From the root to the stem: interaction between the biocontrol root endophyte Pseudomonas fluorescens PICF7 and the pathogen Pseudomonas savastanoi NCPPB 3335 in olive knots.
Bottom Line: While PICF7 was not able to suppress disease development, its presence transiently decreased pathogen population size, produced less necrotic tumours, and sharply altered the localization of the pathogen in the hyperplasic tissue, which may pose epidemiological consequences.However, presence of the BCA seemed to confine P. savastanoi at inner regions of the tumours.This approach has also enabled to prove that the pathogen can moved systemically beyond the hypertrophied tissue.
Affiliation: Departamento de Protección de Cultivos, Instituto de Agricultura Sostenible, Consejo Superior de Investigaciones Científicas-CSIC, Alameda del Obispo s/n, Apartado 4084, E-14080 Córdoba, Spain.Show MeSH
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Mentions: To assess whether differences observed in the external, macroscopic anatomy between tumours developed in Psv-inoculated and Psv/PICF7 co-inoculated plants could correlate to changes in pathogen distribution mediated by PICF7 presence, fluorescent tagging of bacteria (Psv-GFP and PICF7-RFP), vibratome-sectioning of knot and stem tissues and CLSM were used. By combining these microscopy and biotechnological tools we aimed to explore the inner anatomy of tumours as well as the localization and distribution of the BCA and the pathogen on and within knots in vivo, without implementing further tissue manipulation, fixation and/or staining procedures. Overall, sectioning of knots from plants co-inoculated with Psv and PICF7 was more difficult, as they presented spongy consistency compared with tumours generated by single inoculation of Psv. CLSM images showed that, in co-inoculated plants, both bacteria could be found mixed within vascular vessels of the stem at early stages of the knot development (7 DAI, Fig. 4A and B). However, from 2 weeks after artificial inoculation of bacteria until the end of the experiments (6–9 weeks), each bacterial species tended to be allocated in different regions of the tumours in most of the observations (Fig. 4C). Indeed, while both fluorescently tagged Pseudomonas could be found mixed at any place within the knot, particularly at the beginning of the knot development (Fig. 4A and B), PICF7-RFP cells were predominantly visualized at the knot surface or in outer regions of the tumour (Fig. 4C and D). In contrast, Psv-GFP cells were mainly found at the inner regions of the hyperplasic tissue, particularly at later times of the experiment (Fig. 4C; Fig. 5B, D and F). Remarkably, localization of Psv colonies greatly differed depending on the presence of strain PICF7. Results showed that when strain NCPPB 3335 was inoculated alone the pathogen predominantly colonized the surface of the tumour (Fig. 5A, C and E).
Affiliation: Departamento de Protección de Cultivos, Instituto de Agricultura Sostenible, Consejo Superior de Investigaciones Científicas-CSIC, Alameda del Obispo s/n, Apartado 4084, E-14080 Córdoba, Spain.