ITEMS FROM SOUTH AFRICA


UNIVERSITY OF STELLENBOSCH

Department of Genetics, Stellenbosch 7600, South Africa

G.F. Marais, H.S. Roux, A.S. Marais, W.C. Botes, K.W. Pakendorf, and J.E. Snyman.

Triticale breeding. [p. 121]

A new stem rust pathotype appeared that is virulent on the recently released cultivar Tobie, and a new leaf rust pathotype, first seen in 2004, also has increased in frequency and caused particularly high infections in Bacchus. To counter this, we initiated a search for, and a crossing program with, further effective resistance genes. Results of the 2005 trials have shown that Tobie was the commercial cultivar with the best grain yield and hectoliter mass.

Wheat recurrent mass selection. [p. 121-122]

A commercial-scale, recurrent selection program is being conducted. Female plants (Ms3ms3) destined for crosses are selected as F1 seedlings, however, male parents are field tested and are not used in crosses until the F7. Approximately 10 500 F1 from the 2004 crossing block were tested for seedling resistance to an inoculum mix of eight leaf rust and six stem rust pathotypes. About 2,800 (50 % female and 50 % male) resistant plants were planted for crosses and single seed descent (SSD) and about 60,000 potentially different F1 seeds were produced. At the same time SSD inbreeding was initiated with seedling stem and leaf rust resistant F1 male plants. Following a sedimentation test, 500+ F4 SSD families (2003 crossing block) were derived and field planted for single plant selection. A total of 1692 F6 lines (2002 crossing block) were evaluated for agrotype, field disease resistance, and mixograph. The entire population was also screened (molecular marker) for presence of Sr24/Lr24. An additional 146 junior selections, 45 senior, and 16 elite trial entries were evaluated. To continue to enrich the base population with resistance genes, the development of two groups of material was continued. (i) Marker-assisted recurrent backcrosses targeting Lr19-149 and the Sr31/Lr26/Yr9/Pm8 complex (without the sticky dough characteristic) were initiated. (ii) Various other genes in diverse genetic backgrounds were backcrossed into adapted backgrounds in order to evaluate them for introduction into the base population.

 

Genetic studies. [p. 122]

(a) Transfers of leaf rust and stripe rust resistance genes Lr53/Yr35 (6BS; from T. turgidum subsp. dicoccoides), Lr54/Yr37 (2DL; from Ae. kotschyi) and Lr56/Yr38 (6A; from Ae. sharonensis) have been completed. The genes were distributed to local breeders and were entered into the South African, United States and Australian wheat germ plasm collections. (b) A gene with temporary designation LrS15 (from Ae. peregrina) appears to be located on 1AL, however, its location needs to be confirmed with microsatellites. (c) A leaf rust resistance gene from Ae. neglecta (temporary designation LrS20) has apparently been transferred to chromosome 3A of wheat. Genetic studies, RFLP and microsatellite analyses are being done in order to further characterize the resistance. (d) Attempts to transfer leaf and stripe rust resistance genes from a Ae. biuncialis group-3 addition chromosome produced a putative translocation that is being characterized.

Chromosomes 2J1d, 3J1d, 4J1d, 5J1d and 7J1d/7J2d of the indigenous grass, Th. distichum, appear to contribute to salt tolerance in this species. Disomic additions of chromosomes 3J1d, 5J1d and 7J2d and monosomic additions of 2J1d and 4J1d have been obtained. Using the addition stocks, RAPD fragments specific for each (except 7J1d) have been recovered and are being converted into SCAR markers. Testcross progenies from an attempt to induce translocations between 3J1d and corresponding triticale homoeologues are being screened for translocations making use of the newly developed markers.

Publications. [p. 122]