An Original Investigation into the Role of Plant Microbiome in Mediating Drought Tolerance in Cowpea Under Nigerian Field Conditions

The plant microbiome, encompassing rhizosphere and endophytic microbial communities, can significantly influence plant drought tolerance through osmolyte production, phytohormone synthesis, and stress signalling modulation, and original investigation of how these microbiome-mediated drought tolerance mechanisms operate in cowpea under Nigerian field soil conditions is a new and important research frontier. This study conducted an original investigation into plant microbiome-mediated drought tolerance in cowpea under field conditions in Kano and Katsina States, North West Nigeria. A multi-season field experiment was designed to compare drought-tolerant and susceptible cowpea lines under rain-fed (stress) and supplementally irrigated (non-stress) conditions, with simultaneous characterisation of rhizosphere and root endosphere microbial communities by amplicon 16S rRNA and ITS2 sequencing. A total of 24 plots across six cowpea genotypes and two water treatments were sampled at flowering and at pod fill. Alpha and beta diversity, indicator taxa analysis, and structural equation modelling linking microbiome composition to plant drought tolerance physiology were applied. Results showed significantly higher bacterial diversity in drought-tolerant versus susceptible genotype rhizospheres under stress conditions. Actinobacteria and Bacillus species were enriched in drought-tolerant genotype rhizospheres. Structural equation modelling confirmed that microbiome composition mediated 27 percent of the drought tolerance phenotype independent of host genetics. Three novel Bacillus and Arthrobacter strains isolated from tolerant genotype roots produced ACC deaminase and abscisic acid analogues in culture. The study represents an original contribution to microbiome-drought tolerance interaction science in cowpea.

Keywords: plant microbiome, drought tolerance, cowpea, rhizosphere, Nigeria