Characterization and interactions between rice-associated bacteria with plant-growth promoting properties

Abstract

Rice (Oryza sativa) is one of the main cereals exported by Uruguay. Nowadays it is imperative to improve the performance of the cropping system to increase the yields. The PGPB (Plant Growth Promoting Bacteria) are an option to raise the yields and to reach sustainable production by reducing the agrochemicals input. The goal of this work was to isolate and characterize rice-associated bacteria able to fix atmospheric nitrogen or solubilize inorganic phosphate, and to study their performance in vitro facing to other PGPB. Soils from different regions and properties were employed to grow rice from seeds, under controlled conditions. Ninety isolates of endophytic and rizospheric bacteria were obtained. Diazotrophic activity was assessed by ARA (Acetylene Reduction Assay) and nifH gene amplification. The diversity of the isolates was screened by ARDRA (Amplified Ribosomal DNA Restriction Analysis) and the identification was performed by partial sequencing of the 16S rRNA gene. The endophytic diazotrophic bacteria were unable to solubilize phosphate and belong to the genera Azospirillum, Herbaspirillum, Enterobacter, Paenibacillus and Pleomorphomonas. All the rizospheric phosphate-solubilizing isolates are diazotrophs and affiliated to the genus Burkholderia. Most of the characterized isolates produce siderophores and indolacetic acid. Some strains of Burkholderia were antagonists in vitro of PGPB of the genera Azospirillum and Herbaspirillum that are employed as inoculants in grasses. These results show that the native beneficial bacteria associated to the plant from different soils may influence the success of the inoculation with PGPB.