment. He became a history of economics professor. He determined that human population increases in a geometrical ratio while food supply increases in an arithmetical ratio; therefore, wars or disease will need to reduce population unless number of children is limited. He became embroiled in utopian vs. pessimistic views of population increase. Malthus' first essay on population (Malthus, 1798) was 19 chapters and exceeded 50000 words. It literally caused reduced spending on social welfare in England. Between visits to several countries to collect more data, he wrote a total of seven editions. With time, he softened some of his harshest conclusions, but still recommended checks on population (Encyclopædia Britannica, 1983; Himmelfarb, 1960). The Malthusian prophecy will be pertinent as long as people have children and eat food.
United States corn production has increased from zero about 3000 yr ago, to 25.4 million Mg [1 billion (1 x 109) bushels] annually in the 1870s, to 76 million Mg [3 billion (3 x 109) bushels] annually in the 1950s, to 150 million Mg [6 billion (6 x 109) bushels] annually in the 1970s, and to more than 229 million Mg [9 billion (9 x 109) bushels] annually for the past 7 yr. Since hybrid corn, average U.S. corn production has increased 176 million Mg [7 billion (7 x 109) bushels] while reducing total hectarage 20% because corn yields increased more than 6271 kg ha–1 (100 bushels acre–1; Fig. 2) .
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Nature (6 Feb. 2003) included a news feature entitled "A Dying Breed" with the headline "Public-Sector Research into Classical Crop Breeding is Withering, Supplanted by Sexier High-Tech Methods." But without breeders' expertise, molecular-genetic approaches might never bear fruit (Knight, 2003). The same fewer breeders trend is happening in commercial crop breeding. This has apparently already reduced food production. Our highest average U.S. corn yield, 8691 kg ha–1 (138.6 bushels acre–1), occurred in 1994 before transgenic corn hybrids. Herbicide-tolerant corn (not transgenic) was first grown in 1992. Transgenic, Bt, insect-resistant corn was grown on 202429 ha (500000 acres) in 1996. Adding herbicide tolerance and insect resistance traits delays or replaces adding genetic gain for yield by corn breeders.
Since 1950, the USA has never gone so long (8 yr) without an increase in record yield of corn (Fig. 2). The average interval between record U.S. average corn yields for this period (1950–1994) is 2.1 yr. This recent delay in record yield increase is probably because of more emphasis on insect and herbicide resistance and less emphasis on yield per unit area. The regression of U.S. average corn yield on years for the decade (1994–2003) since transgenic corn is about two-thirds (b = 85.4 vs. 125.4 kg ha–1 or 1.4 vs. 2.0 bushels acre–1) of that for the period (1950–1994) when conventional breeders bred all hybrid corn. Direct selection for yield is more effective than indirect selection for yield (countering weeds and insects). Reducing weeds and insects at the expense of additional yield is poor economics for the farmer and reduces food production.
Originally, seed corn companies were developed by farmers for farmers. Successful, profitable, seed corn companies respond to farmers' needs. Higher yields help farmers by increasing efficiency that reduces the cost of production, which helps farmers offset inflation. Farmers buy nearly all the seed. Through a lifetime of experience, they expect newer hybrids to yield more. Warning labels should be required on newer hybrids that don't yield more. Higher yields lower the cost of corn for users (e.g., feeders, industrial processors). Higher yields delay the Malthusian prophecy. We expect to feed more people in this, the 21st century, than the total number of people that have previously existed on our planet. How are we going to do that? Higher yields will help. Meanwhile, farmers' cost of production will continue to be the fundamental factor affecting the demand for corn and for corn growing (Troyer and Mascia, 1999).
There is no love sincerer than the love of food.—George Bernard Shaw
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ACKNOWLEDGMENTS |
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Received for publication May 25, 2003.
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