Combining Ability of Highland Adapted Maize (Zea Mays. L) Inbred Lines For Desirable Agronomic Traits Under Optimum and Low Nitrogen Conditions

Low soil nitrogen is among the most important abiotic stresses limiting maize production in the highlands of Ethiopia. Information on hybrid performance and combining ability of maize inbred lines for grain yield and agronomic traits under low nitrogen stress is crucial to design appropriate breeding strategies for the development of enhanced maize cultivars. The objective of the present study was to estimate combining abilities of double haploid (DH) maize inbred lines for grain yield and related traits under optimum nitrogen and low nitrogen (N stress) condition. 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 optimum nitrogen and Low nitrogen environments. The genotypes were evaluated in alpha lattice design replicated twice in both environments. Analyses of variances showed significant mean squares due to crosses for most traits studied. At optimum nitrogen condition, the highest grain yield was obtained from crosses L4 x L8 (9.57 t ha-1), L4 x L7 (8.67 t ha-1), L1 x L3 (8.36 t ha-1), L6 x L8 (8.27 t ha-1) and L3 x L4 (8.00 t ha-1), whereas at low nitrogen condition, L2 × L4 (6.74 t ha-1) and L4 × L8 (5.15 t ha-1) were crosses with higher grain yield values. Mean squares due to general (GCA) and specific (SCA) combining abilities were significant for most of the traits under both conditions. This indicates that both additive and non-additive gene actions are important in the inheritance of these traits. 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. L3 and L8 were found as good combiners for grain yield at optimum N environment, whereas L2, L4 and L7 were good general combiners under low N stress condition. L4 and L8 were good combiners for grain yield in combine analysis across environments and hence were promising parents for hybrid cultivars development. Based on SCA effects, L1×L5, and L4×L7 were identified as promising hybrids for majority of traits studied in combined analysis across environments