| Summary: | The production of volatile organic compounds (VOCs) represents a promising strategy of plant-beneficial bacteria to control soil-borne phytopathogens. <i>Pseudomonas</i> sp. PICF6 and <i>Pseudomonas simiae</i> PICF7 are two indigenous inhabitants of olive roots displaying effective biological control against <i>Verticillium dahliae.</i> Additionally, strain PICF7 is able to promote the growth of barley and <i>Arabidopsis thaliana</i>, VOCs being involved in the growth of the latter species. In this study, the antagonistic capacity of these endophytic bacteria against relevant phytopathogens (<i>Verticillium</i> spp., <i>Rhizoctonia solani</i>, <i>Sclerotinia sclerotiorum</i> and <i>Fusarium oxysporum</i> f.sp. <i>lycopersici</i>) was assessed. Under in vitro conditions, PICF6 and PICF7 were only able to antagonize representative isolates of <i>V. dahliae</i> and <i>V. longisporum</i>. Remarkably, both strains produced an impressive portfolio of up to twenty VOCs, that included compounds with reported antifungal (e.g., 1-undecene, (methyldisulfanyl) methane and 1-decene) or plant growth promoting (e.g., tridecane, 1-decene) activities. Moreover, their volatilomes differed strongly in the absence and presence of <i>V. dahliae</i>. For example, when co incubated with the defoliating pathotype of <i>V. dahliae,</i> the antifungal compound 4-methyl-2,6-bis(2-methyl-2-propanyl)phenol was produced. Results suggest that volatiles emitted by these endophytes may differ in their modes of action, and that potential benefits for the host needs further investigation <i>in planta</i>.
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