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Abstract Nitrogen (N) is an important nutrient element needed by cassava for optimum yield and it is a vital component of nucleotides (nucleic acids), enzymes, amino acids (proteins), chlorophyll molecules and hormones, among other essential compounds required for growth and development of cassava. Nitrogen stress is a major cassava production constraint, the study aimed to examine genotype by environment interaction (GEI) effects and fresh root yield stability of 203 diverse cassava clones to identify genotypes with stable performance under low and optimum nitrogen regimes across environments using AMMI and GGE biplot analysis. Experiments were conducted using an augmented block design with three replications for two years in three locations in Nigeria. There were significant differences (p

Genetic diversity is a crucial aspect of plant breeding, as it provides the foundation for crop improvement. This study aimed to evaluate the genetic diversity and identify unique genotypes within the cassava germplasm in Togo. To achieve this, 192 cassava accessions from major growing regions were genotyped using 28 genome-wide SNP markers. The results showed that 12 markers were moderately informative, having PIC values between 0.25–0.50, while two markers were less informative, having PIC values below 0.25. The PIC values ranged from 0.11– - 0.37, and major allele frequencies ranged from 0.49–- 0.88. Heterozygosity ranged from 0.09– 0.62, and gene diversity ranged from 0.11–0.50. The germplasm exhibited a moderate genetic diversity level, showing an average expected heterozygosity of 0.42 and observed heterozygosity of 0.50. Hierarchical clustering and PCA identified three distinct genotypic groups. Additionally, 60 duplicate accessions were detected based on SNP profiles. AMOVA analysis indicated that the observed genetic diversity was primarily due to differences between accessions. The core cassava set developed in this study will serve as an invaluable resource for future genomic research and strategies for the improvement of the crop.

Maize (Zea mays L.) is one of the most widely cultivated grain crops globally. In sub-Saharan Africa (SSA), it plays an important role in ensuring both food and income security for smallholder farmers. This study was conducted to (i) assess the performances of testcross hybrids constituted from maize lethal necrosis (MLN) tolerant doubled haploid (DH) lines under various management conditions; (ii) estimate the combining ability effects and determine the nature of gene action in the DH lines; and (iii) identify DH lines and testcross hybrids for resistance to MLN, high grain yield, and other important traits. Eleven DH lines were crossed with 11 single-cross testers using the line-by-tester mating design, and 115 successful testcross hybrids were generated. These hybrids, along with five commercial check hybrids, were evaluated across four optimum management conditions, two MLN artificial inoculations, and one managed drought environment in Kenya. Under each management condition, the effects of genotypes, environments, and genotype-by-environment interactions were significant for grain yield (GY) and most other traits. Hybrids T1/L3, T10/L3, and T11/L3 exhibited higher grain yields under at least two management conditions. A combining ability analysis revealed that additive gene effects were more important than non-additive effects for GY and most other traits, except for leaf senescence (SEN) and MLN disease severity score. DH line L3 exhibited a desirable general combining ability (GCA) effect for GY, while L5 was the best general combiner for anthesis date (AD) and plant height (PH) across all management conditions. DH lines L2, L6, and L7 showed negative GCA effects for MLN disease severity. Single-cross testers T11 and T10 were good general combiners for GY under all management conditions. Hybrids T2/L11, T9/L10, and T2/L10 demonstrated high specific combining ability (SCA) effects for GY under all conditions. This study identified DH lines and testers with favorable GCA effects for grain yield, MLN resistance, and other agronomic traits that can be used in breeding programs to develop high-yielding and MLN-resistant maize varieties. Better-performing testcross hybrids identified in the current study could be verified through on-farm testing and released for commercial production to replace MLN-susceptible, low-yield hybrids grown in the target ecologies.

Cassava productivity is constrained by low soil nitrogen, which is predominant in most cassava-growing regions in the tropics and subtropical agroecology. Improving the low nitrogen tolerance of cassava has become an important breeding objective. The current study aimed to develop cassava varieties with improved nitrogen use efficiency by identifying genomic regions and candidate genes linked to nitrogen use efficiency in cassava. A genome-wide association study (GWAS) was performed using the Genome Association and Prediction Integrated Tool (GAPIT). A panel of 265 diverse cassava genotypes was phenotyped for 10 physiological and agronomic traits under optimum and low-nitrogen regimes. Whole-genome genotyping of these cassava cloneswas performed using the Diversity Arrays Technology (DArTseq) sequencing platform. A total of 68,814 single nucleotide polymorphisms (SNPs) were identified, which were spread across the entire 18 chromosomes of the cassava genome, of which 52 SNPs at various densities were found to be associated with nitrogen use efficiency in cassava and other yield-related traits. The putative genes identified through GWAS, especially those with significant associated SNP markers for NUE and related traits have the potential, if deployed appropriately, to develop cassava varieties with improved nitrogen use efficiency, which would translate to a reduction in the economic and environmental cost of cassava production.

Biofortification of staple food stands as one of the most reliable methods of alleviating vitamin A deficiency (VAD). Evidence suggests that introducing provitamin A carotenoid (pVAC) cassava into the diets of preschool and primary school children in East Africa has led to improvements in their retinol levels. Notably, Kenya and Uganda have initiated cassava biofortification programs in the region. These efforts involve the assembly and characterization of pVAC cassava germplasm, alongside the development of essential tools such as genomic prediction (GP) models and molecular markers for accelerating genetic gains in the biofortification programs. However, several challenges have emerged, including a negative correlation between carotenoid content and dry matter content in cassava roots, diseases, the absence of affordable high-throughput phenotyping methods, poor cassava flowering, poor pollen viability, low capacity in bioinformatics analyses, degradation of carotenoids during processing, and inadequate germplasm conservation facilities. To address these hurdles, cassava breeding programs in the region require enhanced infrastructure and human capacity to optimize efficiency in cassava biofortification with pVACs.

Parasitism of crop plants by Striga species is a major constraint in the savannah zones of West Africa. A germplasm collection comprised of 240 accessions of pearl millet was screened under natural Striga hermonthica infestation to identify sources of Striga resistance. Data were collected at different time points, specifically at 70, 90 and 140 days after planting for Striga count, Striga vigour and Striga severity. Number of panicles, panicle weight and Grain yield were also measured. The results revealed significant variation in the resistance of pearl millet genotypes to Striga. Fifteen genotypes identified as the most resistant were free of emerged Striga shoots, 10 genotypes supported 14 Striga shoots but with appreciable yield and 15 genotypes with 1-4 Striga shoots and low grain yield. Principal Component and cluster analyses grouped these genotypes into 3 main clusters medium yielding tolerant to Striga, low yielding susceptible to Striga and medium to high yielding resistant to Striga. The high level of resistance observed in some breeding lines enabled the selection of suitable parents for population development.