The purpose of this study was to investigate the effect of variations in climatic factors
such as vernalization periods, minimum- and maximum temperatures and rainfall on
the expression of host plant resistance to RWASA1 (original biotype) and RWASA2
(newly identified biotype) in the eastern Free State of South Africa between 2003 and
2006. Climatic records indicate above-average temperatures and reduced rainfall
occurred in the Eastern Free State in 2003 to 2005 probably contributing to
widespread RWA damage on dryland wheat crops. Greenhouse experiments
confirmed that vernalization did not alter RWA plant resistance ranking of wheat
entries. However, infestation did produce significant damage by RWASA2 on Elands,
Gariep and Limpopo but not on CItr 2401 (containing Dn-4 and another unidentified
Dn-gene) and Halt (Dn-4). Resistance rating to RWASA1 of Halt, Komati and
Matlabas in greenhouse tests at 18°C/12°C, 22°C/16°C and 26°C/22°C shifted to
less resistant- or susceptible categories and changed the ranking of SST 966 as
temperature increased. Also, RWASA2 ratings at increased temperature shifted Halt
to a more resistant category and changed rankings of Komati and SST 399. Komati,
Matlabas, SST 966 or SST 399 did not express any host plant resistance to
RWASA2 through leaf area or leaf roll and chlorosis supporting the susceptible
ratings that were given to the same varieties in the visual screening test. Seeddressing
in AMMI results for 2003 to 2006 were able to increase yields under higheryielding
conditions in seasons when moisture- and heat stress occured and the yield
performance of cultivars was stabilized irrespective of whether they contained
genetic resistance to RWA. Identifying new RWA resistance donors provide an
excellent opportunity to exploit novel germplasm with potential new genetic variance
for RWA resistance, as well as other beneficial traits such as drought-tolerance.
Three germplasm pools were evaluated for this purpose. Twenty-one entries from the
Stillwater, Oklahoma/SGI RWA resistance pool expressed resistance against
RWASA2 in the seedling test and where generally well adapted to local conditions.
Seedling evaluation of the CIMMYT pool revealed twenty entries with acceptable
resistance to RWASA2 though field adaptability particularly to biotic stress was
occasionally lacking. Twenty entries from the Iranian pool were resistant to RWASA2
though unadapted for resistance to stripe rust; Puccinia striiformis Westend f.sp tritici
Eriks., occurring in the Eastern Free State.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ufs/oai:etd.uovs.ac.za:etd-04082009-140505 |
| Date | 08 April 2009 |
| Creators | Lindeque, Robert Crowther |
| Contributors | Dr VL Tolmay, Prof MT Labuschagne |
| 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-04082009-140505/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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