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Early leaf spot (ELS) disease, caused by Cercospora arachidicola S. Hori, severely affects groundnut (Arachis hypogaea L.) production worldwide. Breeding for resistant varieties using conventional breeding is difficult because multiple genes control the resistance and heritability is moderate. Our objective was to identify marker-trait associations (MTAs) for ELS resistance in a mini-core collection of 168 accessions. The accessions were genotyped using diversity array technology (DArTseq™) and phenotyped at two locations with and without inoculation. Two types of DArTseq markers were scored; Silico DArT markers and biallelic single nucleotide polymorphism (SNP) markers. Genotype effects were significant for both ELS and pod weight (PW), with several accessions showing good levels for resistance. The heritability of ELS was moderate (0.37 to 0.64), whereas heritability for PW was low (0.10 to 0.18). The DArTseq generated 3592 biallelic SNP markers and 15,237 dominant silico markers. The distribution of the biallelic and dominant markers across the genome shows that chromosomes B04 and A04 had the highest number of markers. The MTA analysis revealed 25 significant (p < 0.001) MTAs. One MTA for ELS was found across treatments and rating dates and may be suitable for marker-assisted selection upon validation. No MTA for PW was repeatable. The germplasm and markers identified in this study can serve as useful genomic resources to initiate marker-assisted selection and trait introgression for ELS resistance in groundnut. [ABSTRACT FROM AUTHOR]

Background: The genetic yield potential of groundnut (Arachis hypogaea L.) has been continuously challenged by several diseases including early leaf spot (ELS). Methods: In the current study, we evaluated groundnut mini core collections under artificial and natural disease epiphytotics in six environments to identify stable elite sources for ELS resistance and pod yield. Mixed model analysis was done to adequately capture the variance component as a result of genotype (G), environment (E) and G x E interaction (GEI). Result: Highly significant (p <0.001) effects for G and GEI on ELS and pod weight were observed. The parametric and non-parametric stability models ranked the genotype differently for their stability to ELS. The GGE biplot identified ICG 1519 as a stable genotype for the ELS resistance. For pod weight, ICG 8896 and ICG 7897 were consistently stable from all the stability models including the GGE biplot. ICG 9449 and ICG 4540 were identified as stable genotypes for both ELS and pod weight. These elite sources of ELS resistance identified in the current study will be useful in the development and deployment of groundnut varieties with resistance to ELS and high pod yielding potentials. [ABSTRACT FROM AUTHOR]

Grain yields of cowpea [Vigna unguiculata (L.) Walp.] in the Nigerian savannas are low even with the cultivation of improved varieties. The recommended spacing for cowpea is 75 × 20 cm with two seeds planted per stand. This corresponds to plant population of 133333 plants ha−1, which may not be sufficient for optimal cowpea yield. Field experiments were conducted to determine plant density effects on cowpea performance in the Northern Guinea and the Sudan savannas of Nigeria and also to determine if genotypes varied in their response to plant density. Four cowpea varieties with contrasting maturity duration were planted in single, double and triple rows on ridges spaced 75 cm apart to achieve corresponding densities of 133333, 266666 and 400000 plants ha−1, respectively. Plant densities of 266666 and 400000 plants ha−1 gave higher crop performance in terms of light interception, biomass production, yield and yield components for all cowpea varieties. Yield increases were related largely to increased pod and seed production but the effect of seed size on yield was relatively minor. Our results provide evidence that the current density of 133333 plants ha−1 used by farmers is not optimum for cowpea production. Smallholder farmers can increase cowpea grain and fodder yields if they use a density of 266666 plants ha−1 in cowpea cultivation. Further yield increases when cowpea is planted at 400000 plants ha−1 may not be sufficient to offset the cost of seed. [ABSTRACT FROM PUBLISHER]

Soybean (Glycine max) is a major cash crop in the savannas of Nigeria although productivity is typically constrained by poor soil fertility. The objective of this research was to determine the interactive effect of N and P on soybean productivity in the northern Guinea and Sudan savannas of northeast Nigeria. Experiments were conducted using locally adapted early and late maturing cultivars. Two rates of N and three rates of P fertilizer were also compared at both sites over two years. At both sites, pods plant−1 and seed yield were higher in 2006 than in 2007, possibly due to better rainfall distribution in 2006. Nitrogen fertilizer had no significant effect on seed yield or pods plant−1. Application of P fertilizer increased pods plant−1 by 40–66%. Averaged across site and year, seed yield with no P was 1057.2 kg ha−1 while yield with 20 and 40 kg ha−1 P were 1941.0 kg ha−1 and 2371.5 kg ha−1, respectively. No significant interaction effect between N and P fertilizer on seed yield and pods plant−1 was observed. The late maturing cultivar yielded less than the earlier maturity group cultivar in 2007 likely due to moisture stress. For optimum seed yield 40 kg of P fertilizer ha−1 is recommended for soybean production in both locations. Our results suggest that N fertilizer is not critical for soybean production in this area. [ABSTRACT FROM PUBLISHER]