Authors:
Massimiliano Cardinale1, Andrea Luvisi2*, Joana B. Meyer3, Erika Sabella2, Luigi De Bellis2, Albert C. Cruz4, Yiannis Ampatzidis5 and Paolo Cherubini3
1-Institute of Applied Microbiology, Research Center for BioSystems, Land Use, and Nutrition, Justus-Liebig-University Giessen, Giessen, Germany
2-Department of Biological and Environmental Sciences and Technologies, University of Salento, Lecce, Italy
3-WSL Swiss Federal Research Institute, Birmensdorf, Switzerland
4-Department of Computer and Electrical Engineering and Computer Science, California State University, Bakersfield, CA, United States
5-Department of Agricultural and Biological Engineering, Southwest Florida Research and Education Center, University of Florida, Gainesville, FL, United States
Published online:
6 April 2018
Source:
Frontiers in Plant Science
https://www.frontiersin.org/articles/10.3389/fpls.2018.00431/full
Abstract:
The colonization behavior of the Xylella fastidiosa strain CoDiRO, the causal agent of olive quick decline syndrome (OQDS), within the xylem of Olea europaea L. is still quite controversial. As previous literature suggests, even if xylem vessel occlusions in naturally infected olive plants were observed, cell aggregation in the formation of occlusions had a minimal role. This observation left some open questions about the whole behavior of the CoDiRO strain and its actual role in OQDS pathogenesis. In order to evaluate the extent of bacterial infection in olive trees and the role of bacterial aggregates in vessel occlusions, we tested a specific fluorescence in situ hybridization (FISH) probe (KO 210) for X. fastidiosa and quantified the level of infection and vessel occlusion in both petioles and branches of naturally infected and non-infected olive trees. All symptomatic petioles showed colonization by X. fastidiosa, especially in the larger innermost vessels. In several cases, the vessels appeared completely occluded by a biofilm containing bacterial cells and extracellular matrix and the frequent colonization of adjacent vessels suggested a horizontal movement of the bacteria. Infected symptomatic trees had 21.6 ± 10.7% of petiole vessels colonized by the pathogen, indicating an irregular distribution in olive tree xylem. Thus, our observations point out the primary role of the pathogen in olive vessel occlusions. Furthermore, our findings indicate that the KO 210 FISH probe is suitable for the specific detection of X. fastidiosa.