In agriculture and gardening, hybrid seed is produced by cross-pollinated plants. Hybrid seed production is predominant in modern agriculture and home gardening. It is one of the main contributors to the dramatic rise in agricultural output during the last half of the 20th century. The alternatives to hybridization are open pollination and clonal propogation.
All of the hybrid seeds planted by the farmer will produce similar plants, while the seeds of the next generation from those hybrids will not consistently have the desired characteristics. Controlled hybrids provide very uniform characteristics because they are produced by crossing two inbred strains. Elite inbred strains are used that express well-documented and consistent phenotypes (such as high crop yield) that are relatively good for inbred plants.
Hybrids are chosen to improve the characteristics of the resulting plants, such as better yield, greater uniformity, improved color, disease resistance.
An important factor is the heterosis or combining ability of the parent plants. Crossing any particular pair of inbred strains may or may not result in superior offspring. The parent strains used are therefore carefully chosen so as to achieve the uniformity that comes from the uniformity of the parents, and the superior performance that comes from heterosis.
In the US, experimental agriculture stations in the 1920s investigated the hybrid crops, and by the 1930s farmers had widely adopted the first hybrid maize.