Breeding systems
A breeder has as the objective to breed improved cultivars with better characteristics.
Conventional breeding
Most varieties are derived from crosses between established cultivars. Often two parents are selected in such a way that the two parents are complementary in the traits they possess.
In a conventional breeding programme various methods are used: 1) pedigree method, 2) back-crossing, 3) recurrent selection and 4) progeny testing.
A breeder will rarely use only one specific breeding system but generally uses a synthesis of various systems.
CONVENTIONAL BREEDING PROGRAMME----BREEDING METHODS-----
Wild and primitive potato species
New traits are often found in wild and primitive potato species. Since the wild and primitive species often also possess a number of undesired traits, which can only be removed with time-consuming and expensive long back-crossing programmes, it is often desirable to select parental material that is as close (e.g. S. andigenum) as possible to the cultivated potato cultivars.
Tuberosum cultivar and new andigenum introduction
Genetic engineering
For the years to come the processing industry is asking for varieties that have the same processing qualities as e.g. the varieties Bintje and Russet Burbank, but with better resistance to insects, viruses, Late blight based on a polygenic genetic system.
Classical potato breeding methods have some fundamental limitations.
New methods such as: (1) induction of somaclonal variation with selection in vivo or in vitro, (2)somatic hybridization where intact parental genotypes and cytoplasm are combined and (3) gene transfer by genetic engineering (transformation of existing varieties) are subjects of research. Gene transfer is most appealing and successes have been reported for resistance to Colorado beetle (based on BT-genes) and resistance to PVY.
With this new methods there also are various limitations:
- new biotypes of the insect that are resistant to the BT used may develop
- gene transfer for traits controlled by dominant genes is more likely to be successful than for
traits controlled by polygenic systems e.g. Late blight.
- with gene transfer more changes take place than just the introduction of a single gene. A
modified variety is not exactly the same as the original. The new gene has to fit into
a balanced system.
- in several countries genetic engineering is not socially accepted
It is most likely that these new breeding methods still have to be followed by "conventional" selection and breeding methods.
With genetic engineering genes that control certain wanted characteristics are introduced into existing cultivars.
Gene transfer