Bacterial Assembly in the Switchgrass Rhizosphere Is Shaped by Phylogeny, Host Genotype, and Growing Site

If microbial traits are phylogenetically conserved, then variation in traits of plant hosts may influence rhizosphere microbiomes at higher taxonomic levels. To test this hypothesis and genotype-by-environment-by-microbiome (G × E × M) interactions in switchgrass (Panicum virgatum), we assessed rhizosphere bacterial composition using 128 host genotypes grown at three distinct field sites. First, we found that growing site was a substantial driver of bacterial composition and that specific bacterial taxa correlated with differences in disease incidence and yield across environments. Second, broad-sense heritability analyses revealed that host genetic effects on rhizosphere composition were strongest at the genus level, suggesting a conserved genetic basis for shaping beneficial or pathogenic taxa. Third, we identified shared host genetic variants associated with bacterial abundance and plant metabolism, indicating possible linkages between key microbial traits and agronomic performance. These findings underscore the importance of incorporating rhizosphere microbiomes into switchgrass breeding efforts and call for further investigation of G × E × M interactions to pinpoint microbial interventions that enhance yield and disease resistance.