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dc.contributor.advisorLabuschagne, M. T.
dc.contributor.authorMawere, Sabastian Shangwa
dc.date.accessioned2015-11-12T13:13:15Z
dc.date.available2015-11-12T13:13:15Z
dc.date.copyright2007-11-27
dc.date.issued2007-11-27
dc.date.submitted2007-11-27
dc.identifier.urihttp://hdl.handle.net/11660/1633
dc.description.abstractEnglish: Since the initiation of a product oriented breeding programme aimed at improving maize for drought prone mid altitudes of southern Africa, CIMMYT developed several inbred lines and single cross hybrids using pedigree selection methods, with emphasis on earliness, drought and low nitrogen stress tolerance. This resulted in increased volumes of seed inventories. Sixteen inbred lines and 71 single cross hybrids were crossed to three (single cross) testers, CML312/CML442 and CML505/CML509 (heterotic group A) and CML395/CML444 (heterotic group B) and evaluated as two separate experiments for general and specific combining ability in contrasting environments (optimal, managed drought and nitrogen stressed). The objective was to asses the relative importance of general combining ability (GCA) and specific combining ability (SCA) in identifying promising early maturing maize lines, single crosses and testers that could tolerate drought and nitrogen stress conditions, thus simulating prevailing conditions in most resource poor farmers’ fields in the mid altitude environments of southern Africa. The first experiment consisted of 48 experimental crosses and 24 additional crosses. Six trails were planted in a lattice (Alpha 0,1) with eight plots per incomplete block. The second experiment consisted of 213 experimental crosses and additional 27 double crosses and synthetics. Five trials were planted in a lattice (Alpha 0,1) with 12 plots per incomplete block. Trials were planted under optimal conditions at ART farm, Rattray Arnold and Kadoma, nitrogen stressed conditions at Harare and drought stressed conditions at Chiredzi in Zimbabwe in 2006. Data was collected on grain yield (GY), anthesis dates (AD), anthesis silking interval (ASI), plant heights (PH), ears per plant (EPP), and leaf senescence (SEN). Data was analysed first according to Lattice (alpha 0.01) design using computer software Fieldbook, for the general performances of all crosses for all traits. Line x tester analysis for general combining ability and specific combining ability was performed using SAS and AGROBASE II computer software. The first experiment identified heterotic group B line 15 as superior with a GCA value of 0.56. The line had a SCA value of 0.21 with early maturing (heterotic group A tester) CML505/CML509. The hybrid had grain yield of 7.9t/ha and 1.3t/ha across optimal and stress environments respectively and was early maturing (69 days) (silking anthesis days). In the second set of materials heterotic group A single crosses 51, 37, 55, and 7 had good general combining ability above 0.64. Heterotic group B single crosses 11, 38, 39 and 22 had good specific combing ability with CML505/CML509. The hybrid combinations ranged between 6.1-7.4 t/ha across optimal environments and 0.8-1.4 t/ha across stressed environments. These hybrids were very early (AD 64-66 days), could be evaluated in wide environments for GCA with heterotic group A lines and single crosses in order to identify an early maturing group B tester. CML505/CML509 classified the early maturing lines and single crosses into heterotic groups better than CML312/CML442.en_ZA
dc.description.abstractAfrikaans: Sedert die begin van produk georiënteerde teelprogramme wat gemik is op die verbetering van mielies vir die droogte geneigde mid-hoogte areas van suidelike Afrika, het CIMMYT verskeie ingeteelde lyne en basters ontwikkel met stamboomteling, met klem op vroegheid, droogte en lae stikstof toleransie. Dit het gelei tot meer saadbronne. Sestien ingeteelde lyne en 71 enkelkruis basters is gekruis met drie (enkelkruis) toetsers, CML312/CML442 en CML505/CML509 (heterotiese groep A) en CML395/CML444 (heterotiese groep B) en is geëvalueer in twee verskillende eksperimente vir algemene en spesifieke kombineervermoë in kontrasterende omgewings (optimaal, en beheerde droogte en stikstof gestremde toestaande). Die doel was om die relatiewe belangrikheid van algemene (GCA) en spesifieke (SCA) kombineervermoë te bepaal om sodoende goeie potensiële vroeë lyne, enkelkruise en toetsers te identifiseer wat tolerant is vir droogte en lae stikstof toestande, deur dus die toestande in meeste hulpbron arm boere se lande te simuleer in die mid-hoogte omgewings van Suidelike Afrika. Die eerste eksperiment het bestaan uit 48 eksperimentele kruisings en 24 addisionele kruisings. Vyf proewe is geplant in ‘n alfa tralie met 12 persele per onvolledige blok. Die proewe is geplant onder optimale toestande by ART plaas, Rattray Arnold en Kadoma, stikstof gestremde proewe by Harare en droogte gestremde toestande by Chiredzi in Zimbabwe in 2006. Data is ingesamel op graanopbrengs (GY), antese datum (AD), antese baard interval (ASI), plant hoogte (PH), koppe per plant (EPP), en blaar verdroging (SEN). Data is geanaliseer met die alfa tralie ontwerp met die Fieldbook sagteware; vir algemene evaluering van alle kruisings vir alle eienskappe. Lyn x toetser analise vir algemene en spesifieke kombineervermoë is gedoen met SAS en AGROBASE II sagteware. Die eerste eksperiment het heterotiese groep B lyn 15 as die beste uitgewys met ‘n GCA waarde van 0.56. Die lyn het ‘n SCA waarde van 0.21 gehad met vroeë ryp (heterotiese groep A toetser) CML505/CML509. Die baster het ‘n graanopbrengs van 7.9t/ha en 1.3t/ha onder optimale en stremmingstoestande afsondelik gehad, en was vroeg ryp (69 dae tot baard antese). In die tweede stel material het heterotiese groep A enkelkruise 51, 37, 55, en 7 goeie algemene kombineervermoë gehad bo 0.64. Heterotiese groep B enkelkruise 11, 38, 39 en 22 het goeie spesifieke kombineervermoë gehad met CML505/CML509. Die baster kombinasies het gewissel tussen 6.1-7.4t/ha oor optimale omgewings, en 0.8-1.4t/ha oor gestremde omgewings. Hierdie basters was baie vroeg (AD 64-66 dae), en kan oor verskillende omgewings geëvalueer word vir GCA met heterotiese groep A lyne en enkelkuisings om ‘n vroeg-ryp groep B toetser te identifiseer. CML505/CML509 het die vroeg-ryp lyne en enkelkruise in beter in heterotiese groepe verdeel as CML312/CML442.af
dc.language.isoenen_ZA
dc.publisherUniversity of the Free Stateen_ZA
dc.subjectDissertation (M.Sc.Agric. (Plant Sciences: Plant Breeding))--University of the Free State, 2007en_ZA
dc.subjectCorn -- Drought toleranceen_ZA
dc.subjectHybrid cornen_ZA
dc.subjectCorn -- Breedingen_ZA
dc.subjectCrops and nitrogenen_ZA
dc.titleHeterotic patterns and combining ability of CIMMYT early maize (Zea mays L.) lines under moisture and nitrogen stress and optimal conditionsen_ZA
dc.typeDissertationen_ZA
dc.rights.holderUniversity of the Free Stateen_ZA


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