Innovators in the Advent of Hybrid Corn
Crop Insights written by Lance Gibson, DuPont Pioneer Agronomy and Product Knowledge Training Manager
- Few other scientific developments have had greater impact on increasing food supplies available to the world’s population than the development of hybrid corn.
- James Reid and George Krug were two farmer breeders who made substantial contributions to corn improvement in the early part of the 20th Century.
- Scientific inquiries led by academics Edward East and George Shull laid the groundwork for hybrid corn production.
- Herbert Hayes started inbreeding corn in 1909 and developed the inbreds used in the first practical corn hybrid.
- No person was more important to commercialization and farmer acceptance of hybrid corn than Henry A. Wallace, the founder of what has become DuPont Pioneer.
- The Hi-Bred Corn Company was organized and incorporated in Iowa on April 20, 1926. This was the first strictly hybrid seed company and the predecessor of DuPont Pioneer.
The development and wide-scale adoption of hybrid crops is one of humankind’s greatest achievements resulting in a multi-fold productivity increase over pre-hybrid genetics. Few other scientific developments have had greater impact on increasing the food supplies available to the world’s population than has the development of hybrid corn. The pure-line breeding methods used to create inbred parents for hybrids were applied to variety development for self-pollinating species allowing the transformation of a couple of minor crops, soybean and rapeseed (the predecessor to canola), into world leaders. These methods also made vast contributions to the improvement of wheat and other cereal grains. The discovery and use of male sterility systems brought hybridization to many other crops with spectacular success. Seed companies and public research programs continue to actively seek new ways of hybridizing crops by overcoming the natural limitations to self-pollination. The use of hybrids has seen a steady rate of increase over many decades and will continue to expand in the future.
This Crop Insights on the discovery, development, and commercialization of hybrid corn is intended to provide awareness of some of the trailblazers who contributed to the discovery and adoption of the hybrid breeding system that continues to support the development of innovative Pioneer® brand crop genetics. Buildings on the DuPont Pioneer campus in Johnston, Iowa are named for many of these historic innovators.
Early History of Corn Production
A discussion of how corn genetics were selected and passed between seasons before hybrids were introduced is required to fully understand the history of hybrid corn development. Based on archaeological and DNA evidence, maize was domesticated in Mexico sometime between 6,000 and 10,000 years ago.
Figure 1. Teosinte (Zea mays subsp. Mexicana), an ancestor of modern corn native to Mexico and Central America.
Prehistoric people collected the wild ancestors of today’s corn for large kernels that would provide them sustenance for their daily activities. At some point, they discovered that kernels could be planted back to the soil for annual harvest. Each year, they would select seeds of favored types for planting in the next season. Over the millennia, this annual selection slowly changed corn into the crop we recognize today.
Over time, indigenous farmers in the Americas developed methods of composite breeding and mass selection where seeds from good ears or plants were saved each year for planting in the next season. As long as it was kept isolated from other corn types, the seed produced from a distinct strain would be true to type from one generation to the next. Many distinct corn types and strains were developed using these methods.
As corn evolved into an easily grown and productive crop, it became a major component of the diet and was spread throughout the Americas. The American natives shared corn with new arrivals to North America from Europe. The colonists brought the crops of their birthplaces, such as wheat, oats, barley, and rye, with them. While they favored the traditional crops for direct consumption, they quickly learned that corn made excellent feed for livestock. As immigrants to North America moved into the central U.S., corn became the lead crop, eventually expanding to a peak of over 113 million acres planted in 1932. Explorers of the Americas from Europe returned home with corn seeds and distributed the crop all over the world.
Immigrants to the American colonies and farmers around the world refined the indigenous corn selection processes to develop many farmer-bred open-pollinated varieties. The best varieties were traded locally, spread with mass migrations during settlement of the interior lands of North America, and widely sold with the introduction of the postal service and catalog sales. The peak of farmer corn breeding occurred in the late 1800s and early 1900s when grower associations and land grant colleges established “corn shows” for exhibiting “perfect” corn ears selected by farmers. These contests were hosted at the county, state, national, and international levels and brought high esteem and wide-spread acclaim to the winners.
