CONICET | Buscador de Institutos y Recursos Humanos

The plant growth promoting bacteria (PGPB) are a group of different genera capable of increasing plant growth and productivity. They can operate via various mechanisms such as biological nitrogen fixation, solubilizing phosphates, producing hormones and siderophores, among others, affecting directly the plant metabolism, enhancing root development, altering the enzymatic activities of the plants, or helping to other beneficial microorganisms. The PGPB may also be capable of biological control, promoting plant growth by inhibiting or suppressing plant pathogens. Most of the PGPB used as inoculants have been isolated from the rhizosphere of different plant species. The aim of this study was to evaluate the growth promoting effect in strawberry plants caused by non-rhizosphere soil isolated bacteria, corresponding to the genera Azospirillum, Microbacterium, Paenibacillus and Burkholderia. The trial consisted of bacterial inoculation of strawberry plants in pots containing sterile substrate composed by compost, vermiculite, peat, and perlome (2:1:1:1). Treatments included inoculation with strains irrigation (about 106 cfu/ml) in individual and combined manner, and an uninoculated control. Ten plants per treatment were assessed in a factorial design. Data were subjected to ANOVA and test of statistical significance. The assay was evaluated at 30 days after inoculation and the parameters assessed were: total dry biomass (sum of the organs¡¯ dry weight); growth index (final biomass ¨C initial biomass/initial biomass), root length; crown diameter; number of stolons and leaves; percentage loss of plants and diazotrophs count. Diazotrophs count was performed by the method of the most probable number (MPN) from decimal dilutions roots washed with sterile water and macerated in potassium phosphate buffer 1 M (pH 6.8), in Nfb semisolid medium without nitrogen. The MPN was determined with Mc Crady table for three replicates. Total dry biomass and the growth index was higher in all inoculated treatments, with significant differences on the control (p¡Ü0.05). Among them, Burkholderia, Paenibacillus and Azospirillum showed the highest average values. The root length and the number of stolons and leaves of the bacterial treatments were greater than the control. Crown diameter showed no significant differences between treatments and the control. Besides, 40% loss in the control plants, compared with the inoculated treatments was also observed. The diazotrohs count was higher in all inoculated treatments on the control being Burkholderia with the higher value. Bacteria isolated from nonrhizosphere soil, but with plant growth-promoting characteristics were able to associate with strawberry plants and promote their growth.