Combining Ability Of Chilo Partellus Resistant Maize Inbred Lines For Mid-altitude Ecology Of Kenya
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Maize (Zea mays L.) is an important staple food crop in the developing world. The spotted stem borer, Chilo partellus Swinhoe is an important stem borer causing significant maize yield losses in the mid-altitude ecology of Kenya. Host plant resistance is a preferred option to reduce yield losses among the available methods used to manage stem borers. Breeders have developed inbred lines resistant to a number of stem borer species. The objectives of the study included allocating ten putative Chilo partellus resistant maize inbred lines into their heterotic groups, assess the biotic resistance present and measure the agronomic performance of F I hybrids made from these lines. The inbred lines were crossed in a diallel mating scheme to generate 45 single crosses, which, together with five commercial checks, were used to form a trial with 50 hybrids. These were evaluated at four sites for two rainfall seasons in 2009 and 2010. Ten plants in every plot were artificially infested using first instar neonates of C. partellus while the rest were protected using beta cyfluthrin (Bulldock). Data were recorded on grain yield, stem borer leaf damage, and number of exit holes, tunnel length, and ratio of tunnel length to plant height, anthesis and silking dates, plant and ear heights, ear and plant aspect. Analysis of variance was carried out on the data using GLM procedure of SAS. Results showed variability (P<0.001) among the ten lines for resistance to the spotted stem borer, grain yield potential and agronomic performance. Six parents were classified into heterotic group B while only one parent was classified into heterotic group A. Two parents were placed into heterotic group AB. Grain yields ranged between 8.02 - 3.37 t/ha under infestation. Additive gene effects were found to be more important than non-additive gene effects for grain yield and leaf damage, number of exit holes, tunnel length and tunnel lengthplant height ratio. However, genotypes x parameter interactions were observed between grain yield and leaf damage, number of exit holes and tunnel length. GCA estimates ranged between -1.2 and 1.1, with parents 1 and 2 showing significant (p=0.001) grain yield superiority, 3 and 4 had significant (p=0.001) good expressions for stem borer resistance in hybrids while parent 9 showed good performance for both grain yields and resistance. Thus, inbreds 1, 2 and 9 were identified as being potentially good breeding stocks. Results also showed parent 1 to flower significantly (p=0.05) earlier than the rest. There was no variability in reaction to gray leaf spot, Exserohilum turcicum, and rust and maize streak virus among the hybrids across the various environments. It was concluded from this study that additive gene action was very important in controlling stem borer resistance in the materials used. Future inbred lines with useful resistance to stem borers were identified and single crosses useful in the development of high-yielding stem borer-resistant hybrids formulated. It was further concluded that it would be possible to develop viable F 1 hybrids resistant to C. partellus and with desirable agronomic traits through recurrent selection. It was recommended that reaction of ten identified inbred lines resistant to C. partellus and Busseolafusca (Fuller) should be confirmed through exposing them to higher intensities of attack than those used in the study.