Wheat is the biggest winter cereal crop in South Africa and the second largest cereal to
feed the population of South Africa. The population of South Africa grows with
approximately one million people a year. Consistent wheat production is necessary for
food security and is therefore of extreme agricultural and economic significance. Future
production increases depend on the ability to improve, or at least maintain, the rate of
increase to feed the population. The study was undertaken to investigate genetic
improvement (genetic advance) in wheat by various statistical methods of analysis. This
was done to determine the most suitable procedure to evaluate genetic improvement in
the three wheat production areas of South Africa, namely the Western Cape province,
the Free State province and the irrigation areas. The second objective of this study was
to demonstrate the trend of yield and the two quality traits [HLM (hectolitre mass) and
protein content] over 16 years (1995-2010) by various statistical techniques. The third
objective was to compare the AMMI (additive main effects and multiplicative interaction)
and the GGE (genotype plus genotype-by-environment interaction) analyses in
assessing genotype-by-environment interaction (GEI) for yield and the two quality traits.
The fourth objective was to study the relationship among wheat grain yield and the two
quality traits by various statistical techniques. Linear regression (TRET) and various
variance component methods were investigated to determine genetic advance. The
recommended method of determining genetic advance in this study is TRET. In the
Western Cape elite trials TRET predicted a genetic advance of 1% per year and genetic
advance estimated at 1% genetic improvement for protein content in the cultivar trials.
No significant trend was observed in the elite trials of the Free State with TRET. Yield
showed 0.5% and 0.6% per year improvement for the two planting dates of the eastern
cultivar trials of Free State. A yield improvement of 0.3% per year improvement for the
two planting dates of the central cultivar trials of Free State was determined. A genetic
advance for yield of 0.7% per year was found in the warm region of the elite irrigation
trials and 9% yield improvement per year for the first planting date of the eastern region
of the cultivar irrigation trials. A negative trend was observed for the second planting date
of eastern region of both elite and cultivar irrigation trials.
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The effects of GEI on yield and quality traits were studied by comparing the AMMI and
GGE analyses. These methods portrayed similar results. An advantage of these
techniques is their complementary nature. Although both models portray GEI in various
biplots, the AMMI provides statistical evidence to the visual presentation of the GGE
biplots. Pearson product moment correlation matrix provided a linear relationship among
the variables studied. Principal component analysis (PCA), cluster analysis (CA) and
discriminant analysis (DA) offered auxiliary information on the relationship among the
factors (e.g. genotypes, years, localities and/or environments) and the variables. DA was
not able to indicate direction of genetic improvement in either of the three production
areas in this study.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ufs/oai:etd.uovs.ac.za:etd-10282014-142459 |
| Date | 28 October 2014 |
| Creators | Booyse, Marde |
| Contributors | Prof K.W. Pakendorf, Prof M.T. 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-10282014-142459/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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