Important Farmer Breeders
Of the many farmer breeders, two stand out for their substantial contributions to corn improvement. The first is James Reid of Illinois who improved “Reid Yellow Dent” using mass selection from 1866 to 1910. The second is George Krug, who bred his own open-pollinated variety from 1906 until the early 1930s.
Reid Yellow Dent was an open-pollinated variety first introduced to Illinois by Robert Reid. His son, James, improved the variety by carefully selecting ears based on agronomic, ear, and kernel traits. Agronomic selection was placed on medium maturity (100-110 days), adaptability to Corn Belt conditions, vigorous plant growth, tall and leafy plants, and mature, dry seed at harvest time. Ears were selected for medium size (9 to 10 inches long and 7 to 8 inches around); 18 to 22 tightly-aligned kernel rows; a small, dark-red cob; slight tapering from butt to tip; filling of the ears over the tip; and a small shank to ease hand husking. Reid desired solid, deep, narrow- to medium-width, smooth kernels with bright yellow color and dented, light-colored crown. Both Robert and James gave seed to their neighbors to ensure the purity of Reid Yellow Dent by limiting pollen contamination from other strains of corn.
Figure 2. Reid Yellow Dent, an open-pollinated variety used widely up until the adoption of hybrid corn in the 1930s.
Fifty years of selection and promotion advanced Reid Yellow Dent into the dominant U.S. variety. Other farmer breeders throughout the U.S. began selecting from Reid Yellow Dent in the late 1800s to create their own versions. It was adapted to nearly every state and comprised up to 75% of U.S. corn acres. University experiment stations began creating Reid Yellow Dent varieties in the early 1900s. Inbreds developed from several Reid Yellow Dent varieties became parents of the first commercial hybrids.
George Krug, a corn farmer from Woodford County in central Illinois, developed the most improved strain of Reid corn. He began experimenting with seed corn to improve production on his 100-acre farm. Krug combined a Nebraska strain of Reid’s Yellow Dent corn with Iowa Gold Mine to make his own strain. At first, he didn’t realize how good his corn was as he hadn’t entered it in a show or tested it against other varieties. With the encouragement of his local agent, Krug entered his variety in the county farm bureau yield test beginning in 1919. Ears of Krug’s corn were uneven in size and kernel shape, yet it produced the best yield among 118 entries in 1920 and 1921. It yielded ten bushels an acre better than the most touted ‘show type’ corn. Krug spent an additional 10 years improving his variety and it was fervently desired by farmers throughout the U.S. It won the Iowa corn yield tests in 1926 and became the most widely-used open-pollinated corn in many areas. Krug’s corn seed was even shipped for growing in South Africa, Romania, and Argentina.
Dawn of Scientific Breeding
Application of science to agriculture in the U.S. began with the passing of the Morrill Act of 1862, which created the framework for land-grant colleges in each state. The Hatch Act of 1887 further authorized the establishment of an agricultural experiment station, affiliated with each land grant college of agriculture. At first, college professors concentrated on selecting the best corn to use as seed and joined in promoting, organizing, and judging corn shows. Initial efforts at improving corn genetics were slow, but started to gain traction in the early 1900s. By 1910, corn shows were very popular in the U.S. Corn Belt. Farmers would enter ten of their best ears of corn and judges rated them on appearance. It was thought that the best looking corn would also produce the best yields. By the early 1900s, breeders and extension educators were promoting selection techniques considered to be an improvement over traditional farmer methods.
Some in the breeding and scientific community began to question the relationship between selection of show ears and improvements in corn yield. Observations over many years and data collected by the U.S. Department of Agriculture showed corn yields were not improving. In response, agricultural colleges began sponsoring yield tests starting around 1915 for direct comparison of varieties under controlled conditions.
Figure 3. United States average corn yield, showing the lack of yield improvement up through the 1930s and dramatic gains during the hybrid corn era. (Source: USDA-NASS).
