Host Plants, Not Soils, Shape the Phylogenetic Assembly of Culturable Legume-Associated Bacteria

Understanding how environmental and host factors shape plant microbiomes is essential for predicting plant–microbe interactions. We investigated the influence of soil origin and legume host identity on bacterial communities associated with cowpea ( Vigna unguiculata ), groundnut ( Arachis hypogaea ), and mungbean ( Vigna radiata ) grown in five contrasting soils. Seventy-seven bacterial isolates were characterised by 16S rRNA gene sequencing and Maximum Likelihood phylogenetic analysis. Diversity was assessed using richness, Shannon diversity, rarefaction analyses, Bray–Curtis-based PCoA, and unweighted UniFrac distances. Soil-derived communities showed broad phylogenetic dispersion and high variability in composition and richness, reflecting their role as reservoirs of microbial diversity. In contrast, plant-associated communities displayed host-specific clustering and lower variability. Groundnut-associated communities were more distinct than those of cowpea and mungbean. Soil defines the available bacterial pool, while legumes selectively recruit and structure subsets of this diversity, highlighting host-driven filtering in microbiome assembly.