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Testing and identification of high-yielding and stable hybrids adapted to contrasting environments is crucial for sustainable maize (Zea mays L.) production in sub-Saharan Africa. The objectives of this study were to (i) assess the yield response of 150 single-cross hybrids under low soil nitrogen (low-N), Striga-infested and optimal growing environments, and (ii) identify the most suitable environments for the selection of superior and stable hybrids. The 150 hybrids were derived from 30 inbred parents via North Carolina design II mating scheme. They were tested, together with six checks, in a 13 × 12 alpha lattice design with two replications across 10 test environments in 2016 and 2017. Genotype by environment interaction was significant for yield, with high repeatability (0.70) across the test environments. Test environments KWDS-LN-16 and KWDS-OPT-16 were found to be the ideal test environments for selecting superior hybrids. About 62% of the hybrids were stable across environments. Hybrids TZEI 3A × TZdEI 192, TZdEI 216 × TZEI 3A and TZEI 379 × TZdEI 272 were identified as high yielding and most stable across environments. These outstanding hybrids with tolerance to both Striga and low-N should be further tested extensively on-farm for potential release in Ghana and other West African countries.

Maize is a major staple food in sub-Saharan Africa. However, due to the threats posed by biotic and abiotic constraints to its production, it is a prerequisite to conserve germplasm with diverse genetic background and to seek for favourable genotypes with such background for improvement of superior genotypes. This study assessed the diversity of 70 white maize populations developed at CSIR-Savanna Agricultural Research Institute with resistance/tolerance to drought and low soil nitrogen (Low-N) using 31 SSR markers. A total of 288 alleles were detected among the germplasm used with a range of 4 to 17 alleles per locus and an average allele number of 9.60 alleles per locus. Polymorphic Information Content values for the SSR markers ranged from 0.32 to 0.85 with a mean value of 0.68. The average heterozygosity obtained from the markers was 0.54 and gene diversity ranged from 0.35 to 0.87 with a mean gene diversity value of 0.71 indicating a high level of polymorphism among the populations. Clustering based on Jaccard's similarity coefficient and an Unweighted Pair Group Method with Arithmetic Mean (UPGMA) revealed 5 clusters for the 70 populations. Evanno method for population structure clustering further revealed two sub-populations. Sub-population 1 was more genetically diverse with an Fst value of 0.18 than sub-population 2 which recorded an Fst value of 0.013. These results indicated that the SSR used were very polymorphic for diversity studies. Also, the studied maize populations are diverse and heterozygous, making them ideal source populations for extraction of drought and low-N tolerant inbred lines. Keywords: Drought, Polymorphic, Diversity, Microsatellite, Heterozygosity

Maize is a food security crop cultivated in the African savannas that are vulnerable to the occurrence of drought stress and Striga hermonthica infestation. The co-occurrence of these stresses can severely damage crop growth and productivity of maize. Until recently, maize breeding in International Institute of Tropical Agriculture (IITA) has focused on the development of either drought tolerant or S. hermonthica resistant germplasm using independent screening protocols. The present study was therefore conducted to examine the extent to which maize hybrids simultaneously expressing resistance to S. hermonthica and tolerance to drought (DTSTR) could be developed through sequential selection of parental lines using the two screening protocols. Regional trials involving 77 DTSTR and 22 commercial benchmark hybrids (STR and non-DTSTR) were then conducted under Striga-infested and non-infested conditions, managed drought stress and fully irrigated conditions as well as in multiple rainfed environments for 5 years. The observed yield reductions of 61% under managed drought stress and 23% under Striga-infestation created desirable stress levels leading to the detection of significant differences in grain yield among hybrids at individual stress and non-stress conditions. On average, the DTSTR hybrids out-yielded the STR and non-DTSTR commercial hybrids by 13–19% under managed drought stress and fully irrigated conditions and by −4 to 70% under Striga-infested and non-infested conditions. Among the DTSTR hybrids included in the regional trials, 33 were high yielders with better adaptability across environments under all stressful and non-stressful testing conditions. Twenty-four of the 33 DTSTR hybrids also yielded well across diverse rainfed environments. The genetic correlations of grain yield under managed drought stress with yield under Striga-infestation and multiple rainfed environments were 0.51 and 0.57, respectively. Also, a genetic correlation between yields under Striga-infestation with that recorded in multiple rainfed environments was 0.58. These results suggest that the sequential selection scheme offers an opportunity to accumulate desirable stress-related traits in parents contributing to superior agronomic performance in hybrids across stressful and diverse rainfed field environments that are commonly encountered in the tropical savannas of Africa.

Fall armyworm (FAW), Spodoptera frugiperda (J.E. Smith), was first detected in Africa in 2016. Efforts at controlling it have been challenged by the many unknowns about this invasive insect. The population dynamics of FAW moths and the damage caused by the larvae were studied in maize fields over two successive seasons in northern Ghana. Pheromone traps were deployed in sole maize fields located in Northern (NR), Upper East (UER) and Upper West (UWR) regions to assess male moth population over time. Data on damage to maize by the larvae as well as climatic variables were also recorded. A total of 2601 FAW moths were captured over the two seasons from the three regions. In general, catches increased steadily from time of emergence (i.e., 12.2 ± 1.4 and 14.4 ± 2.6 moths in July 2017 and 2018, respectively) and peaked when the plants were growing into the reproductive stage (i.e., 13.9 ± 2.2 and 56.0 ± 14.9 moths in August 2017 and 2018, respectively); afterwards catches declined significantly. There were no significant differences between regions in both years for mean their moth catches. Damage to maize was significantly higher in 2017 (4.8 ± 0.4) than in 2018 (2.4 ± 0.3) (P = 0.005). This variable correlated positively with FAW larval abundance. Rainfall was the only climatic variable that influenced moth abundance significantly and positively in all three regions in both years; except for 2018 in UER. Thus, management of FAW in northern Ghana and locations with similar agro-ecologies must be from emergence to the tasselling stage, as well as periods of increased precipitation.

Maize plays a crucial role in combating food insecurity in Ghana due to its high yield potential and wide adaptability. Thirty five intermediate maturing maize hybrids were evaluated at eight locations in Ghana for two years (i) to determine grain yield performance, stability and adatability, (ii) to determine the representativeness and discriminating ability of the test locations and (iii) identify core testing sites for selection of superior maize hybrids. Genotype, environment and genotype × environment interactions were significant (p