Published October 29, 2019 | Version v1
Conference paper Open

Evaluation of vascular occlusions in xylem vessels of olive cultivars infected with Xylella fastidiosa

  • 1. Dipartimento di Scienze del Suolo, della Pianta e degli Alimenti, Università degli Studi di Bari Aldo Moro
  • 2. Dipartimento di Scienze del Suolo, della Pianta e degli Alimenti, Università degli Studi di Bari Aldo Moro; Centro di ricerca, Sperimentazione e formazione in agricoltura "Basile Caramia ", Locorotondo (IT)

Description

Understanding the mechanisms of the development of symptoms of
Olive Quick Decline Syndrome (OQDS) and the different olive cultivar responses to
infections caused by Xylella fastidiosa subsp. pauca, ST53, is fundamental for disease
control. The combined action of bacterial aggregates and plant-derived vascular occlusions
(tyloses, gums and gels) has been invoked as the cause of the pathogenic alterations
occurring in Xylella-infected plants. Conflicting observations were found about the role of
vascular occlusion in the disease progression in field-grown olives. In the present work the
distribution of vascular occlusions in the secondary xylem vessels of susceptible, Cellina di
Nardò, and resistant, Leccino and FS17, cultivars were studied by light microscope
observations of toluidine blue stained sections, recovered from stems of greenhouse-grown
mock and artificially inoculated olives. One-year-old shoot portions collected from
symptomatic or symptomless twigs were first tested by qPCR and used to recover thin
sections (0.2 mm thick), with a similar number of vessels inspected for each cultivar. In
the sections recovered from the non-infected controls 0.15%, 0.02% and 0.13% of
occluded vessels were present, respectively in Cellina, Leccino and FS17. These
percentages increased in the infected twigs reaching 9.65%, 6.81% and 1.33% in Cellina,
Leccino and FS17, respectively, indicating that Xylella infections (regardless of the
cultivar) induced occlusions of the xylem vessels; these were significantly higher in the
susceptible cultivar. More specifically, percentages of occluded vessels in the susceptible
ranged cultivar from 1% to 34%, while those of the resistant Leccino and FS17 ranged
from 0.044% to 14% and 1.09% to 1.53%, respectively. Although a clear-cut difference
was observed among the infected cultivars, no significant differences within each cultivar
were recorded between symptomatic and non-symptomatic shoots, suggesting that the
development of symptoms is a combination of different factors (anatomical,
chemical and physical).

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Additional details

Funding

POnTE – Pest Organisms Threatening Europe 635646
European Commission
XF-ACTORS – Xylella Fastidiosa Active Containment Through a multidisciplinary-Oriented Research Strategy 727987
European Commission