|This article does not cite any references or sources. (December 2009)|
In hybrid seed production, the crosses are specific and controlled. The advantage of growing hybrid seed compared to inbred lines comes from heterosis. To produce hybrid seed, elite inbred varieties are crossed with well-documented and consistent phenotypes (such as yield) and the resulting hybrid seed is collected.
Another factor that is important in hybrid seed production is the combining ability of the parent plants. Although two elite inbred parent plant varieties may produce the highest yields of their crop, it does not necessarily mean that crossing these inbreds will result in the highest yielding hybrid. The level of heterosis that the parents will generate in the resultant seed is called "combining ability." Higher combining ability between the parents results in increased performance in the resulting hybrid seed.
Hybrids are bred to improve the characteristics of the resulting plants, such as better yield, greater uniformity, improved color, disease resistance, and so forth. Today, hybrid seed production is predominant in agriculture and home gardening, and is one of the main contributing factors to the dramatic rise in agricultural output during the last half of the 20th century. In the US, the commercial market was launched in the 1920s, with the first hybrid maize. All of the hybrid seeds planted by the farmer will be the same hybrid while the seeds from the hybrids planted will not consistently have the desired characteristics. This is why hybrid seed is constantly repurchased by growers for each planting season.