The potential of indigenous bacteria from the olive rhizosphere as biological control agents against a broad range of phytopathogens

Abstract: Verticillium wilt (Verticillium dahliae Kleb.) is one of the main biotic constraints affecting olive cultivation in the Mediterranean Basin. The difficulty to control this disease has urged researchers to seek effective measures within an integrated management framework. Biological control, alone or combined with other approaches, emerges as one of the most promising alternatives to confront this pathogen. In this study, a collection of indigenous culturable bacteria (> 300) from olive roots was generated. First selection was performed based on their antagonistic activity against V. dahliae. As a result, 189 isolates were selected which were: (i) tested against a battery of relevant olive pathogens (V. dahliae, Pseudomonas savastanoi pv. savastanoi, Rosellinia necatrix, Colletotrichum godetiae and Colletotrichum nymphaeae); (ii) identified molecularly; and (iii) screened for the presence of phenotypes usually associated to antagonism and/or plant growth promotion (PGP). Results showed predominance of phyla Proteobacteria and Firmicutes, Pseudomonas and Bacillus being the most abundant genera. Although none of the strains showed effective against all tested pathogens, many of them displayed a broad antagonistic activity, particularly strains of the genus Paenibacillus. Phenotypic characterization revealed enzymatic activities usually associated to biocontrol and PGP, such as production of catalase and siderophores, among others. This fact together with the observed broad antagonist activity allow us to conclude that some of these bacteria are good candidates to be used as biological control agents in future bioformulations against diverse relevant olive pathogens.