Genetic Variability of Rhizobium and its Correspondence with Plant Genotype Response: A Systematic Review

Rhizobium-legume symbiosis is a cornerstone of sustainable agriculture, yet the integrated understanding of how bacterial genomic variation determines phenotypic outcomes across different host genotypes remains fragmented. This systematic review aims to synthesize the correspondence between Rhizobium genetic variability and plant genotype responses. Using a structured PRISMA framework, 86 studies were selected to analyze genomic diversity patterns, host responsiveness, and Genotype × Genotype (G×G) interactions. The synthesis reveals that rhizobial diversity is shaped by variations in housekeeping genes, symbiotic islands, and plasmid-borne nod and nif clusters, which drive nodulation competitiveness and environmental adaptation. Correspondingly, host plant responsiveness is actively modulated by specific genetic architectures, such as Rj genes in soybeans and immune receptors in Medicago, creating a selective filter for bacterial partners. The results demonstrate consistent G×G specificity, ranging from strict compatibility in specialized systems to flexible interactions in woody legumes, all of which are influenced by environmental pressures. A conceptual framework is proposed, describing symbiosis as an emergent system where microbial genomic modules interact with plant regulatory networks to determine nitrogen fixation efficiency. The study concludes that optimizing agronomic performance requires coordinating microbial genomic traits with host plant genetics, emphasizing the need for genotype-matched inoculants and molecular breeding strategies to enhance biological nitrogen fixation stability.