Wheat (Triticum aestivum L.) is widely cultivated over large areas and is an
important food crop worldwide. Wheat is extensively used during the production
of many different types of foods. Wheat rusts (leaf, stem and stripe rust) are
important foliar diseases of wheat worldwide, causing large losses and damage
to the wheat industry. The ability of these rust pathogens to change and be
dispersed over long distances pose a continual global threat. Annually millions
around the world are spent on fungicides in an attempt to control wheat rusts.
Resistant cultivars have proven to be the most effective, economical and
environmentally friendly form of rust control. Although many resistant cultivars
have been developed historically, a need for more durable resistance exists.
The application of molecular markers and marker-assisted selection (MAS)
strategies in breeding programmes can support plant breeders in accomplishing
pyramiding of several rust resistant genes into new cultivars.
The aim of this study was to pyramid seven rust resistant genes/QTL (leaf,
stripe and stem rust) into a single genotype using five SSR, three STS and two
AFLP markers. The study focused on wheat genes applicable to the local wheat
industry and markers used and/or developed in South African breeding
programmes. In this study four bread wheat cultivars or lines (AvocetYrsp,
Blade, CSLr19-149-299 and Kariega) were used as parental sources of five
resistance genes (Sr2, Sr26, YrSp, Lr19 and Lr34) and two QTL (QYr.sgi-7D
and QYr.sgi-2B). Selection after each cross was done using a MAS approach
with SSR and STS markers linked to the different resistant genes/QTL. The
study was conducted over a two year period, involving the development of two
different sets of F1 offspring and one double cross generation from a series of
directional crosses.
Before crosses were made, the presence of the expected rust resistance genes
was confirmed in the parental lines using specific SSR, STS and AFLP markers.
The SSR and STS markers amplified the expected allele sizes in the parental
lines, except for the unexpected detection of the Lr34 gene in AvocetYrSp. Results indicated that the Sr2 marker was not consistently present in Blade,
suggesting the Blade cultivar was heterogeneous for Sr2. The AFLP markers
linked to the YrSp resistance gene did not detect differences between the
parental lines and were excluded from further experiments. The F1 generations
were screened with one SSR or STS marker each to identify successful
crosses. Genotyping of the F1 generations indicated than on average, 85.5% of
the tested F1âs were true hybrids. Phenotypic screening was done on the
parental lines and F1 individuals for the three rust types and confirmed the
presence of the expected genes in the parental lines as well as selected F1
individuals.
A total of 900 individuals of the double cross generation were screened with five
SSR and three STS markers associated with resistance genes and QTL to
identify whether gene pyramiding within a single genotype was successful. The
number of individual plants of the double cross population containing markers
linked to the desired resistance gene(s)/QTL ranged from two individuals
containing none of the markers to three individuals containing all eight markers.
The three individuals containing eight markers confirmed the presence of
markers associated to the presence of the four single genes (Sr2, Sr26, Lr19
and Lr34) and two QTL (QYr.sgi-7D and QYr.sgi-2B.1). Due to the inefficiency
of the AFLP markers, the presence of the seventh gene (YrSp) could not be
confirmed on genotypic level. The future uses of the developed rust resistance
gene pyramided lines of this study are countless. The use of these lines in
combating the continual threat of wheat rusts in some manner should be helpful
in future.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ufs/oai:etd.uovs.ac.za:etd-02052009-140213 |
| Date | 05 February 2009 |
| Creators | Sydenham, Scott Lloyd |
| Contributors | Dr L Herselman, Prof ZA Pretorius |
| Publisher | University of the Free State |
| Source Sets | South African National ETD Portal |
| Language | en-uk |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.uovs.ac.za//theses/available/etd-02052009-140213/restricted/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University Free State or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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