TRANSFER OF ALIEN GENETIC VARIATION IN PLANT BREEDING


George Fedak
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.




References


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.