Combining ability of highland adapted maize (Zea mays L.) inbred lines for grain yield and yield related traits under optimum and low nitrogen conditions

Maize is staple cereal crop in Ethiopia despite the fact that its production is constrained by nitrogen deficiency due to the high cost of fertilizer, and risks of drought. Therefore, development of maize varieties for low nitrogen might be one of the options to overcome the problem. The objective of this study was to estimate combining ability of highland maize inbred lines for yield and yield related traits under low nitrogen (low N) stress and non-stress conditions. Twenty-six inbred lines (two heterotic testers and twenty-four lines) were crossed using line × tester mating design, which  generated 48 F1 hybrids and along with two hybrid checks (AMH853 and AMH 851) that were evaluated using alpha lattice design with two replications for grain yield and yield related traits within 2017 cropping season at Ambo under low and optimum nitrogen. Analyses of variances showed significant mean squares due to crosses for all traits under both low N stress and non-stress conditions, except for ear per plant under low N stress condition. The mean squares for general (GCA) and specific (SCA) combining abilities were significant for most of the traits under both conditions. Generally, the study indicated the importance of both additive and non-additive gene effects in most cases, while non-additive gene effects are less important under low-N stress. Inbred lines L1, L2, L9 and L20 were found as good combiners for grain yield at optimum N environment, whereas L5 and L14 were good general combiners under low N stress condition. L20 were good combiner for grain yield in combine analysis across environments and hence were promising parents for hybrid cultivars development. Based on SCA effects and per se performance, L5×T2 and L7×T2 were identified as promising hybrids for majority of traits studied in combined analysis across environments.   Key words: General combining ability, gene action, heterotic group, specific combining ability.