Quantification of the potential biocontrol and direct plant growth promotion abilities based on multiple biological traits distinguish different groups of Pseudomonas spp. isolates

Members of the Pseudomonas genus colonize the rhizosphere of different plant species and display plant-probiotic traits. Therefore, they are interesting candidates for biological agricultural inputs to stimulate plant development and/or promote crop health. We have generated a collection of 19 isolates of pseudomonads obtained from either bulk soil or the rhizosphere of healthy individuals of major extensive crops from different plots under no-till management located in Argentina. Isolates were selected for their ability to antagonize several fungal pathogens recovered from infected soybean and maize plants. Partial sequencing of 16S rDNA, oprF and rpoB genes positioned isolates within all major pseudomonads groups. Most isolates colonized the rhizosphere of soybean and maize seedlings without affecting germination or development. Members of the Pseudomonas chlororaphis subgroup, and one isolate of the Pseudomonas putida subgroup, displayed the widest antifungal spectrum and strongest antagonistic potential. A principal component analysis based on the outcome of quantitative and qualitative tests related to biocontrol of fungal pathogens, direct plant growth promotion, and other root colonization-related traits, showed that isolates with the highest antagonistic potential and mostly of soil origin were grouped together, whereas rhizospheric isolates and those with strong flagellar-dependent motility, exoprotease production and biofilm development, were clustered in a separate group. Interestingly, quantitative comparison of newly developed biocontrol and direct growth promotion indices revealed that these two plant probiotic traits are rather associated to different set of isolates, and rarely present in the same pseudomonad strains. These indices could be employed to screen and categorize isolates by their potential to act as a biocontrol or a biofertilizer agent. (C) 2015 Elsevier Inc. All rights reserved.