For most of the 20th century, hybridization was the main plant breeding method used by professionals.
Additional steps were added to make sure that improved strains of plants could be reproduced consistently. First, plants were self-pollinated or inbred for multiple generations to develop uniformity in the particular characteristics desired.
Then the uniform inbred plants were used as parents to cross-pollinate plants with other desirable characteristics. Because the two parent plant strains were uniform, they passed on these uniform characteristics reliably every time the parents were cross pollinated. This crossing of distinctly different parents also produced hybrid vigor and greater productivity.
This hybrid method required numerous generations of selection and back crossing when only one characteristic, such as disease resistance, was wanted from one parent. Crossing was limited to plants between one species or a closely related species. If no gene for disease resistance was found in cultivated or wild populations of the species, it was not possible to develop resistant plants.
During the past 20 years, techniques for transferring a single gene from a totally unrelated species by a process known as gene splicing has made dramatically rapid progress possible.
Many major crops such cotton, soybeans and corn are grown from varieties that have resistance to almost every major insect and disease. Strains that are resistant to weed killers are also widely used. This has not only increased yields but has reduced production costs and environmental impacts.
Gene splicing is not widely used for ornamental plants because the costs are not justified by potential sales. However, the development of tissue culture propagation or multiplication has had dramatic effects on ornamental plant breeding.
Now crosses can be made without concern for uniformity of seed production. A single improved plant can be increased to hundreds of thousands using tissue culture. This is the primary method now used for development of new fruits and ornamental plant varieties. Hybridization is still the most widely used method for developing new vegetable varieties.
Since gardeners prefer to buy started plants rather than seeds for ornamental plants, it does not matter whether the plant was grown from seed or tissue culture.
