**5. Conclusions**

Our results indicate that the influence of biological treatments against the pathogen depends on the genotype, since the greater the resistance of the cultivar, the lower the influence of the treatments on the ability of OSE to inhibit conidia germination. In 'Picual', the most susceptible cultivar to VWO, the BCA *B. amyloliquefaciens* PAB-024 and a phosphonate salt [copper phosphite (Phoscuprico®)] were the most effective treatments in inhibiting conidia germination by OSE. Thus, the results suggest that the high tolerance to *V. dahliae* conferred by the 'Frantoio' genotype prevails over the treatments, even those that were more effective against the pathogen in susceptible cultivars. The method used in this study to obtain endosphere contents of olive plants, called OSE or 'sap-like' for further analysis in the laboratory against *V. dahliae* can be considered valid and useful since all our results agree with those obtained in previous studies. Thus, this work represents a first approach to elucidate the role of cultivar and biological treatments in modifying the effect on the pathogen of the endosphere content of olive plants.

**Author Contributions:** Laboratory tasks, data analyses, writing and editing: A.L.-M.; data analyses, writing, review, and editing: C.A.-B.; laboratory tasks: F.M.L.-E.; study conception and design, funding acquisition, supervision, and manuscript revision: A.T. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the Spanish Ministry of Science, Innovation and Universities (MICINN; projects GIVEROLI Ref. AGL2016-76240-R and VERTOLEA Ref. AGL2016-76240-R), cofinanced by the European Union FEDER Funds. A. López-Moral is holder of "Formación de Personal Investigador" fellowship (FPI; contract number BES-2017-081839) from MICINN. We acknowledge financial support of MICINN, the Spanish State Research Agency, through the Severo Ochoa and María de Maeztu Program for Centres and Units of Excellence in R&D (Ref. CEX2019-000968-M).

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Acknowledgments:** The authors thank F. González and J.A. Toro for their skilful technical assistance. The authors also thanks AGRI nova Science (Almería, Spain), Daymsa S.A. (Zaragoza, Spain), and IDAI Nature (Valencia, Spain) for their kind collaboration providing experimental samples of Phoscuprico®, Naturfos®, and IDAI Brotaverd®, respectively, to conduct this study.

**Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.
