Doctoral Degrees (Genetics)

Permanent URI for this collection

https://scholar.sun.ac.za/handle/10019.1/551

Browse

Browsing Doctoral Degrees (Genetics) by Subject "Aegilops L."

Now showing 1 - 1 of 1
  • Thumbnail Image
    Item
    Mapping and restructuring of an Ae. kotschyi derived translocation segment in common wheat
    (Stellenbosch : University of Stellenbosch, 2010-12) Heyns, I.C.; Marais, G. F.; University of Stellenbosch. Faculty of Agrisciences. Dept. of Genetics.
    ENGLISH ABSTRACT: The wild relatives are an important source of new genes for the genetic improvement of wheat. At Stellenbosch University the leaf and stripe rust resistance genes Lr54 and Yr37 were transferred from Aegilops kotschyi to chromosome 2DL of wheat. In an attempt to reduce the size of the whole-arm translocation on which the resistance genes occur, homoeologous pairing was induced between the wheat and corresponding Ae. kotschyi chromatin. The purpose of this study was to: (i) Evaluate the testcross progeny thus obtained; identify translocation recombinants that retained Lr54/Yr37 and to characterize these using molecular markers (ii) Test for the presence of genes for photoperiod insensitivity (Ppd) and reduced height (Rht) believed to be associated with the translocation (iii) Develop a SCAR marker for the most useful recombinant that could be recovered. Ten putative translocation recombinants were identified following the screening of 159 hemizygous testcross F1 plants with three microsatellite markers specific for chromosome arm 2DL. The recombinants were then characterized with another five microsatellite markers. Using the eight microsatellite markers the recombinants were ordered in two size categories with recombinant #74 being the shortest and having retained only proximal alien chromatin on 2DL. In addition to microsatellite markers, RAPDs, RGAs, AFLPs and SCAR markers were genetically mapped to the translocation and further resolved the recombinants into three size categories. In an attempt to find suitable markers linked to the shortest recombinant (#74) a polymorphic 410 bp AFLP fragment produced with the enzyme/selective nucleotide combination EcoRI – AAC/MseI – CAT, was converted into a dominant SCAR marker. In addition three microsatellite markers that mapped to recombinant #74 provided a useful recessive molecular marker system to detect Lr54/Yr37. Evaluation of the 10 recombinants with four 2DS-specific microsatellite markers revealed a large deletion of this chromosome arm in recombinant #74. This deletion may affect plant phenotypic characteristics and a strategy to replace the deleted region in recombinant #74 is proposed. To test for the presence of a gene for photoperiod insensitivity on the translocation, translocation-carriers plus controls were subjected to long and short day treatments, and the effect on time to flowering was studied. However, no evidence was found for the presence of such a gene. A height experiment to test for the presence of an Rht gene on the translocation confirmed its presence. This gene (designated H) appeared to be different from Rht8 on chromosome 2DS and was mapped on 2DL. While H does not occur in a chromosome region that corresponds with the location of Rht8, it does not rule out the possibility that they could be orthologous loci. Plant height data obtained for recombinant #74 suggested that H was lost through recombination in this particular recombinant. A greenhouse experiment suggested that the full-length translocation increased 100 kernel mass but had a detrimental effect on overall plant yield. Since a much shorter recombinant (#74) has been obtained, this will also have to be evaluated for associated effects. Such an evaluation needs to be done under commercial growing conditions and should involve the comparison of near-isogenic bulks with and without recombinant chromosome #74. The stripe rust resistance gene (Yr37) was mapped by screening hemizygous TF2 progeny of the 10 recombinants with Puccinia striiformis pathotype 6E22A+. Recombinant #74 retained both Lr54 and Yr37 and the two genes therefore occur towards the centromere.