Corn Hybrids
Corn Breeding in the 20th Century
By L.W. Kannenberg, Professor Emeritus, Department of Plant Agriculture, University of Guelph

The first corn hybrids for farm use were produced in the 1920s, but until the 1940s most farmers still were growing open-pollinated (OP) varieties. In very short-season areas, the OPs were flints because of their tolerance to cool, wet spring conditions and requirement for fewer heat units to reach harvestable maturity. But the most corn acreage by far was planted to OPs from a new race of corn, Corn Belt Dent, that arose somewhat serendipitously during the early decades of the 1800s.

During that period, farmers in the mid-maturity areas of the U.S. favored growing OPs of the Southern Dent race because of their high-yield potential. But often, seed quality was poor because of immaturity at harvest, resulting in poor stands in the following spring. Farmers would replant gaps with early maturing OPs of the Northern Flint race.

Natural crossing between the Southern Dent and Northern Flint OPs resulted in “inter-varietal” hybrids that farmers quickly noted were superior to either of the parents. Farmer selection in Corn Belt Dent created hundreds of OP varieties, some of which became widely disseminated because of their preeminence in the popular corn shows of the late 19th and early 20th centuries.

One famous OP, Minnesota 13, was developed near St. Paul around 1900. It was the highest yielding (48.5 bu/ac) of eight varieties tested over a 21-year period (1906-1926) by Charles Zavitz at the Ontario Agricultural College (OAC). The seed was obtained annually from Northrup King and Company in Minneapolis and was marketed in Ontario as University No. 13. The other varieties in Zavitz’s study included Genesee Valley, Salzer’s North Dakota, Compton’s Early, two strains of White Cap Yellow Dent and two strains of Longfellow. Minnesota 13 eventually became an important source of inbred lines for the hybrid corn industry, as did a few other OPs, especially Reid’s Yellow Dent and Lancaster Sure Crop.

In the 1930s, the OPs grown in southwestern Ontario included Canada Golden Glow, Wisconsin #7 (Silver King), Bailey, Ontario Golden Glow, White Cap Yellow Dent, Canada Leaming and Burr Leaming. Some Essex County growers that produced strains of these were P. Adams, J. Ainslie, D. Bondy, N. Cazabon, B. Cohoe, F. Dahl, A. Iler, C. Lypps, G. Newman, S. Olsen, R. Pinkerton, H. Sellars, F. Smith, and G. Smith.

Annual per-acre grain yields in the U.S. and Canada showed virtually no improvement until the advent of hybrid corn. The history of hybrid corn begins in the early 1900s with Dr. G.H. Shull, a geneticist at the Carnegie Institution of Washington, a private research institution in Cold Spring Harbor, New York. Gregor Mendel’s seminal research on the bases of heredity, published in 1866, had been rediscovered in 1900 and interest in the emerging science of genetics increased dramatically.

Shull’s approach was to study the effects of inbreeding and subsequent cross-fertilization in corn. In 1909, he published “A Pure Line Method of Corn Breeding” in which he outlined – with remarkable insight – the basics of breeding hybrid corn. At about the same time, E.M. East also was studying the effects of inbreeding and cross fertilization in corn at the Connecticut Agricultural Experiment Station. East’s results agreed with Shull’s, but East pointed out that producing hybrids was not commercially feasible because of seed production costs.

Indeed, the first inbreds had poor vigor and seed yields were low. Because the seed parent of a single cross hybrid is an inbred line, hybrid production costs would be prohibitive. Then in 1918, D.F. Jones, a colleague of East’s, resolved the problem by suggesting that two single-cross hybrids could be crossed to produce a double-cross hybrid, thus having a relatively high yielding single-cross hybrid as the female parent for hybrid seed production.

Although double crosses were the prevalent hybrid type in industry until the 1960s, the first commercial hybrid, Copper Cross, was a single cross produced in Iowa under contract for Henry A. Wallace in 1923, using an inbred from East Leaming as the female parent and a Bloody Butcher inbred as the male. The seed sold for $1 a pound. Wallace founded “Hi-Bred Corn Company” which subsequently became Pioneer Hi-Bred. Several other corn companies also began hybrid production in the 1920s.

Only 0.4 per cent of the U.S. corn acreage was planted to hybrids in 1934. By 1944, this had ballooned to 59 per cent and, in the Corn Belt, 90 per cent. By 1956, all of the Corn Belt and 90 per cent of the U.S. corn land was in hybrids. In Ontario, the first extensive tests of hybrids were made in 1938, and by 1941, about 75 per cent of the corn acreage in southwestern Ontario was in hybrids. Since 1960, all of the field corn in the U.S. and Canada has been, with rare exception, hybrid. The dramatic shift from OPs to hybrids occurred because hybrids were not only higher yielding, but they stood up better, were more tolerant to stresses (drought, diseases, insects), and – because of their standability and greater uniformity – they were better suited for mechanical corn picking. As well, the grain quality was better. The early hybrids were by no means perfect, but they were a major improvement over the OPs.

