Heterosis and combining ability of highland adapted maize (Zea mays. L) DH lines for desirable agronomic traits

Maize (Zea mays L.) is one of the cereals that provide calorie requirements in the majority of Ethiopians diet. The national average maize yield in Ethiopia is low and thus knowledge of combining ability and heterosis is a prerequisite to develop high yielding maize varieties. The objective of the present study is to estimate combining abilities of double haploid (DH) maize inbred lines for grain yield and related agronomic traits, and to identify crosses with higher standard heterosis. A total of 36 diallel crosses generated by crossing nine maize DH lines using half diallel mating scheme and four standard checks were studied for different desirable agronomic traits during 2017 cropping season at Ambo and Kulumsa Agricultural Research Centers. The genotypes were evaluated in alpha lattice design replicated twice in both locations. Analyses of variances showed significant mean squares due to crosses for most traits studied. The highest grain yields were obtained from crosses L1 x L3, L3 x L8, L4 x L8 and L8 x L9. GCA mean squares were significant for all studied traits, while SCA mean squares were significant only for grain yield, days to anthesis, ear per plant and ear diameter. Relatively larger GCA over SCA variances were observed in the current study for most studied traits revealing the predominance of additive gene action in controlling these traits. Of the DH inbred lines, L3 and L8 were the best general combiners for grain yield, and hence are promising parents for hybrid development. Inbred lines  L2, L4, L6, L7 and L8 were good combiners for earliness whereas, L1, L2 and L6 showed negative and significant GCA effects for plant and ear height. In this study, none of the crosses showed positive and significant standard heterosis for grain yield.   Key words: Combining ability, general combining ability, highland maize, standard heterosis, specific combining ability.