Abstract
The use of biological control agents (BCAs) is of interest within an integrated management strategy of Verticillium wilt of olive (VWO) caused by the soil-borne fungus Verticillium dahliae Kleb. Previous studies have shown that the root/rhizosphere of healthy olive plants is an important reservoir of microorganisms displaying biocontrol activity against VWO (i.e., Pseudomonas strains PICF7 and PIC141). Moreover, these BCAs are already adapted to the ecological niche where they are deployed. Three novel bacteria (strains PIC28, PIC73 and PIC167) from nursery-produced olive plants were in-depth characterized using a previously implemented approach consisting of in situ isolation, in vitro antagonism tests, in planta bioassays, phenotypic and metabolic characterization, genome analyses and in silico identification of traits involved in plant-bacteria interactions, and multi-locus sequence analyses. All strains displayed in vitro growth inhibition of different olive pathogens and biocontrol effectiveness against Verticillium dahliae, with strain PIC73 being the most effective BCA. Strains PIC73 and PIC167 were identified as Paenibacillus polymyxa (Prazmowski) Ash et al. and Paenibacillus terrae Yoon et al., respectively. Strain PIC28 belongs to the Bacillus genus. Some of these Bacillales members showed in vitro compatibility with previously characterized BCAs (Pseudomonas spp. strains) also originating from the olive rhizosphere, paving the way for the future development of tailored bacterial consortia effective against VWO.
Highlights
Verticillium wilt of olive (VWO) is one of the most serious diseases affecting olive (Olea europaea L.subsp. europaea var. europaea) cultivation worldwide
This study focused on three Gram-positive strains of an olive rhizobacteria collection obtained from roots of one-year-old ‘Picual’ plants, a cultivar qualified as highly susceptible to V. dahliae [26], collected from ten commercial nurseries located in Córdoba province (South Spain)
Strain PIC73 could be unambiguously identified as Paenibacillus polymyxa (Prazmowski) Ash et al (99% identity, e-value 0.0), and strain PIC167 as Paenibacillus terrae Yoon et al (96% identity, e-value 0.0)
Summary
Verticillium wilt of olive (VWO) is one of the most serious diseases affecting olive (Olea europaea L.subsp. europaea var. europaea) cultivation worldwide. Verticillium wilt of olive (VWO) is one of the most serious diseases affecting olive Verticillium dahliae Kleb., the causal agent of VWO, is responsible for substantial production losses thereby constituting the main phytopathological issue in many olive-growing regions. All these factors make it difficult for an efficient control of VWO, and available measures have so far proven unsuccessful when implemented individually. An integrated disease management strategy is recommended, highlighting pre-plating control tools since no resistant varieties and/or effective fungicides are available. Within this context, the development and use of biological control agents (BCAs) is an appealing, sustainable and environmentally friendly management approach to control VWO
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