By the 1960s, recycling (i.e., selection of new inbreds from crosses of the best inbreds of previous generations) had produced inbreds with sufficient seed yield and stability to serve as seed parents for commercial production of single cross hybrids. In the 1960s and 1970s, three-way hybrids – in which the seed parent is a single cross and the male an inbred – were also important, especially in short-season areas where the parent lines had not yet reached the yield levels of their longer-seasoned counterparts. The improved performance of today’s inbreds has resulted in single crosses being the norm in all maturity zones. Single crosses are more uniform than three-ways and double crosses and, on average, yield, respectively, about five- to 10-per cent more.

Most inbreds in the early years of hybrid corn were produced by public corn breeders. Greater emphasis on line development by commercial companies since the 1950s increased the proportion of private lines. Today, only a few new lines have public origin. The growth in private corn breeding has been phenomenal. An industry survey in 1989 showed an increase of 100 Ph.D. corn breeders in the U.S. from 1982 to 1989. A 1994 survey of U.S. plant breeding research by Dr. Kenneth J. Frey from Iowa State University showed that about 510 Science Person Years (SYs) were devoted to corn breeding in private industry, compared to 35 SYs in the public sector. The bottom line is that there are more Ph.D. corn breeders in any of the large corn breeding companies than all the public corn breeders combined in the U.S. and Canada.

As in the U.S., the number of public corn breeding programs in Canada has deceased considerably. At one time there were corn breeders at the federal research stations in Lethbridge, Morden, Brandon, Ottawa, Harrow, and St. Jean, plus breeders at the University of Manitoba, Macdonald College and University of Guelph. Today only the programs at Guelph and Ottawa survive. The role of the public corn breeders in the U.S. and Canada has shifted from being the primary developer of inbred lines for the hybrid corn industry to niche breeding. This includes line development for short-season areas (under 2,800 OCHUs) which do not receive adequate industry breeding emphasis because of the relatively small market size; germplasm enhancement so as to broaden the elite but very narrow genetic base that industry uses; development of germplasm with special characteristics such as ear mold resistance, cold tolerance, food quality, etc.

The public sector also makes important contributions to basic research in corn breeding and the education of future corn breeders. The reduction in university corn breeding programs coupled with the diversion of graduate students to the exciting world of biotechnology has resulted in a deficit of new corn breeders for industry. Perhaps industry, with its large base of scientists, resources and facilities, will have to become proactive in the training of future generations of corn breeders.

Corn yields during the OP years were essentially static. With the advent of double-cross hybrids, yields in the U.S. increased at the rate of 1.1 bu/ac per year. The era of the single cross hybrid has seen this rate almost double to 2.06 bu/ac per year, resulting in average yields that in most years now are more than twice the highest yields of the double cross period.

Provincial yields in Ontario parallel the U.S. situation. For example, our highest yield in the double-cross era was 64 bu/ac in 1959; in 1998, Ontario averaged about 129 bu/ac, and this figure includes corn yields from inherently lower yielding, short-season areas for which grain corn hybrids were not yet available in earlier years. Several studies comparing corn hybrids from different eras have shown that at least one per cent gain in yield per year can be attributed to improvement through breeding.

Most hybrids produced in North America have pedigrees tracing back to a very few old publicly developed inbred lines. Corn breeders are concerned that the continual reworking of this constricted genetic base might diminish breeding progress. In recent years, public and industry breeders in the U.S. have collaborated in a project for germplasm enhancement of maize, U.S. GEM. The GEM project evaluates germplasm from the Americas for its potential to contribute to the hybrid corn industry, and to provide the germplasm in forms that can be introgressed into industry breeding programs. Biotechnology also could play an important role in meaningful diversification of the germplasm base. For example, molecular fingerprinting could be used to identify germplasm that could contribute useful genes and gene complexes to our current breeding materials.

The latter part of the 20th century has seen two related phenomena in the corn breeding industry. The first began in the mid-1970s with the purchase of seed companies by chemical and pharmaceutical multinationals. Consolidation in the industry continues unabated. The driving force is the second phenomenon: the emergence and first benefits of biotechnology. The effect on the industry of a growing negative public perception of the first wave of biotech products such as Bt and Roundup Ready is now being played out. The next wave, the relatively inexpensive production of pharmaceuticals via transgenic crops, should prove more attractive to the consumer.

One concern I have – although I have been assured otherwise – is that the breeding effort to convert standard inbreds to their transgenic versions may dilute the effort devoted to traditional inbred development, which may, in the short term, slow the rate of hybrid improvement. However, my guess is, that corn producers can look forward to a steady increase in hybrid performance through the next millennium along with a myriad of specialty and designer corns from which to choose.

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