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Front. Microbiol. | doi: 10.3389/fmicb.2018.00277

Indigenous Pseudomonas spp. strains from the olive (Olea europaea L.) rhizosphere as effective biocontrol agents against Verticillium dahliae: from the host roots to the bacterial genomes

  • 1Institute for Sustainable Agriculture, Consejo Superior de Investigaciones Científicas (CSIC), Spain
  • 2Sistemas Genómicos, Spain
  • 3Bioiliberis Research and Development (Spain), Spain

The use of biological control agents (BCA), alone or in combination with other management measures, has gained attention over the past decades, driven by the need to seek for sustainable and eco-friendly alternatives to confront plant pathogens. The rhizosphere of olive (Olea europaea L.) plants is a source of bacteria with potential as biocontrol tools against Verticillium wilt of olive (VWO) caused by Verticillium dahliae Kleb. A collection of bacterial isolates from healthy nursery-produced olive (cultivar Picual, susceptible to VWO) plants was generated based on morphological, biochemical and metabolic characteristics, chemical sensitivities, and on their in vitro antagonistic activity against several olive pathogens. Three strains (PIC25, PIC105 and PICF141) showing high in vitro inhibition ability of pathogens’ growth, particularly against V. dahliae, were eventually selected. Their effectiveness against VWO caused by the defoliating pathotype of V. dahliae was also demonstrated, strain PICF141 being the rhizobacteria showing the best performance as BCA. Genotypic and phenotypic traits traditionally associated with plant growth promotion and/or biocontrol abilities were evaluated as well (e.g. phytase, xylanase, catalase, cellulase, chitinase, glucanase activities, and siderophore and HCN production). Multi-locus sequence analyses of conserved genes enabled the identification of these strains as Pseudomonas spp. Strain PICF141 was affiliated to the ‘Pseudomonas mandelii subgroup’, within the ‘Pseudomonas fluorescens group’, Pseudomonas lini being the closest species. Strains PIC25 and PIC105 were affiliated to the ‘Pseudomonas aeruginosa group’, Pseudomonas indica being the closest relative. Moreover, we identified P. indica (PIC105) for the first time as a BCA. Genome sequencing and in silico analyses allowed the identification of traits commonly associated with plant-bacteria interactions. Finally, the root colonization ability of these olive rhizobacteria was assessed, providing valuable information for the future development of formulations based on these strains. A set of actions, from rhizosphere isolation to genome analysis, is proposed and discussed for selecting indigenous rhizobacteria as effective BCAs.

Keywords: Olea europaea, verticillium wilt, biocontrol, Pseudomonas, rhizobacteria, Pseudomonas indica

Received: 24 Jul 2017; Accepted: 07 Feb 2018.

Edited by:

Brigitte Mauch-Mani, University of Neuchâtel, Switzerland

Reviewed by:

Sotiris Tjamos, Agricultural University of Athens, Greece
JUAN MORAL, Kearney Agricultural Research and Extension Center, University of California, United States  

Copyright: © 2018 Gómez-Lama Cabanás, Legarda Cristobal, Ruano-Rosa, Pizarro-Tobías, Valverde-Corredor, Niqui Arroyo, Trivino, Roca Hernández and Mercado-Blanco. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Dr. Jesús Mercado-Blanco, Consejo Superior de Investigaciones Científicas (CSIC), Institute for Sustainable Agriculture, Madrid, Spain, jesus.mercado@ias.csic.es