The corn yield tests and other research observations suggested mass selection was likely protecting the crop from yield declines and improving some minor agronomic characteristics, but was doing very little to improve productivity. Qualitative traits, such as kernel or cob color, could be readily selected but quantitative traits, such as yield, were not very responsive to these breeding efforts. Average corn yields in the U.S. had remained stagnant (at a little over 20 bu/acre) for nearly 70 years between passage of the Morrill Act and the early 1930s (Figure 3). The yield tests began to put attention on choosing corn for yield rather than selecting seed corn from the most beautiful ears.
Early Hybrid Corn Research
It was the basic scientific inquiries of academics Edward East and George Shull that brought hybrid corn to the scene. East and Shull individually initiated research on selfing individual corn plants to produce purified lines – East at Connecticut State College in New Haven and Shull at Cold Spring Harbor Laboratory on Long Island in New York. Their pursuits did not turn out as planned as they quickly discovered that just a couple generations of inbreeding resulted in plants with significantly less yield and vigor than the original parent. However, Shull crossed inbred lines he had created and made an interesting discovery. The hybrid offspring had growth superior to the inbred parents and had comparable or better yields and greater uniformity among plants than the varieties from which the inbreds were derived. He published a scientific paper on these results in 1908. Shull had observed the effects of heterosis in corn and began immediately applying it in further breeding investigations. In a paper published the next year, he outlined procedures that later became standard in hybrid corn breeding programs.
Both East and Shull had doubts about the practicality of corn hybrids for wide-scale use as inbred lines produced very little seed. East, in particular, thought the need to generate new seed each year and its cost would cancel the benefit of higher yields from hybrids. East’s students, Herbert Hayes and Donald Jones weren’t as negative toward the discovery and pushed forward in a quest to make hybrids feasible.
Hayes started inbreeding corn at Connecticut State College in 1909 and became a firm believer in the untapped potential of hybrid corn after harvesting 200 bushel-per-acre yields in consecutive years. He would go on to develop the inbreds used in the first practical corn hybrid, the Burr-Leaming double-cross hybrid. Hayes moved on to the University of Minnesota in 1915 as a small grain and corn breeder, contributing greatly to research on the most efficient procedures for breeding corn hybrids and training many plant breeders.
As a graduate student, Jones originated the idea that would eliminate low seed production of inbred lines as a limitation to the wider use of hybrid corn. He devised a scheme where he crossed two inbred lines to make one hybrid and two other distinct lines to create a second hybrid. He then used these two single-cross hybrids as parents to make a second generation, double-cross hybrid.
Jones began his research work at the Connecticut Agricultural Experiment Station in New Haven in 1914. By 1917, he found that the heterozygous single-crosses made suitable parents for field-scale seed production and the four-way, double-cross hybrids yielded about as much as the two-way, single crosses. The four-way crosses were more variable than single-cross hybrids, but much less so than open-pollinated varieties. Plentiful seed production made the scheme practical for field use. Over the next several decades, corn breeders improved seed production in inbred lines so that single-cross hybrids could be practically grown and sold by the 1950s.
Figure 4. Vintage poster showing crosses involved in creating a double-cross, or four-way cross, hybrid.
No person was more important to commercialization and farmer acceptance of hybrid corn than Henry A. Wallace, the founder of what has become DuPont Pioneer. He was one of a handful of people in the world who initially recognized the immense opportunities that could be gained by growing hybrid corn. Wallace began experimenting with corn in high school with the goal of developing a hybrid that would produce high grain yield. At age 16, he field-tested prize-winning show corn against corn less beautiful in appearance. The results challenged conventional thinking at the time by demonstrating there was no relationship between yield and appearance of the ears.
Wallace attended Iowa State College, graduating in 1910. While in college, he became fascinated with the relatively new science of genetics. After graduation, Wallace began working on corn-breeding experiments and started breeding hybrid corn in 1920 after visiting Edward East and Donald Jones at the Connecticut Agricultural Experiment Station. The mathematically inclined Wallace taught himself statistics and applied it to his experiments. By 1923, he had produced a high-yielding hybrid he called Copper Cross. In 1924, it became the first hybrid to win the gold medal in the Iowa Corn Yield Contest conducted by Iowa State.
Figure 5. Henry Wallace inspecting corn ears.
