Abstract:
Quality protein maize (QPM) is a type of maize whose nutritional value has been enhanced through conventional breeding. The production of hybrid QPM is started very recently in Ethiopia that requires extensive research to exploit heterosis to increase the productivity of the crop. Exploitation of heterosis through the production of hybrids is proven breeding method to improve the yield of maize. Accordingly, the objectives of this study were to estimate the magnitude of heterosis and combining abilities in crosses of 10 mid altitude adapted QPM inbred lines and to determine the association among morph-agronomic traits. The crossing and experiment was conducted at Bako National Maize Research Center during the 2014 and 2015 main cropping season, respectively. Forty five F1 hybrids obtained by crossing 10 inbred lines in diallel fashion (without parent and reciprocals) along with their parental lines and four standard checks were planted in two separate trials on adjacent experimental blocks. The experimental design used was alpha lattice for the hybrid trial and randomized complete block design for inbred lines trial with three replications. Each entry was planted on a one-row plot of 5.1 m length with 0.75 m and 0.3 m spacing between rows and plants, respectively for each trials. Data on phenology, growth, grain yield and yield related traits, and disease reaction were collected at the appropriate plant growth stages. The mean squares due to hybrids and parents were highly significant for all traits except common leaf rust in the hybrids trial and diseases parameters, stem lodging, bad husk cover and ear rot indicating the existence of genetic variability for most traits. Highest positive mid and better parents heterosis was observed for grain yield and yield related traits indicating the possibility of increasing grain yield and yield related characters via hybridization. Negative heterosis was observed for phenology and growth traits, and diseases parameters as well. The mean squares due to general and specific combining ability were significant for all the traits except days to silking, harvest index and total above ground biomass which shows the importance of additive and non-additive gene action in the inheritance of the character. In most, about 60% of the traits, including yield, however, relative importance of general to specific combining ability was lower than unity denoting the predominance of nonadditive gene. This study enable to identify parental lines that can combine for more than one trait: L2 and L6 showed the tendency were earliness and had shorter plant stature. L1 and L10 appeared to be ideal parents for increasing grain yield and yield related traits. L9 and L8 showed better resistance to foliar diseases. Based on the specific combining ability effect of the hybrids, the current study also identified L4 x L1 (11.5 t ha-1) best cross combination which could be proposed for possible release after one more evaluation or as breeding source material. Grain yield had highly significant positive association with plant height, ear plant-1, ear length and number of kernel row-1and negative correlation with anthesis silk interval, plant and ear aspect, total above ground biomass, common lea rust, phaeosphaeria leaf spot and ear rot at both genotypic and phenotypic level. In addition, plant height, ear plant-1, ear length an number of kernel row- had positive direct effects and anthesis silk interval, plant aspect, phaeosphaeria leaf spot and ear rot had negative direct effects on grain yield at both genotypic and phenotypic level; while, total above ground biomass and common leaf rust had negative direct effects at genotypic and days to anthesis, ear height, root lodging and ear aspect had negative direct effects on grain yield at phenotypic level. This indicated that, by increasing the positive and decreasing the negative direct effects of the traits grain yield could increase invariably.