Corn Breeding: Lessons From the Past
Corn Grain Yields, 1930 to Today
The national average corn grain yield in the United States began to increase steadily in the 1940s (Figure 11). In the most recent decade, the average yield was 125 bushels per acre, nearly five times greater than 70 years before. Several studies conducted by universities have indicated that much of this improved yield was the result of improved genetics; that is, it occurred because farmers were planting improved varieties of corn developed through plant breeding. Greater use of fertilizer, more and better herbicides, improved soil tillage, and other altered production practices also contributed to the increased yields.
The yield advantage of a single-cross hybrid produced by crossing two inbreds developed from two different open-pollinated varieties over the average of the two open-pollinated varieties varies greatly depending upon the open-pollinated varieties that are chosen. It may be as great as 100%, but in many instances will be less. But improvement in average yields from 1930 to 2002 was 400%. In addition to hybrid vigor, genetic improvements were made. Today’s single-cross hybrids yield more than the single-cross hybrids of 70 years ago. Also, public corn breeders have developed many varieties (often called populations or synthetics) that are superior to the open-pollinated varieties that were popular before the introduction of hybrids.
Why were corn breeders in the mid- and late-20th century able to make such substantial genetic improvements for grain yield, whereas no increase in yields was realized from 1870 to 1930? The development of single-cross hybrids was partly the answer. But two other factors contributed.
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