Abstract:
Breeding efforts to convert elite mid-altitude normal maize inbred lines to quality protein maize (QPM) has a recent history in Ethiopia. For a successful QPM hybrid and synthetic variety development, generation of information on heterosis, and combining abilities of newly developed QPM inbred lines is necessary. Accordingly, this study was conducted to estimate the combining ability of QPM inbred lines for grain yield and yield related traits, to estimate the magnitudes of heterosis for grain yield and yield related traits in line x tester QPM hybrids and to classify inbred lines into heterotic groups. The crossings and field experiment was conducted at Bako National Maize Research Center during the 2015 and 2016 main cropping season, respectively. Fifty test crosses obtained by crossing 25 inbred lines with two testers using line x tester mating design along with their parents and two standard checks were evaluated in two separate trials using alpha lattice design with three replications. Analysis of variance showed that mean squares due to genotypes and per se performances of parents were highly significant for most of the traits studied. Combining ability analysis exhibited highly significant general combining ability (GCA) and specific combining ability (SCA) for grain yield (GY), days to anthesis, days to silking, days to maturity, anthesis-silking interval, ear height, plant height and reaction to gray leaf spot, indicating the importance of both additive and non-additive gene actions in the inheritance of the characters. However, the contribution of GCA variance was much greater than that of SCA variance for all the characters, suggested the predominance importance of additive gene action in the inheritance of traits. Inbred lines, L1, L3, L9, L13 and L15 were the best general combiners for grain yield. L16, L17, L18, L19 and L20 were good general combiners for earliness. Cross combinations L7 x T2, L11 x T1, L19 x T2, L20 x T2 and L22 x T2 displayed positive and significant SCA effects for GY. The study also separated inbred lines into different heterotic groups based on SCA effects and heterosis. As a result, ten inbred lines were assigned to heterotic group A; whereas, fifteen inbred lines were assigned to heterotic group B. The highest mid- and better- parent heterosis for grain yield were obtained from L15 x T1 (169.4%) and L3 x T1 (85.67%) respectively. Similarly, the highest standard heterosis was scored by L3 x T1 (20.21%). L6 x T1, L8 x T1 and L21 x T1 were scored negative and significant mid- and better-parent heterosis for disease parameters. The results obtained in this study suggested to use the indentified inbred lines for further breeding of QPM for the mid-altitude sub-humid agro-ecology of Ethiopia.