TRANSFER OF ALIEN GENETIC VARIATION IN PLANT BREEDING
Plant Research Centre, Agriculture Canada, Ottawa, Ontario,
Canada, K1A OC6
Conventional plant breeding programs have been highly successful in all crops producing a steady stream of new improved cultivars. Thus these are elite genetic entities that combine the currently best available combinations of yield with tolerance to biotic and abiotic stresses and value-added traits. One of the immediate deleterious effects of a wide cross is the dilution of this elite germplasm which then will require numerous backcross generations to restore it.
Considering the immediate deleterious effects of wide crosses they are undertaken to introduce traits that are currently lacking in the primary gene pools of crop plants. Such traits include resistance/tolerance in wheat to fungal head blight caused by Fusarium, to Barley Yellow Dwarf Virus and to the wheat curled mite. Urgent requirements in barley include resistance/tolerance to the leaf spotting root rot complex caused by Helminthosporium and resistance to a new race of stem rust. In addition, cereal crops in temperate climatic zones can all benefit from additional genetic variability for such abiotic stresses as cold, heat drought and salinity.
There are several hundred species of wild relatives of crop plants in the tribe Triticeae that carry most of all of the above mentioned desirable traits but their transfer requires meticulous manipulations. The initial production of hybrids is accomplished by hormonal treatments of the maternal parents and embryo rescue on steadily improving media. Hybrids or derived amphiploids are repeatedly backcrossed to ideally produce a complete series of alien chromosome addition lines. Recombination is then induced between the critical chromosome addition lines and a crop plant chromosome. Recombination can be induced by callus culture, use of mutants of meiotic pairing control genes or suppressors of such genes.
Existing RFLP maps of various crops and species specific probes employing in situ hybridization techniques can now effectively be used to detect the size and site of interaction of alien chromosome segments. Additional manipulations are often required to reduce the size of such segments while retaining the traits in question. A simplified version of the RFLP technique, the RAPD-PCR method employing random or specific primers has been effectively employed to provide tags for integrated disease resistance genes. Such tags should prove to be amenable to improving the efficiency of selection for plant breeding purposes. Examples of the above manipulations from ongoing programs will be illustrated and discussed.
Fenner G, Chong J, Levesque M, Molnar S, Fedak G, 1993, Identification of a RAPD marker linked to the oat stem rust gene Pg3. Theor Appl Genet (in press).
Kim NS, Whalan EDP, Fedak G, Armstrong K, 1992, Identification of a Triticeae -Lophopyrum noncompensating translocation line and detection of Lophopyrum DNA using a wheatgrass specific molecular probe. Genome 35, 541-544.