Selection of Soybean Root Nodule Endophytes: Competition Between Bradyrhizobium and Sinorhizobium Strains Inoculated at Different Plant Growth Stages

Soybean is frequently nodulated by species from the Bradyrhizobium (BR) and/or Sinorhizobium (SR) genera. Several factors, such as soil pH, host genotype, geographic location, and other environmental variables, are reported to influence the preferential selection between BR or SR species within soybean root nodules. However, it remains unclear whether the age of the host plant at the time of inoculation affects preferential strain selection. We inoculated soybean plants with different cell densities of BR and SR strains at three time points: at sowing (T0), two weeks after germination (T2), and four weeks after germination (T4), to investigate the potential role of host plant age in driving selection between two compatible strains. We used 16S rRNA gene amplicon sequencing of root nodule and rhizosphere samples to assess the relative nodule occupancy and rhizosphere establishment of BR and SR.