| Development of the aneuploid series and whole chromosome
substitution lines in the varieties Thatcher and Lemhi John UNRAU and John KUSPIRA Laboratory of Genetics and Plant Breeding, Univ. of Alberta, Edmonton, Alberta, Canada Once the aneuploid series have been established in certain varieties, genetic and breeding studies can be undertaken by making substitutions of whole chromosomes from other varieties. Seed of substitution lines having the chromosomal complement of the recipient variety with the exception of the substituted chromosome can be increased so that comparative replicated field trials can be conducted in which the genetic effects of the substituted chromosome can be studied on a population basis rather than on an individual plant basis. It is thus possible to use statistical methods in studying the results, making it possible to attribute quite accurately portions of the difference, in even quantitative characters, that are caused by the substituted chromosome. Very clear-cut genetic effects of chromosomes from the donor varieties Timstein, Thatcher and Hope in the genetic background of the variety Chinese Spring on such characters as yield, lodging resistance, earliness, protein content, etc., have been obtained in the last three years of testing. A detailed report will be published elsewhere. It should be possible, however, to get an even clearer picture of the genetic makeup and effects of the individual chromosomes if reciprocal chromosome substitution lines were developed in two varieties which had rather contrasting characteristics. For the purpose of studying more precisely the genetic control of the important characters of yield, earliness and quality, the aneuploid series have been developed in the variety Thatcher, a hard red spring variety, and the variety Lemhi, a soft white spring vatiety. The reciprocal whole chromosome substitution Iines are now being developed, but at least three more substitution backcrosses will be required before they are ready for field trials. Four other chromosome substitutions are fairly well along. These are of primary interest in the rust breeding projects. In the varieties Lemhi and Thatcher we are developing lines that have chromosome XX substituted with the homologous chromosome from the variety McMurachy. It has been shown that the gene for resistance to stem rust race 15b is carried by chromosome XX in this variety. The other two substitutions involve chromosome X of the variety Timstein. Rodenhiser and Seats have shown that two genes for resistance to a number of races of stem rust are located on chromosome X in the variety Timstein. We are well along in transferririg chromosome X from Timstein to the varieties Lemhi and Thatcher. Once the single substitutions have been completed, it is planned to combine thein into a single line, i.e. a line of Thatcher which has chromosomes XX from McMurachy and chromosomes X from Timstein. The same combination will be made in the variety Lemhi. Two further chromosome substitution Iines are being developed in the variety Thatcher. Chromosome IX is being substituted for the homologous chromosome from the winter wheat variety Kharkov MC22. Previous work has shown that Thatcher carries a gene or genes for winter habit of growth on chromosome XVIII. The gene or genes for spring habit on chromosome IX apparently are epistatic to those on chromosome XVIII. By replacing Thatcher IX by the homologous chromosome from a winter variety, it was expected that the substitution line so developed should have winter habit of growth. Results so far obtained indicate that the expectation was correct. The other substitution involves chromosome XVIII. As indicated, this, chromosome in Thatcher carries a gene or genes for winter habit of growth. It is to be replaced by chromosome XVIII from the very early variety Prelude. It is considered probable that this substitution may result in greater earliness in the variety Thatcher. |