Integrated management of Striga gesnerioides in cowpea using resistant varieties, improved crop nutrition and rhizobium inoculants

Background Cowpea is a grain legume of major importance in sub-Saharan Africa where it is cultivated by smallholder farmers on poor soils and production is often constrained by the parasitic weed Striga gesnerioides . Method Experiments were conducted to assess the potential of rhizobium inoculation to mitigate Striga infection and increase cowpea productivity. We infested soils with S. gesnerioides and assessed the impact of treatments combining cowpea genotypes and bradyrhizobium inoculation on Striga dynamics and cowpea yield. In total, 20 cowpea genotypes were included, of which nine were resistant to Striga and 11 were susceptible. In the first experiment these were factorially combined with three inoculation options (two bradyrhizobium strains USDA3384 and IRJ2180A, and uninoculated control) in a screen-house using potted sterile soils. Second, the same trial was repeated in the field with basal phosphorus applied at sowing and a fourth treatment of fertilizer-N (urea) included testing whether N was limiting cowpea growth. The field trial also included a separate treatment with no input that served as a negative check. Result Significant genotype x treatment interactions were observed in nodule counts, Striga attachment, emergence, and cowpea shoot growth in the screen-house. There were few nodules across all cowpea lines. Striga counts were the lowest for resistant varieties with no emerged plants. Rhizobial inoculants depressed Striga counts with consistent differences across cowpea genotypes. Inoculation with IRJ2180A performed the best against Striga attachment in resistant genotypes, and against Striga emergence in susceptible genotypes. In the field trial, cowpea grown without inputs had the least number of nodules. The genotype x treatment interaction was significant: resistant cowpea genotypes were free of emerged Striga while there was much more Striga emergence without input addition with susceptible genotypes. A significant genotype x treatment interaction was observed on cowpea grain yield. Yield response to inoculation was clearest with resistant genotypes inoculated with the strain IRJ2180A. Conclusion The integrated use of Striga -resistant cowpea lines, basal phosphorus fertilizer and elite bradyrhizobium inoculants is a promising approach to mitigate Striga infection and increase cowpea productivity.