Inheritance of stem borer resistance in maize (Zea Mays L.)

English: 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.