Soybean [Glycine max (L.) Merrill] is an important crop in southern Africa where it is cultivated in a wide range of agro-ecologies. Both spatial and seasonal variability is high in the region. As a result, breeders aim to release varieties with a fine balance of high productivity potential and stability. Genotype × environment interaction (GEI) limits the selection of superior genotypes in heterogeneous environments consequently slowing down breeding progress. This study determined the magnitude of GEI effects and genotype superiority index of soybean genotypes of different ages across three countries in southern Africa. Forty-two soybean genotypes that were released between 1966 and 2013 were evaluated for two seasons at thirteen diverse locations across the three countries. Additive main effects and multiplicative interaction (AMMI) and genotype superiority index tools were used to analyse both productivity and stability performance of these genotypes. The AMMI analysis showed that grain yield variation due to genotypes, environments main effects and GEI were highly significant (p < 0.001). Environments explained the greatest proportion (77%) of the total treatment sum of squares followed by GEI (17.4%) and genotypes (5.6%), justifying the need for multi-environmental trials over many seasons in this region. The two methods were useful in discriminating and identifying common productive and stable genotypes of different ages. The top four high-yielding (>5.0 tha⁻¹) genotypes displayed both stability and genotype superiority index. These findings have important implications for soybean genotype recommendations, breeding progress, and strategy.

Maize production in sub-Saharan Africa is severely constrained by Striga hermonthica infestation, a parasitic weed that causes substantial yield losses in farmers’ fields. Therefore, developing maize genotypes that combine high grain yield with resistance or tolerance to Striga infestation is essential for improving smallholder farmers’ productivity and livelihoods. In this study, we evaluated the response of selected top-cross maize hybrids to Striga hermonthica infestation and identified high-yielding hybrids suitable for cultivation in affected environments. Thirty-two top-cross hybrids and eight commercial checks were evaluated under artificial Striga-infested and non-infested conditions across four environments in Nigeria using a 10 × 4 alpha-lattice design with two replications. Significant genotypic differences in grain yield and Striga-related traits were observed among the hybrids under both conditions. The variance attributable to general combining ability (GCA) was greater than that due to specific combining ability (SCA) for grain yield and Striga damage parameters, indicating that additive gene effects predominantly control the inheritance of these traits. One parental line (TZISTR2014) was identified as a desirable general combiner for improved grain yield, whereas TZISTR1872 was identified as a good combiner for reduced Striga emergence count. Four top-cross hybrids (FAWSYN-1/TZISTR2014, FAWSYN-1/TZISTR2024, FAWSYN-2/TZISTR1318, and FAWSYN-1/IITAZI2305), together with two commercial checks (Oba Super 9 and Oba Super 11), exhibited superior grain yield and Striga infestation tolerance. Among these, FAWSYN-1/TZISTR2014 showed reduced Striga emergence, whereas FAWSYN-1/IITAZI2305, FAWSYN-1/TZISTR2024, and FAWSYN-2/TZISTR1318 displayed favorable responses to Striga damage. These hybrids represent valuable genetic resources for developing improved populations and extracting inbred lines for producing high-yielding Striga-resistant maize hybrids in sub-Saharan Africa.

Background: Understanding the genetic diversity and population structure of maize inbred lines is fundamental for effective hybrid development and strategic heterosis exploitation. The objective of this study was to refine and validate heterotic groups within a diverse collection of extra-early and early maturing tropical yellow and orange maize inbred lines. A total of 1,437 elite tropical yellow and orange maize inbred lines spanning early and extra-early maturing groups were genotyped using a panel of 3,305 DArTag SNP markers. In addition, the study evaluated 280 hybrids comprising 276 hybrids (from 214 inbred lines crossed with four standard testers) and four commercial checks. The yield performance trials used a 14 × 20 alpha-lattice design with two replicates over two years. Results: Marker-based diversity analysis revealed average marker polymorphism of 0.328, minor allele frequency of 0.265, and expected heterozygosity of 0.315. Principal component analysis (PCA), discriminant analysis of principal components (DAPC), and ancestral admixture analysis revealed three genetic clusters, while phylogenetic analysis supported the existence of two major clusters with groups one and three from DAPC and admixture methods combined into a single phylogenetic group. Several sub-groups were identified within the main genetic pools and maturity rather than kernel color was the major driver of these sub-groups. For operational ease in breeding applications, the lines were assigned to two major heterotic groups. The average performance of the hybrid for grain yield and heterosis estimates from between maturity-based heterotic subgroups were consistently and significantly ( p < 0.001) higher than those from within maturity-based heterotic subgroups. Conclusion: These results provide a robust framework for parental line selection, heterotic grouping, and hybrid breeding strategies, facilitating the development of extra-early and early superior yellow/orange maize hybrids adapted to tropical environments.

