Corn Breeding: Lessons From the Past
Inbreeding, Hybrid Vigor, and Hybrid Corn
At about the same time the corn shows were peaking in popularity, in the northeast United States two researchers were experimenting with controlled pollinations in corn. Their findings would soon cause a remarkable change in the corn culture of North America. Both Edward East at the Connecticut Experiment Station and George Shull at the Carnegie Experiment Station on Long Island had begun to self-pollinate corn.
When a plant from an open-pollinated variety is self-pollinated, all the progeny resemble that plant, although they all differ from each other and from the parent plant to some extent. If one of the progeny plants is self-pollinated, the new progeny again differ from each other and from the parent plant, but the degree of the difference is not as great as occurred after the first self-pollination. If this process is repeated about seven times, then a plant known as an inbred is produced. An inbred is a pure-breeding strain of corn. This means that if an inbred is self-pollinated, all of the progeny will be genetically identical to each other and to the inbred parent.
This process of repeated self-pollinations is known as inbreeding. Inbreeding corn results in loss of vigor (Figure 9).
A hybrid developed by crossing two inbreds is known as a single-cross hybrid. As is true for an inbred, all plants of a single-cross hybrid are genetically identical to each other. The productivity of a hybrid depends on the relationship between the two inbreds. A hybrid produced by crossing two inbreds developed from different but equally productive open-pollinated varieties usually will produce a more vigorous hybrid than one produced by crossing two inbreds from the same open-pollinated variety.
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