Convinced that hybrid corn had a bright future, Wallace continued to produce and market small quantities of hybrid seed. He also promoted hybrid corn through frequent writings in his family’s magazine, Wallaces Farmer, a top agriculture periodical. Continued success of his hybrids convinced Wallace to expand operations and bring new human and financial resources into the business. With the help of several friends, the Hi-Bred Corn Company was organized and incorporated in Iowa on April 20, 1926. This was the first strictly hybrid seed company and the predecessor of DuPont Pioneer. Wallace was selected as U.S. Secretary of Agriculture by Franklin D. Roosevelt in 1932 and elected Vice President of the United States in 1940.
Figure 6. Pioneer® hybrid 307, a double cross hybrid sold from 1936 until 1963.
Hybrid adoption was slow during the first decade after their commercial introduction by Henry Wallace in 1924. Farmers weren’t used to purchasing new seed each year, the seed was expensive to produce, and it was in short supply. The situation began to quickly change in the mid-1930s. Yield tests and farmer experience during the “Dust Bowl” years from 1934 to 1940 demonstrated hybrids to be vastly superior to open-pollinated varieties under severe drought. The first widespread plantings of hybrid corn began in 1935 when 6% of Iowa corn acreage was planted to hybrids. Once farmers had solid evidence of the benefits of hybrid corn, the transition away from open-pollinated varieties was astonishingly rapid. By 1942, nearly all Iowa acres were planted to hybrid corn. Adoption of the new hybrids quickly spread around the world. The high yields, stress tolerance, and pest resistance of hybrids made growing corn feasible in areas where it hadn't been grown before.
Expansion of Hybridization and Related Innovations
Hybrids have been so superior in agronomics, yield, and return on investment for furthering genetic gain that they’ve been sought after in most major crops. Discovery and application of male sterility systems resulted in commercial introduction of hybrids for sorghum in 1956, sunflower in 1959, and canola in 1989. Hybrids were immediately embraced by farmers for all three crops. But, widespread commercialization of hybrids has yet to be realized for some crops with flower morphological constraints that limit cross pollination. Hybrids may never be feasible for crops that are highly predisposed to self-pollination, such as soybean.
Several key developments beyond the uncovering and exploitation of heterosis were vitally important to the initial adoption of hybrid crops. Yield tests established by state agricultural experiment stations were essential to proving the superior qualities of hybrids to farmers. The experimental design principles and statistical techniques developed by R.A. Fisher provided powerful analytical tools used in quantifying genetic improvements. New laboratory and breeding techniques resulted in effective screening of desirable traits and combination of these traits into improved parent lines.
Before closing out this retrospective on hybrid corn, there are three additional scientists worthy of note for their enduring contributions to the development of hybrid corn and study of corn genetics. Each of these has a building named after them on the DuPont Pioneer campus.
Figure 7. George Washington Carver
George Washington Carver
George Washington Carver, the great scientist and inventor widely credited with development and promotion of peanuts and other alternatives to cotton production in the southern U.S. had a personal relationship with a young Henry A. Wallace. Carver was a student and Wallace’s father was a professor at Iowa State College in Ames. The young Wallace often went on plant collecting trips with Carver in fields around Ames. Wallace credited Carver with introducing him to the “mysteries of plant fertilization” and deepening his appreciation of plants “in a way he could never forget.”
Rollins Emerson is known as the father of maize genetics. He began his career at the University of Nebraska in 1899 and took a leave of absence in 1910 to pursue additional studies with Edward East, who had recently moved from Connecticut State College to Harvard University. He returned to Nebraska and began studying trait heritability and quantitative genetics in corn. He continued this work at Cornell University in 1914 as professor and head of the department of plant breeding until he retired in 1942. Emerson’s laboratory trained many of the world’s foremost geneticists of the twentieth century.
Figure 8. Barbara McClintock
Barbara McClintock, one of Emerson’s students developed the technique for visualizing corn chromosomes under a microscope and used microscopy to demonstrate many fundamental genetic ideas. She produced the first genetic map for corn, linking chromosomal regions to physical traits. McClintock was awarded the 1983 Nobel Prize in Physiology or Medicine for the discovery of genetic transposition, the ability of genes to change position on chromosomes.