BREEDING MAIZE (ZEA MAYS L.) HYBRIDS WITH COMBINED TOLERANCE TO STRIGA HERMONTHICA AND LOW SOIL NITROGEN FOR THE NORTHERN SAVANNA ZONES OF GHANA

Maize is an important staple crop widely produced and consumed in West and Central Africa (WCA). Low soil nitrogen (low-N), recurrent drought and Striga hermonthica infestation are major constraints to maize production and productivity in WCA. The specific objectives of this study were to (i) determine genetic diversity among 100 selected set of maize inbred lines using Simple Sequence Repeat (SSR) and Single Nucleotide Polymorphism (SNP) markers (ii) classify the selected set of inbred lines into heterotic groups using the general combining ability effect of multiple traits (HGCAMT) method, SSR and SNP markers, and to compare effectiveness of the different methods in grouping the inbred lines, (iii) determine the combining ability and heterosis for grain yield and agronomic traits of the selected set of inbred lines under Striga infestation, low-N and optimal growing conditions, (iv) determine the grain yield potential and yield stability of hybrids derived from the selected inbred lines under Striga infestation, low-N and optimal growing conditions. Substantial genetic and phenotypic variability existed among the inbred lines used in this study for grain yield, Striga resistance/tolerance and low-N tolerance. Although SSR markers used in this study were highly informative, the use of large number of SNP markers made the SNP comparable with the SSR for genetic diversity analysis, and better than SSR in cluster and population structure analyses. Genetic analysis of 150 hybrids derived from the North Carolina Mating Design II revealed significant differences among the hybrids for grain yield, Striga resistance and low-N tolerance. General combining ability and SCA mean squares were significant for grain yield and most traits under optimal, Striga-infested and low-N environments and across environments, indicating that both additive and non-additive gene actions were important in the inheritance of the traits. The inheritance of grain yield under low-N and across environments were controlled largely by additive gene action, while the inheritance of grain yield under optimal and Striga-infested environments were controlled largely by non-additive gene action. Non-additive gene action largely modulated the inheritance of almost all traits measured under Striga-infested environments, except for Striga damage syndrome rating at 8 WAP. The SNP genetic distance based heterotic grouping method was identified as the most efficient in grouping the inbred lines into heterotic groups. The yield response and stability analyses of the 150 hybrids and six local checks over 10 contrasting environments indicated that 62% of the hybrids had average stability across environments, while 8% had above average stability and were adapted specifically to either Striga-infested or low-N environments. The hybrids TZdEI 215 x TZdEI 192, TZEI 378 x TZdEI 215 and TZEI 3A x TZdEI 192 were the highest yielding and most stable across environments. They are recommended for further testing and commercialization in the savanna zones of Ghana and other countries in WCA.

Source: KNUST