There are four major steps in the process of creating a new cultivar.
- Collect germplasm, the living genetic resources such as seeds or tissues that are maintained for the purpose of plant breeding, preservation, and other research uses. These are the resources that have promising characteristics, collected from various locations around the world. Plant breeders need to be observant and spot plants that exhibit the desired traits. For example, plant breeders may see a plant thriving along the roadside during a drought and want to obtain that trait.
Germplasm can be collected from:
- a. ecotype collections
- b. plant introductions from the USDA
- c. old cultivars (heterozygous population)
- d. experimental breeding populations
- e. native plants
2. The various collected specimens are planted and evaluated in a plant nursery. Breeders look for desired traits (color, growth habits, maturity stage, vigor, resistance, yield potential, and improved quality).
3. There are two main types of pollination involved in developing new cultivars; self pollinating and cross pollination. Some species are self pollinating including the vetches whereas other species like alfalfa, timothy, clovers, orchardgrass, tall fescue, ryegrass, bermudagrass, and corn are cross pollinated. Self pollination involves the transfer of pollen from an anther to the stigma of the same flower or a flower on the same plant. Cross pollination involves the transfer of pollen from an anther on one plant to a stigma in a flower on a different plant.
4. The techniques used in creating a new cultivar are: mass selection, recurrent selection, top crossing, and synthetic variety development.
In mass selection, the source population is examined and desirable plants or seed from those parent plants are selected. Sometimes old pastures, old yield trials, and plants from stressed or mismanaged environments are selected because they exhibit persistence in less-than-favorable conditions.
Recurrent selection involves following the desired traits in several generations of plants, harvesting the seeds and replanting and repeating the selection and replanting. Over multiple generations the desired traits that are true strengths will remain. This technique is used for those traits that are highly inheritable. For instance, some legumes have 2-5 genes involved in disease resistance so recurrent selection will single out those plants with this desired trait. There is little regard to location of the plants in the nursery for traits controlled by a few genes. But for traits controlled by a large number of genes, selection is made by carefully considering the location of the plants in the nursery. Often the nursery is divided into quandrants and the best plants are selected from each area. Selection may be made phenotypically, in which means selection is based on appearance. Selection may also be made genotypically, by evaluating the progeny or subsequent generations before selection is final. The best 3-8% plants are selected and the subsequent generation will have more plants that exhibit the desired trait. After a few generations the desired trait is common.
Top cross techniques incorporate one trait into an otherwise desirable variety. A donor population surrounds the recipient population and then the plants are backcrossed.
Another technique is synthetic variety development. Thousands of promising plants are grown in a nursery. After observations, 20-150 desirable plants are selected and crossed in isolation. Each is harvested individually. Genotypic evaluation is used and the progeny are tested in various locations and environments. The results of the progeny tests are used to recombine the parents.
