Items from the South Africa.

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, and J.E. Snyman.


Triticale breeding. [p. 85]

In 2004, one of our top yielding cultivars (Tobie) became susceptible to a new leaf rust race and, in 2005, to a new stem rust race. In 2006, more than 90% of our germ plasm were susceptible to one or both races. The best combined resistance comes from a local cross of which the parentage includes both local cultivars/lines and CIMMYT germ plasm. The line is being multiplied for release in 2008 and has the pedigree IBIS/7/HARE 212/3/Champlain/Aronde 68//VPM/Moisson/4/Juanillo 100/5/Andas "S"/6/Durum wheat/Balbo//BOK"S"/3/Andas "S"//TJ/BGL "S".


Wheat recurrent mass selection. [p. 85]

Recurrent mass selection based on the Ms3 gene for dominant male sterility and hydroponic culture of cut wheat spikes was continued. In this breeding scheme, female and male plants are handled differently. Each year F1 seedlings are screened for resistance to a mixture of leaf and stem rust pathotypes. Selected female (male sterile) plants are used directly in crosses and the male component is field planted and selected. Superior F6 populations are then used as male parents in the crossing block. Single-seed descent steps have been integrated into the program, making it possible to rapidly (two seasons) advance from the F1 to the F5. In 2006, approximately 10,500 F1 were tested for seedling resistance to an inoculum mix of eight leaf rust and six stem rust pathotypes. About 3,200 (50% female and 50% male) resistant F1 plants were planted for crosses and single-seed descent. The female group was randomly pollinated with 100 field selected (2005) F6 lines to produce about 50,000 F1 seeds. A total of 959 F4 and 1,401 F6 lines were planted. An additional 110 senior trial selections (1­3 localities) and 34 elite trial entries (five localities) were tested. Following selection of the 2005 F6 population for agrotype, rust resistance and mixograph properties, 100 lines were used to compile an F7 nursery that was distributed to local breeding organizations in 2006. The same material was sent to Uganda to be evaluated for resistance to the new UG99 stem rust virulence.

To continue enriching the base population with resistance genes, recurrent backcrosses with the Lr19, Sr31/Lr26/Yr9/Pm8, and Lr21 genes were continued.

 

Genetic studies. [p. 85-86]

Homoeologous pairing induction experiments to remodel the alien translocation in four species-derived resistance sources were continued; these include (a) the Lr56/Yr38 translocation (6A; from Ae. sharonensis), (b) the Lr54/Yr37 translocation (2DL; from Ae. kotschyi), (c) the LrS15 translocation (1BL, Ae. peregrina), and (d) the LrS13/YrS13/SrS13 translocation (3AS, from Ae. speltoides). Test cross populations are being screened for recombinants making use of mapped microsatellite loci. Attempts to map (using the Inia 66 monosomics) leaf and stripe rust resistance genes (LrS20/YrS20) from Ae. neglecta and leaf rust resistance (Lrmac) from Ae. biuncialis were continued.

Disomic addition lines of Th. distichum chromosomes that appear to be involved in salt tolerance were produced in triticale and subsequently were used to develop two or more SCAR markers for each of the Thinopyrum target chromosomes. The markers could be employed to derive a panel of secondary Thinopyrum/triticale hybrids with different combinations of the critical chromosomes that were evaluated in tolerance tests. Results showed that single chromosomes had only minor effects on salt tolerance. Chromosomes 2J1d & 3J1d was the only combination of two chromosomes at a time to produce a notable effect whereas combinations 2J1d, 3J1d & 5J1d and 3J1d, 4J1d, and 5J1d resulted in high levels of tolerance comparable to that of the primary amphiploid.

Broad strategies to utilize the tolerance in cereals include (i) systematic production of Robertsonian translocations of the target J1d chromosomes to triticale /wheat homoeologues, (ii) production of plants with genomes 2n = 42 = AABBJ1/2dJ1/2 d that include the Thinopyrum target chromosomes, and (iii) production of octoploids with genomes 2n = 56=AABBRRJ1/2dJ1/2 d. To facilitate the latter attempts, pivotal genotypes were produced that are being used in molecular marker assisted backcrosses to produce the desired plants. An attempt also is being made to saturate the target chromosomes with anonymous markers that can be employed in attempts to further dissect the chromosomes and determine the locations of the genes involved.



Publications. [p. 86]

  • Heyns I, Groenewald E, Marais F, du Toit F, and Tolmay V. 2006. Chromosomal location of the Russian wheat aphid resistance gene, Dn5. Crop Sci 46:630-636.
  • Marais GF, McCallum B, and Marais AS. 2006. Leaf rust and stripe rust resistance genes derived from Aegilops sharonensis. Euphytica 149:373-380.