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Development of inbred lines is a routine activity in hybrid maize breeding program. Understanding the relative importance of general (GCA) and specific (SCA) combining ability effects for different traits of newly developed maize lines is of paramount importance to design future breeding strategies for the development of hybrid. There are several types of mating designs available to study the combining abilities of maize inbred lines, of which line x tester mating scheme is one used to determine the combining abilities and also to categorize the lines into heterotic groups. The objectives of the study were, therefore, to estimate GCA and SCA of newly developed highland maize lines using line x tester mating design, to identify best promising hybrid crosses with desirable traits for further breeding and cultivar development, and to identify the heterotic groups of the lines involved in the crosses. Twelve lines and four testers were involved in the study. A total of 48 testcrosses along with two checks were made available for evaluation across locations. An alpha lattice design (10x5) with two replications at each location was used. Two lines (L6 and L5) showed highly significant and positive GCA effects for grain yield. Besides, L6 also revealed positive GCA effects for the other yield related traits such as number of ears per plant (NEPP), number of rows per ear (NRPE), number of kernels per row (NKPR) and ear diameter (ED). On the other hand, crosses L7XT2, L8xT4, and L9xT1 had positive and significant SCA effects for grain yield. The lines and crosses with positive and significant GCA and SCA effects, respectively; could be selected for use in highland maize hybrid or/and synthetic cultivar development. The testers clearly categorized L3 and L6 into their respective heterotic groups in a similar pattern unlike the other lines which requires the application of molecular markers for further verification. [ABSTRACT FROM AUTHOR]

Maize ( Zea mays L.) yields are significantly lower in the tropical-highlands than other environments predominantly due to the lack of well-adapted and improved cultivars and due to genotype by environment (G × E) interaction. The objectives of this study were to determine G × E interaction and yield stability of quality protein maize (QPM) single-cross hybrids recently developed from tropical-highland adapted inbred lines, and to identify promising genotypes and representative test and seed production environments. The study was conducted at seven environments representing the tropical-highland sub-humid maize growing agro-ecology in Ethiopia. Sixty-six QPM hybrids and two commercial check hybrids were evaluated using a 4 × 17 alpha lattice design. Data were analysed using the additive main effects and multiplicative interaction (AMMI) and genotype and genotype by environment (GGE) biplot methods. Using AMMI analysis, four promising QPM hybrids were identified compared to the commercial checks and designated as hybrid 10 (KIT32 × 142-1-eQ), hybrid 66 (142-1-eQ × CML144), hybrid 59 (FS60 × 142-1-eQ), and hybrid 38 (FS67 × CML144) with grain yields of 10.3, 9.6, 9.4 and 8.9 t ha, respectively. The same hybrids were identified as the best performers for being close to the ideal cultivar using the GGE biplot analysis. The GGE analysis delineated the test environments into two mega-environments useful for targeted evaluation of genotypes and effective maize breeding and seed production. Kulumsa site during 2013 (KUL13) was the most suitable environment in discriminating the QPM hybrids and being a representative test environment. [ABSTRACT FROM AUTHOR]