Labuschagne, M. T.Van Rensburg, J. B. J.Andre, Adriano Muiocoto2017-05-232017-05-232001-05http://hdl.handle.net/11660/6283English: The stem borer Busseala fusca (Lepidoptera: Noctuidae) is an important pest in maize production in South Africa and many other countries South of the Sahara. The mean goal of the present study was to gather information about the genetic and phenotypic characteristics of B. fusca resistance in maize as a help to understand the nature of the resistance in order to overcome the difficulties standing in the way of transfer of the resistance from available sources to the local and adapted cultivars. The inheritance was studied through assessment of the resistance on basis of phenotypic expression after artificial infestation with first instar larvae of B. fusca of 36 crosses of 18 susceptible inbred lines with two sources of resistance, CML 139 and Mp706. Plants were evaluated for characters like leaf feeding, larval mass gain, internal damage and yield losses. A scaling test was used to analyse the data. Results indicated that additive, dominant and non-heritable parameters were all important for B. fusca resistance. GCA and SCA values indicated good performance of the crosses for additive and dominant gene effects (heterosis). The correlation coefficient was used to evaluate the relatedness of three parameters of assessment of the resistance and the result indicated that there are significant correlations between leaf feeding, larval mass gain and internal damages caused by the insect. Different levels of inheritance from the two sources were seen in each cross indicating that the resistance is inherited differently, depending on the source used. F2:3 lines were obtained from selected crosses (CML 139 xP608) and (Mp706 xP608) for AFLP analysis. The analysis of the 10 categories of phenotypic assessment evaluated for the fragment segregation indicated that additive gene contribution from the parents was present at several loci. This was in agreement with negligible one locus non allelic interaction found by the scaling test for absence of epistasis. Different fragments were found to be specific for resistant parents and the progeny, which indicated that dominance was again present in the inheritance of the resistance. In this study we have concluded that despite attempts to improve the varieties' resistance by transfer of the resistance from resistant sources to more adapted varieties, the polygenic nature of the resistance and the presence of high levels of non-inherited parameters are still the most important cause of ineffective use of conventional methods of breeding. The use of markers to tag the genetic information about the inheritance of the resistance in cross progenies of resistant and susceptible varieties is seen as one of the ways to overcome this barrier. Unfortunately the use of this important tool is still not perfected for use in this particular area of science. Until the perfection of molecular marker technology, the recurrent selection approach will have to be used for insect resistance improvement in maize cultivars.Afrikaans: Die stamboorder Busseola fusca (Lepidoptera: Noctuidae) is "n belangrike insekplaag in mielie produksie in Suid Afrika en heelwat ander lande suid van die Sahara. Die doel van hierdie studie was om inligting in te samel van genetiese en fenotipiese eienskappe van Busseola fusca weerstand in mielies as 'n metode om die aard van die weerstand te verstaan, om oordrag van weerstand van weerstandsbronne na plaaslike en aangepaste cultivars te vergemaklik. Die oorerflikheid is bestudeer deur evaluasie van weerstand op die basis van fenotipiese uitdrukking na kunsmatige infestasie met eerste instar larwes van Busseola fusca in 36 kruisings van 18 vatbare ingeteelde lyne met twee weerstands bronne CML 139 en Mp706. Plante is geëvalueer vir eienskappe soos blaar voeding, larwes se massa toename, interne skade en opbrengs verliese. Resultate het aangetoon dat additiewe, dominant en nie-oorerflike parameters almal belangrik was vir Busseola fusca weerstand. GCA en SCA waardes het goeie additiewe en dominante geen aksie (heterose potensiaal) van kruisings aangetoon. Korrelasies is gebruik om verwantskappe tussen drie parameters van weerstands evaluasie te bepaal. Die resultate het aangetoon dat daar betekenisvolle korrelasies is tussen blaar voeding, larwes se massa toename en interne skade veroorsaak deur die insek. Verskillende vlakke van oorerwing van die twee weerstandsbronne was duidelik in elke kruising, wat aantoon dat weerstand verskillend oorgeërf word afhangend van die weerstandsbron wat gebruik is. F2:3 lyne is gekry vanaf geselekteerde kruisings (CML 139xP608 en Mp706xP608) vir AFLP analise. Die analise van die 10 kategorië van fenotipiese evaluasie wat gebruik is vir fragment skeiding het aangedui dat die additiewe bydrae van die ouers teenwoordig was by verskillende loci, wat in ooreenstemming was met die weglaatbare een lokus nie-alleliese interaksie wat gevind is in die skaal toets vir afwesigheid van epistase. Verskillende fragmente is gevind wat spesifiek was vir weerstandbiedende ouers en nageslag, wat aangedui het dat dominansie weereens teenwoordig was by oorerwing van weerstand. In hierdie studie is die gevolgtrekkings gemaak dat ten spyte van die poging om cultivars se weerstand met oordrag van weerstandbronne na aangepaste cultivars te verbeter, die poligeniese aard van weerstand en die hoë vlakke van nie oorerflike parameters die grootste oorsaak is van oneffektiewe gebruik van konvensionele teeltegnieke. Die gebruik van merkers om genetiese inligting te merk van oorerwing van weerstand in die kruisings nageslag van weerstandbiedende en vatbare ouers is een manier om hierdie probleem te oorkom. Ongelukkig is die gebruik van hierdie tegnologie nog nie perfek vir hierdie gebied in die wetenskap nie. Totdat die tegnologie vervolmaak is, sal die herhalende seleksie benadering nog gebruik moet word vir verbetering van insek weerstand in mielies.enStem borersCorn -- Disease and pest resistanceThesis (Ph.D. (Plant Breeding))--University of the Free State, 2001ThesisUniversity of the Free State