Characterization of the antifungal and plant growth-promoting effects of diffusible and volatile organic compounds produced by Pseudomonas fluorescens strains

Abstract

We analyzed the antifungal and plant growth-promoting (PGP) effects of diffusible and volatile organic compounds (VOCs) produced by new rhizospheric isolates. The bacterial strains were identified as Pseudomonas fluorescens UM16, UM240, UM256, and UM270, based on their complete 16S ribosomal gene sequencing. These pseudomonads showed a high degree of antagonism against the phytopathogen Botrytis cinerea during confrontation assays. In addition, all strains significantly increased Medicago truncatula biomass and chlorophyll content. Interestingly, these activities were exerted by the emission of either diffusible organic compounds or VOCs. During biocontrol experiments, the four P. fluorescens strains were able to protect M. truncatula plants from B. cinerea infection by reducing stem disease symptoms and root browning. The potential presence of phenazines, cyanogens, and ACC (1-aminocyclopropane-1-carboxylate) deaminase, as well as the production of biofilm, siderophores, proteases, and indole-3-acetic acid were identified in most of the strains. The VOCs emitted by all four Pseudomonas strains were similar, and sulfur-containing compounds were among the most abundant, including dimethyl disulfide. Interestingly, the strain UM270 was the only one that produced dimethylhexadecylamine, a compound with antifungal and PGP activities. In conclusion, the Pseudomonas strains analyzed here exert multiple antagonistic and PGP mechanisms, and represent an excellent option to be used as either biocontrol or biopromoting agents in crops.