Browsing by Author "Okori, P."

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    Mechanisms and Sources of Resistance in Tropical Maize Inbred Lines to Chilo partellus Stem Borers
    (2013) Munyiri, S. W. 1,2; Mugo, S. N. 3; Otim, M. 4; Mwololo, J. K. 1,5; Okori, P.
    Developing maize with durable resistance to maize stem borers could be enhanced by identifying genotypes with different mechanisms of resistance and pyramiding the resistances into high yielding genotypes. This study was carried out on 120 CIMMYT tropical maize inbred lines to identify the most important mechanisms of resistance that could be used to discriminate the germplasm into resistant or susceptible categories. The experiment was laid in an α-lattice design, and replicated three times during the 2011/12 seasons. Traits measured were leaf toughness, stem penetrometer resistance, trichome density, stem sugar content, leaf damage, number of stem exit holes and stem cumulative tunnel length. A selection index was computed and categorized the 120 inbred lines into 33 resistant, 29 moderately resistant, 31 moderately susceptible and 27 susceptible. The most resistant lines were those derived from the CIMMYT multiple borer-resistant populations with CKSBL10039 being most resistant and CML395 most susceptible with indices of 0.49 and 1.84, respectively. Trichome density, leaf toughness and stem sugar content in that order were the most important traits in discriminating the lines into resistance and susceptible categories. More research is needed to classify the specific types of trichomes and sugars present in both resistant and susceptible inbred lines.
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    Quantitative Trait Loci Mapping in Maize for Resistance to Larger Grain Borer
    (2018) Mwololo, J. K.; Okori, P.; Munyiri, S. W.; Otim, M.; Mugo, S. N.
    Storability of maize grain is constrained by the larger grain borer (LGB) (Prostephanus truncatus). Host plant resi- stance is the most feasible way to manage LGB among smallholder farmers. Breeding for resistance to this pest in maize is dependent on understanding genetic mechanisms underlying the resistance. The objective of this study was to map quantitative trait loci (QTL) associated with LGB resistance in tropical maize. A mapping population of 203 F2:3 derived progenies was developed from a cross between susceptible and resistant inbred lines. The F2:3 progenies were crossed to a tester and testcrosses evaluated across six environments followed by screening for resistance to LGB. Data was collected on husk cover tip length, and grain texture in the field. Biochemical traits were analyzed on the maize grain. Harvested grain was evaluated for resistance and data recorded on grain damage, weight loss and number of insects. Grain hardness was measured as a putative trait of resistance. Uni- variate analysis of variance for all the traits was done using the general linear model of statistical analysis system. Genetic mapping was done using Joinmap 4, while QTL analysis was done using PLABQTL. The QTL for resistance were mapped to 6 out of the 10 chromosomes. QTL for resistance traits were located in chromosomes 1, 5 and 9. Chromosome 1 had a common QTL linked to protein content, grain hardness and husk cover tip length. Additive genetic effects were prevalent in all detected QTL. Overall, the studies show that breeding for resistance to LGB is possible.