Chemeli, Jane2016-09-262016-09-262016-02http://ir-library.ku.ac.ke/handle/123456789/15056A thesis submitted in partial fulfillment of the requirements for the award of the degree of Master of Science (Genetics) in the School of Pure and Applied Sciences of Kenyatta University. February 2016Maize is an important staple food for most Kenyans. The increasing population trend in the face of declining yields in maize production has intensified food insecurity countrywide. The low grain yield can be attributed to foliar diseases mainly gray leaf spot and maize streak virus and expensive hybrid seeds. Hybrid testing is expensive and limited in number of hybrids that can be generated and tested each year. This has increased the need to improve maize production techniques to meet the high demand. Assigning germplasm into different heterotic groups is fundamental for exploitation of heterosis for hybrid development within a shorter period thus reducing the cost. The objectives of this study were to identify good hybrids based on grain yield data and other yield related traits, to estimate the specific combining ability and percentage heterosis of hybrids formed and identify lines with good combining that can be used as parents in hybrid combination and classify the selected KALRO lines into heterotic groups. Eleven inbred lines were crossed with two single cross testers MU021 and MU022 developed by Kenya Agricultural and Livestock Research Organization (KALRO) Muguga South and belonged to heterotic groups A and B respectively. Line by tester design was used for making crosses. Twenty two crosses were evaluated in a randomized incomplete block design (RIBD) with two replications during the long rainy seasons between March and November 2012.The study was carried out in two different sites, at KALRO Muguga South and KALRO Embu. The parameters measured included plant height (cm), ear height (cm) and grain weight per plot in grams. Disease scores for gray leaf spot (GLS) and maize streak virus (MSV) were recorded and analyzed using Kruskal-Wallis Test. Data collected on plant height, ear height and yield were analyzed by Analysis of Variance (ANOVA) using Genstat programme 2012 and means separation was done using Tukey‘s 95% confidence intervals. Heterosis, general combining ability (GCA) and specific combining ability (SCA) were calculated using line by tester analysis. GCA mean squares due to lines and testers were highly significant p< 0.01 for plant height and ear height. GCA effects indicated that V217-48, Z426-43Z387-4-1 and Z419-5Z443-3 were the best general combiners for grain yield. V131-303 showed significant negative GCA effects. The good yielders in Embu were Z426-43Z387-4-1 X MU021, Z419-5Z443-3 X MU022,V217-48 X MU021, V217-48 X MU022 S458-2-2-2 X MU022 and V131-201 X MU021. In Muguga, the best performance were EC573(R12) Cross combinations S458-2-2-2 X MU021 or S458-2-2-2 X MU022 did well in the two counties. Inbred lines; V217-48 and V265-4-1 were resistant to both maize streak virus and Gray leaf spot in Muguga while inbred lines: Z419-5Z443-3, S458-2-2-2 and V131-201 showed resistance to both MSV and GLS. Total GCA mean squares were greater than SCA mean squares (GCA/SCA ratios of >1) indicating a preponderance of additive over non additive gene action. The basis of grouping the germplasm into different heterotic groups was specific combining ability (SCA) effects for grain yield. V131-303, Z426-43Z387-4-1, V217-48 and V131-201 showed negative SCA effects for grain yield with MU022 and were place into heterotic group B. EC573(R12)C853-14, V265-4-1, Z419-5Z443-3, V217-5, V265- 80, REGN99/48-2 and S458-2-2-2 showed negative SCA effects for grain yield with MU021 and were placed into heterotic group A. The general, specific combining abilities and heterotic groups showed that these genotypes had a potential hybrids for advanced yield testing and subsequent release in the specific locations.enThesis