Rescue and genetic assessment of soybean-nodulating Bradyrhizobium strains from an experimental field thirty years after inoculation

As the long-term phenotype and genetic stability of bacteria used as inoculant are important parameters in their ecology and for agricultural purposes, this study aimed genotypically characterize several-rescued bradyrhizobia of an experimental field thirty years after the first inoculation. A high genetic diversity of 30 bradyrhizobia isolates was observed, either by AFLP (H = 4.87) or rep-PCR (H = 4.18). The results indicate that the Bradyrhizobium population that persists in the Eldorado soil is genetically very diverse and different from the parental strains. All isolates were infective and trapped in IAS-5 soybean variety maintaining their nodulation and nitrogen fixation properties. Given that many rhizobia in a soil can lost the infective capacity and that the host genotype can affect the spectrum of rhizobial genotype selected from a soil, the genetic diversity of the complete bradyrhizobia population in Eldorado soil could be even higher than the identified in this work.