Breeding for drought and low N tolerant genotypes in Zimbabwe is an important
intervention that will see the country curbing the food in-security problem. Both CIMMYT
and DR&SS maize germplasm was used in this study that was conducted in Zimbabwe in
the 2009/10 and 2010/11 seasons. Evaluations were done under optimum, drought and low
N conditions. One of the objectives was to estimate combining ability and heterosis for
grain yield and other agronomic traits of white maize inbred lines under stress and optimal
environments. Line x tester analysis of 23 inbred lines identified RS61P, NAW5885 (from
DR&SS) and CML444, CML539, CML442, CML537 and CML548 (from CIMMYT) as
having desirable GCA effects under both drought and low N conditions. Additive and nonadditive
gene effects were important in the expression of traits across all environments;
however non-additive gene effect assumed a more important role in the expression of traits
under stress environments. The single crosses RS61P/CML444 and 2N3d/CML548 were
identified as potential testers for the SC and N3 heterotic groups respectively. In the
analyses of G x E and stability using AMMI and GGE biplot the same single crosses were
identified as the most stable. There were three mega environments identified within the test
environments and Agricultural Research Trust farm site was the most powerful in
discriminating genotypes. Genetic diversity amongst the 23 inbred lines was examined
using 14 morphological traits and 1 129 SNP markers. The morphological data revealed
variability amongst inbred lines that could be manipulated through selection and
hybridisation. Variability was further substantiated using PCA where the overall diversity
could not be explained by a few eigenvectors and the major contributors were grain yield,
texture, ear aspect, common rust, GLS and anthesis days. Euclidean and Rogersâ
dissimilarity matrices based on morphological and SNP data respectively clustered lines
related by pedigree together in some cases. The SNP dendrogram had a high goodness of fit
value (r=0.87) compared to the morphological dendrogram, which showed that it grouped
the lines efficiently, although at times it was not in agreement with the known heterotic
grouping that was previously established using testers. The assessment of correlation
between genetic distances, F1 performance, heterosis and SCA revealed significant positive
correlations and regressions between SCA, MPH, HPH and per se performance of hybrids. The HPH and MPH also showed significant positive association and linear regression along
with high coefficient of determination with per se performance of hybrids, especially under
drought conditions. Correlations of genetic distances with MPH and HPH were too low to
be of predictive value. An average of 112.29% MPH and 76.40% HPH were realised across
environments and this was an indication of the potential of these inbred lines for hybrid
development. The segregating lines at F3 stage were testcrossed to group A
(CML539/CML442) and B (CML444/CML395) testers and testcrosses containing lines
derived from DR&SS lines K64r, RS61P, NAW5885, SC5522 and CIMMYT drought
tolerant donors based on DTPWC9 were generally amongst the best performing testcrosses
in early and late maturing trials. Three-way hybrid performance was predicted from 11
single cross hybrids and results showed that there was significant but weak correlation
between the predicted and the observed grain yield means and this could be explained by
epistatic and significant G x E interaction, which were not taken into account in the
prediction equation. Three-way cross hybrids identified as having superior performance
under drought and well-watered conditions included RA214P/CML538//RS61P, RS61P/
CML444//CML538 and RS61P/CML444//CML539. However, there is still need to evaluate
these hybrids under low N conditions before they can be recommended for release.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ufs/oai:etd.uovs.ac.za:etd-05172013-120122 |
| Date | 17 May 2013 |
| Creators | Ndhlela, Thokozile |
| Contributors | Dr C Magorokosho, Prof L Herselman, 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-05172013-120122/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. |
Page generated in 0.0022 seconds