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dc.contributor.advisorLabuschagne, M. T.
dc.contributor.advisorHerselman, L.
dc.contributor.advisorMagorokosho, C.
dc.contributor.authorNdhlela, Thokozile
dc.date.accessioned2015-09-08T10:08:58Z
dc.date.available2015-09-08T10:08:58Z
dc.date.copyright2012-06
dc.date.issued2012-06
dc.date.submitted2012-06
dc.identifier.urihttp://hdl.handle.net/11660/1200
dc.description.abstractEnglish: 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 Rogers’ 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.en_ZA
dc.description.abstractAfrikaans: Die ontwikkeling van genotipes vir Zimbabwe wat droogte en lae N tolerant is kan ‘n belangrike bydrae maak om die probleem van voedselsekuriteit aan te spreek. Beide CIMMYT en DR&SS mieliekiemplasma is in hierdie studie gebruik wat uitgevoer is in Zimbabwe in die 2009/10 en 2010/11 seisoene. Die proewe is uitgevoer onder optimum, droogte en lae N toestande. Een van die belangrikste doelwitte was om kombineervermoë en heterose vir graanopbrengs en ander agronomiese eienskappe van wit mielie ingeteelde lyne onder stremmings en optimale toestande te bepaal. Lyn x toetser analise van 23 ingeteelde lyne het RS61P, NAW5885 (van DR&SS) en CML444, CML539, CML442, CML537 en CML548 (van CIMMYT) geïdentifiseer as lyne met die beste GCA effekte onder beide droogte en lae N toestande. Beide additiewe en nie-additiewe geeneffekte was belangrik by die uitdrukking van eienskappe oor alle omgewings; maar nie-additiewe geeneffekte was meer belangrik by die uitdrukking van eienskappe onder stremmingstoestande. Die enkelkruise RS61P/CML444 en 2N3d/CML548 is geïdentifiseer as potensiële toetsers vir die SC en N3 heterotiese groepe onderskeidelik. In die analise van G x E en stabiliteit met die gebruik van AMMI en GGE biplotte is dieselfde enkelkruise as die mees stabiel geïdentifiseer. Daar was drie mega-omgewings binne die toetsomgewings en die “Agricultural Research Trust” plaas omgewing was die mees effektief om te onderskei tusssen genotipes. Genetiese diversiteit tussen die 23 ingeteelde lyne is ondersoek met die gebruik van 14 morfologiese eienskappe en 1 129 SNP merkers. Die morfologiese data data het variasie tussen ingeteelde lyne gewys wat gemanipuleer kan word deur seleksie en hibridisasie. Variasie is verder bevestig met die gebruik van PCA waar totale variasie nie verklaar kon word deur enkele eigenvektore nie, en waar die meeste variasie verklaar is deur graanopbrengs, tekstuur, kopaspek, gewone roes, GLS en dae tot antese. Euklidiese en Rogers se matrikse van verskille gebasseer op morfologiese en SNP data onderskeidelik het in sommige gevalle die lyne gegroepeer volgens stambome. Die SNP dendrogram het die hoogste akkuraatheid (r=0.87) getoon in vergelyking met die morfologiese dendrogram, wat gewys het dat lyne effektief gegroepeer is, alhoewel dit soms nie in ooreenstemming was met bekende heterotiese groeperings wat vroeër bepaal is met toetsers nie. Die evaluasie van korrelasies tussen genetiese afstande, F1 prestasie, heterose en SCA het betekenisvolle positiewe korrelasie en regressie tussen SCA, MPH, 267 HPH en per se prestasie van basters getoon. Die HPH en MPH was ook betekenisvol positief geassosieër en liniêre regressie sowel as ‘n hoë koeffisiënt van bepaling is gesien met die per se prestasie van basters, veral onder droogtetoestande. Korrelasies van genetiese afstande met MPH en HPH was te laag om voorspellingswaarde te hê. ‘n Gemiddeld van 112.29% MPH en 76.40% HPH is gesien oor omgewings. Dit is ‘n aanduiding van die potensiaal van hierdie ingeteelde lyne vir basterontwikkeling. Die segregerende F3 lyne is getoetskruis met groep A (CML539/CML442) en B (CML444/CML395) toetsers en toetskruise van lyne afkomstig van DR&SS lines K64r, RS61P, NAW5885, SC5522 en CIMMYT droogtetolerante skenkers gebasseer op DTPWC9 was oor die algemeen die beste presterende toetskruise in die vroeë en laat rypheidstyd proewe. Drierigting basterprestasie is voorspel vanaf 11 enkelkruise en resultate het getoon dat daar betekenisvolle maar lae korrelasies was tussen die voorspelde en die werklike graanopbrengs. Dit kon verklaar word deur die epistatiese en betekenisvolle G x E interaksies wat nie in ag geneem is in die voorspellingsformule nie. Drierigtingkruisbasters wat geïdentifiseer is wat baie goed presteer het onder beide droogte en optimum toestande, was RA214P/CML538//RS61P, RS61P/CML444//CML538 and RS 61P/CML444//CML539. Dit is egter nog steeds nodig om hierdie basters onder lae N toestande te evalueer voor hulle aanbeveel kan word vir vrystelling.af
dc.description.sponsorshipCIMMYTen_ZA
dc.language.isoenen_ZA
dc.publisherUniversity of the Free Stateen_ZA
dc.subjectCombining abilityen_ZA
dc.subjectGenetic diversityen_ZA
dc.subjectHeterosisen_ZA
dc.subjectMaize -- Zimbabween_ZA
dc.subjectMaize -- Disease and pest resistance -- Zimbabween_ZA
dc.subjectThesis (Ph.D. (Plant Sciences: Plant Breeding))--University of the Free State, 2012en_ZA
dc.titleImprovement strategies for yield potential, disease resistance and drought tolerance of Zimbabwean maize inbred linesen_ZA
dc.typeThesisen_ZA
dc.rights.holderUniversity of the Free Stateen_ZA


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