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Development of improved quality protein maize (QPM) varieties/hybrids would complement strategies for reducing problems of malnutrition in developing countries such as Ethiopia.The highland maize breeding program in Ethiopia, in collaboration with CIMMYT, has developed QPM inbred lines adapted to highland sub-humid maize agroecology. However, there is limited information on the genetic variability and interrelationship among the QPM inbred lines. The present study was, therefore, conducted to assess the genetic variability and thereby classify elite QPM inbred lines developed for tropical-highlands and highland transition maize agro-ecologies using microsatellite (SSR) markers. A total of 36 white-grained maize inbred lines, including 30 QPM and six non-QPM were genotyped using 26 simple sequence repeat (SSR) markers. Estimates of the average number of alleles per locus, gene diversity, and polymorphism information content (PIC) were 3.8, 0.53, and 0.49, respectively. Pairwise Euclidean genetic distances ranged from 0.11 to 1.10 with mean of 0.74.Three major genetic groups were also identified, which are generally consistent with available pedigree information except a few discrepancies. Therefore, the genetic classification using the SSR markers could assist in strategic QPM breeding for tropical-highland and highland transition agro-ecologies. The outputs also form the basis for future studies aimed at confirming heterotic groups and identifying any new heterotic patterns that can emerge in the highland QPM germplasm.&nbsp

In Ethiopia, heavy losses to stored maize are inflicted by various insect pests including Sitophilus weevils and Sitotroga cereallela. This study was conducted to determine the combining ability of five introduced inbred lines in agronomic traits and maize weevil resistance by crossing them with three testers using line × tester mating system. These crosses were then evaluated in tri-plicated randomized complete blocks at Bako Agricultural Research Center in 2003. Samples (50 g) of the F2 full-sib grain of the genotypes were further tested for weevil resistance under a no-choice laboratory environment. Mean squares due to general (GCA) and specific (SCA) combining ability were significant for most of the agronomic traits. However, GCA mean squares predominated in all weevil resistance traits. The lines varied in their GCA effects for the various agronomic traits considered. However, all of them were found to be poor general combiners for grain yield, although certain crosses gave acceptable yield. The lines SZSYNA99-F2-133-2-3, SZSYNA99-F2-33-4-1, SZSYNA99-F2-33-4-2 and SZSYNB99-F2-98-4-3 exhibited desirable GCA effects for most of the resistance traits. Overall, this study suggested the existence of heritable weevil resistance quantitative traits that can be used in weevil resistance breeding programs.&nbsp

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., Journal of Science and Sustainable Development, Vol. 8 No. 1 (2020)

Development of inbred lines is a routine activity in hybrid maize breeding program.Understanding the relative importance of general (GCA) and specific (SCA) combining ability effects fordifferent traits of newly developed maize lines is of paramount importance to design future breedingstrategies for the development of hybrid. There are several types of mating designs available to study thecombining abilities of maize inbred lines, of which line x tester mating scheme is one used to determinethe combining abilities and also to categorize the lines into heterotic groups. The objectives of the studywere, therefore, to estimate GCA and SCA of newly developed highland maize lines using line x testermating design, to identify best promising hybrid crosses with desirable traits for further breeding andcultivar development, and to identify the heterotic groups of the lines involved in the crosses. Twelvelines and four testers were involved in the study. A total of 48 testcrosses along with two checks weremade available for evaluation across locations. An alpha lattice design (10x5) with two replications at eachlocation was used. Two lines (L6 and L5) showed highly significant and positive GCA effects for grainyield. Besides, L6 also revealed positive GCA effects for the other yield related traits such as number ofears per plant (NEPP), number of rows per ear (NRPE), number of kernels per row (NKPR) and eardiameter (ED). On the other hand, crosses L7XT2, L8xT4, and L9xT1 had positive and significant SCAeffects for grain yield. The lines and crosses with positive and significant GCA and SCA effects,respectively; could be selected for use in highland maize hybrid or/and synthetic cultivar development.The testers clearly categorized L3 and L6 into their respective heterotic groups in a similar pattern unlikethe other lines which requires the application of molecular markers for further verification.