Combining ability, heterosis and heritability of agronomic traits and resistance to maize streak virus in maize inbred lines
Maize is an important cereal crop in Sub-Saharan Africa which contributes substantial portion to the diet of millions of people. The production of maize is being affected by maize streak virus disease (MSVD); an economically important foliar disease, thereby causing significant grain yield losses in farmers’ fields. In Ghana, re-occurrence of the disease has been reported in several regions, therefore, necessitating the development of resistant hybrids which is the most sustainable and economical management option. The objectives of the study were to identify parents and hybrids that combine MSVD resistance with high yield, and also to determine the influence of maternal effect on the inheritance of MSVD resistance. Five parental inbred lines namely; TZEI-4, TZEI-7, TZEI-22, TZEI-31 and TZEI-157 were crossed in a full diallel mating design during the major season of 2015. The resulting F1 hybrids were evaluated under natural and artificial infestations during the minor and major seasons of 2015/2016 using 9 x 3 alpha-lattice design with three replications. Diagnosis of the viral disease using Polymerase Chain Reaction confirmed the presence of maize streak virus in the 27 genotypes evaluated. ANOVA for diallel crosses across environments revealed that general combining ability (GCA) and specific combining ability (SCA) mean squares were significant for MSVD severity mean score and most of the agronomic traits. Maternal effect had no significant contribution to the inheritance of MSVD resistance. GCA by environment (P<0.01) and SCA by environment (P<0.001) interactions mean squares were significant for MSVD severity mean score indicating that the disease pressure was higher under artificial infestation. Additive gene effect was preponderant for MSVD severity mean score, total leaf count, plant aspect and ear aspect whereas, the expression of other traits was influenced by non-additive gene effect. GCA effects revealed that inbred lines TZEI-7 and TZEI-22 were resistant to MSVD and could be good combiners for grain yield in addition to TZEI-31 and TZEI-157. Hybrids TZEI-4*TZEI-22 and TZEI-4*TZEI-31 showed resistance to MSVD as revealed by their SCA effects and heterotic values. TZEI-7*TZEI-157, TZEI-31*TZEI-157, TZEI-22*TZEI-157 and TZEI-4*TZEI-22 had positive and significant SCA effect, mid-parent heterosis and high parent heterosis for grain yield. The narrow sense heritability estimated for MSVD severity mean score, total leaf count and plant aspect were 55.3, 40.44 and 36.37 % respectively, while broad sense heritability ranged from approximately 54 to 84 % for all the measured traits. MSVD severity mean score correlated negatively and significantly (P<0.01) with total leaf count, plant height and 100-grain weight. Response to selection can be achieved for MSVD resistance combined with high grain yield if selection is based on MSVD severity mean score, total leaf count and plant aspect. Total leaf count, ear leaf area, plant height and 100-grain weight correlated significantly (P<0.001) and positively with grain yield. Promising hybrids TZEI-4*TZEI-22, TZEI-22*TZEI-157, TZEI-7*TZEI-157 and TZEI-31*TZEI-157 identified in this study should be further tested in multi-locations across Ghana to determine their stability and adaptability.
A thesis submitted to The Department of Crop and Soil Sciences, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana in partial fulfillment of the requirements for the degree of Master of Philosophy in Plant Breeding,