Pathogen-Microbiome Interactions in the Rhizosphere of Maize Under Striga hermonthica-Fusarium Co-Stress in the Savanna Zone of Nigeria

Maize (Zea mays) in Nigeria's savanna zone is simultaneously challenged by the root parasitic weed Striga hermonthica and soilborne Fusarium pathogens, yet the interaction between these stressors and their combined effects on rhizosphere microbiome structure and plant health outcomes remain unexplored. Understanding pathogen-microbiome interactions under co-stress conditions represents a significant emerging research frontier with direct implications for integrated management design. This doctoral research investigates the tripartite interactions between Striga hermonthica, Fusarium verticillioides, and the rhizosphere microbiome in maize under savanna conditions across experimental sites in Kaduna, Niger, and Kwara States. The research combines: controlled greenhouse inoculation experiments varying single and co-stress conditions; 16S rRNA and ITS amplicon metagenomic profiling of rhizosphere soil communities under each stress condition at tillering and tasselling stages; untargeted metabolomic profiling of root exudates associated with Striga-stimulated strigolactone signalling and Fusarium infection responses; and statistical mediation analysis testing whether microbiome community shifts mediate the plant tolerance or susceptibility outcomes observed under co-stress. The work develops an original theoretical framework modelling rhizosphere microbiome as a buffer or amplifier of disease outcomes under combined biotic stress. Field validation across three seasons confirms laboratory findings under natural co-stress conditions. Original contributions include the first characterisation of Striga-Fusarium co-stress effects on rhizosphere microbiome composition in West Africa and a novel mechanistic model of microbiome-mediated disease modulation. Keywords: Striga, Fusarium, rhizosphere microbiome, co-stress, savanna Nigeria.