The stem borer ( Chilo partellus Swinhoe) causes 12%–17% yield losses in the field, while additional 15%–30% grain losses are caused by the maize weevil ( Sitophilus zeamais Motschulsky) in storage across sub-Saharan Africa. Despite advances in host plant resistance, maize hybrids with combined resistance to both insects remain unknown. The objective of this study was to combine resistance to stem borer and maize weevil in elite maize germplasm through breeding. Forty maize inbred lines were divided into groups of five lines based on insect resistance levels. Eight sets of 25 hybrids each were generated using a 5 x 5 North Carolina II mating design within each set. The resulting 190 F ₁ hybrids with sufficient seeds were evaluated for grain yield and stem borer damage across four environments in Kenya. Resistance to Chilo partellus was assessed under field conditions, while post-harvest grain was screened for Sitophilus zeamais resistance under controlled laboratory conditions. The results showed significant differences ( p ≤ 0.05) among hybrids for grain yield and insect resistance parameters such as leaf damage, grain weight loss and undamaged kernels. General combining ability effects associated with both male and female parents were highly significant ( p ≤ 0.01) for all traits indicating involvement of additive gene effects. Specific combining ability (SCA) effects were significant for grain yield under protected and insect infested conditions, and undamaged kernels indicating the role of non-additive gene effects for these traits. However, the SCA effects were not significant for leaf damage and grain weight loss suggesting that non-additive gene effects did not play a major role for these traits. These findings imply that heterosis can be exploited to improve hybrids for grain yield under both insect infested and protected conditions. Approximately 8% of the hybrids exhibited resistance to stem borer, while several showed reduced grain weight losses due to maize weevil damage. Grain yield advantage (standard heterosis) ranged from 26% to 41% over commercial check hybrids, indicating that breeding for combined resistance has potential for improving both yield and insect resistance. Four hybrids (17 x 40, 19 x 40, 3 x 25, 2 x 23) combined dual resistance with superior grain yield demonstrating feasibility of developing resilient maize varieties.

Knowledge of the genetic diversity of the available germplasm is an important foundation for crop conservation, management, and improvement. Successful breeding strategies rely on a sound understanding of the genetic diversity of the crop germplasm. This study was conducted to evaluate and compare the genetic diversity of 49 soybean [Glycine max (L.) Merrill] genotypes using SSR markers as well as to evaluate parental potential of these genotypes in cultivar improvement. The bulk of the genotypes were developed in the national soybean breeding program in Zimbabwe between 1940 and 2013. The genetic diversity and relatedness were estimated using 30 SSR markers and produced 5 clusters that generally matched the pedigree information of the germplasm. The SSR analysis detected a total of 135 alleles. The polymorphic information content ranged from 0.10 to 0.77 with a mean of 0.45. The SSR primer, Satt012 was the most informative. The SSR marker analysis showed a wide genetic diversity in the germplasm. To date, there are no reports regarding the genetic diversity analysis of soybean germplasm in Zimbabwe. The genotypes, EL41 and EL7; EL41 and EL1; as well as EL41 and EL42 were the most divergent thus, indicating their potential use as parental lines in the genetic improvement of soybean in the region.

Aspergillus ear rot (ear rot) and aflatoxin contamination, caused mainly by Aspergillus flavus , threaten maize productivity, grain quality, and food safety in tropical and sub-tropical regions. Although significant breeding progress has been made, selection for resistance remains challenging due to environmental conditions, genotype × environment interaction (G×E), low heritability of resistance traits, and the need to simultaneously improve productivity. The objectives of this study were to: assess the effect of genotype, environment and G×E, examine trait relationships, and identify superior maize hybrids with favourable multi-trait performance. Eighty-three maize inbred lines were crossed with two testers using a line × tester mating design. The resultant 166 testcrosses and six checks were evaluated across four environments with two replications in each environment under artificial inoculation using a highly toxigenic A. flavus isolate (La3228). Data were analysed using linear mixed models, with variance components estimated by REML. Environmental effects were significant for aflatoxin accumulation and ear rot ( p ≤ 0.05), while hybrids differed significantly for grain yield and ear rot ( p ≤ 0.01). There was no significant G×E interaction for grain yield, aflatoxin accumulation and ear rot ( p ≥ 0.05). Broad-sense heritability estimate was high for grain yield (H ² = 0.62), moderate for ear rot (H ² = 0.36) and low for aflatoxin (H ² = 0.22), indicating strong environmental influence on the expression of the resistance-related traits. Grain yield was not significantly correlated with aflatoxin accumulation (r = 0.08), suggesting that selection for grain yield may be independent of aflatoxin accumulation. However, grain yield was significantly and negatively correlated with ear rot (r = -0.20*). The first two principal components of the genotype plus genotype × environment (GGE) biplot explained 76.4% of the total variation among the selected hybrids and identified two mega-environments, revealing differential adaptation among hybrids. The sequential application of multi-trait genotype–ideotype distance index (MGIDI) and GGE biplot identified five testcrosses, En80, En74, En102, En157, and En65 combining competitive grain yield, favourable stability, and resistance-related traits. These hybrids are promising for further multi-environment evaluation for their potential contribution to the development of maize hybrids with improved productivity and reduced aflatoxin accumulation in tropical and sub-tropical regions.