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 further check that transient decrease of Psv population and modification of tumour's macroscopic appearance were due to the presence of strain PICF7, epifluorescence microscopy combined with fluorescent tagging of Psv NCPPB 3335 with GFP (Psv-GFP) was used. In agreement with results from previous bioassays, a decrease of Psv NCPPB 3335 population in tumours developed in plants co-inoculated with the BCA was visualized during the first 14 days. Lower population of the pathogen was revealed as a depletion of the green fluorescence at the inoculation points and within the hyperplasic tissue developed in Psv/PICF7 co-inoculated plants (Fig. 3A, 2–13 DAI), compared with those ones only inoculated with Psv alone (Fig. 3B, 2–13 DAI). As in previous bioassays, NCPPB 3335 population in Psv/PICF7 co-inoculated plants recovered over time, and tumours from both treatments reached similar levels of fluorescence (Fig. 3A, 27 DAI and B, 27 DAI). Population size of Psv recovered from knots along the experiment confirmed that the observed fluorescence fluctuation correlated to a decrease in Psv colony counts (approximately 1.5 order of magnitude lower) at all times except at 27 DAI (6.8 ± 0.3, for Psv alone and 6.5 ± 0.1, for Psv/PICF7 coinoculated plants), as shown in previous bioassays (see above). Finally, macroscopic appearance of tumours developed in this assay differed depending on the presence or not of the BCA (Fig. 2C and D), confirming previous observations.
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.