Stripe rust, caused by the fungus Puccinia striiformis f. sp. tritici, is one of the most important
diseases of bread wheat (Triticum aestivum). In recent years the disease has reached a global
distribution, also causing significant crop losses in South Africa since 1996. The deployment of
disease resistant cultivars is recognised as an effective approach to minimise crop losses without the
higher input costs associated with the application fungicides. The need for new sources of durable
resistance has become apparent with the regular changes in the pathogen population and the
emergence of more virulent races. Quantitative trait loci (QTL) mapping is a powerful tool for
unravelling the genetic components responsible for disease resistance. For the purpose of this study,
two cultivars have been identified with complete adult plant resistance (APR) to stripe rust.
Previously, the South African spring wheat Kariega has been studied and the Lr34/Yr18/Pm38 gene
and two major QTL, QYr.sgi-2B and QYr.sgi-4A, were identified in a Kariega X Avocet S doubled
haploid (DH) mapping population. Cappelle-Desprez is an old European winter wheat for which
resistance genes/QTL have been postulated. The objective of this study was to dissect the APR for
stripe rust in these cultivars using a QTL mapping approach. The Kariega QTL were further
characterised by increasing the DNA marker density in a more targeted approach. Additional simple
sequence repeat (SSR) markers were incorporated in the genetic map and expressed sequence tag
(EST) markers were developed for screening by means of single-strand conformation polymorphism
(SSCP) analysis. The conversion of EST and Diversity Arrays Technology (DArT) markers to
sequence tagged site (STS) markers were investigated to allow for high-throughput screening. In
addition, selected SSR and DArT-STS markers were screened in a large Kariega x Avocet S F2
mapping population to improve the genetic map resolution in the QTL intervals. The QYr.sgi-2B and
QYr.sgi-4A intervals have been delimited to 6.1 and 16.2 cM respectively, in the F2 mapping
population with the aid of recombinant mapping. Resistance displayed by Cappelle-Desprez was
studied in a Palmiet x Yr16DH70 recombinant inbred line (RIL) mapping population. The breeding line
Yr16DH70, a Cappelle-Desprez derivative, is a more suitable parent in a spring wheat background.
SSR and DArT markers were typed in the population. QTL were identified, and up to 75.2% of the
phenotypic variance could be accounted for. A major QTL, QYr.ufs-2A, explaining up to 53.2% of the
phenotypic variance was identified on chromosome 2A. The presence of the Yr16 gene on
chromosome 2D was confirmed (QYr.ufs-2D) and additional minor QTL were detected on
chromosomes 5B (QYr.ufs-5B) and 6D (QYr.ufs-6D). A minor QTL, QYr.ufs-4B was derived from
Palmiet. Stripe rust resistance QTL from Kariega and Cappelle-Desprez provide valuable sources of
resistance in adapted, spring wheat backgrounds to South African breeders. Improved
characterisation of the QTL has led to the identification of QTL-associated markers, allowing for more
efficient selection in marker-assisted breeding schemes, and it also paves the way for map-based
cloning.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ufs/oai:etd.uovs.ac.za:etd-05272013-110046 |
| Date | 27 May 2013 |
| Creators | Agenbag, Gloudi |
| Contributors | Dr LA Boyd, Prof ZA Pretorius, Dr R Prins |
| 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-05272013-110046/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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