Functional Characterisation of Resistance Gene Analogues in Vigna unguiculata for Broad-Spectrum Disease Resistance Against Viral and Fungal Pathogens in Nigeria

Cowpea (Vigna unguiculata) is a nutritionally critical and economically important legume crop in Nigeria, threatened by multiple pathogens including Cowpea Mosaic Virus, Bean Common Mosaic Virus, Cowpea Aphid-Borne Mosaic Virus, and Colletotrichum truncatum. The genetic basis of resistance in cowpea, particularly the functional role of resistance gene analogue candidates identified from the cowpea reference genome, remains incompletely characterised, limiting the precision of resistance breeding programmes. This doctoral research functionally characterises a selected panel of 12 nucleotide-binding leucine-rich repeat resistance gene analogues in cowpea with predicted recognition specificity against protein effectors from the major Nigerian viral and fungal cowpea pathogens. The research employs virus-induced gene silencing to silence each candidate resistance gene analogue in susceptible and resistant cowpea backgrounds, followed by challenge inoculation with four Nigerian pathogen isolates representing the major pathosystem stressors. RNA-seq transcriptome analysis compares silenced versus non-silenced resistant plants following each pathogen challenge to identify downstream defence networks activated through each resistance gene analogue. Protein-protein interaction assays using yeast-two-hybrid and split-GFP systems test direct interactions between cowpea resistance gene analogue products and pathogen effectors. The dissertation delivers the first functional characterisation of cowpea resistance gene analogues against multiple pathogen classes in West Africa, an original mechanistic model of resistance gene analogue-mediated broad-spectrum defence in cowpea, and a prioritised list of resistance gene analogues for inclusion in molecular breeding programmes. Keywords: cowpea, resistance gene analogues, broad-spectrum resistance, functional characterisation, Nigeria.