Biology and pathogenicity of Xylella fastidiosa associated to olive quick decline syndrome

A large program of mechanical inoculations and vector-mediated transmission experiments
was launched in the past 2 years, and continuously implemented, in the attempt to disclose the role of
the olive-infecting strain of X. fastidiosa in the olive quick decline disease (OQDS) and to ascertain the
crop species under threat due to the expansion of the severe epidemic in southern Italy. Artificial
inoculations were performed using the selected olive strain “De Donno” on different olive and grape
cvs, stone fruit and citrus species, and ornamentals. These plant species, but including a larger
number of olive cultivars, were also tested through field experiments set in the demarcated infected
area, by exposing Xylella-free plants to the natural inoculum pressure and/or by caging naturally
infected Philaenus spumarius. Comparison of the bacterial infection rates recovered upon mechanical
inoculations and vector transmission (field experiments), showed perfect agreement regarding the
susceptibility of the different host species: (i) high rates of systemically infected plants were obtained
for olives, with some differences in relation to the cultivars, oleanders and Poligala myrtifolia; (ii) very
low host colonization occurred for cherry and almond plants; (iii) no bacterial movement and host
colonization could be detected in grapes, citrus, apricot, peach and plum. The pathogenicity of this
strain has been also demonstrated; severe symptoms were detected on the most susceptible hosts.
Acknowledgment
This work was supported by the European Food Safety Authority (EFSA) in the framework of the “Pilot
project on X. fastidiosa to reduce risk assessment uncertainties” (NP.EFSA.ALPHA.2014.07) and by
the European Union’s Horizon 2020 Research and Innovation Programme, under grant agreement
No. 635646, POnTE (Pest Organisms Threatening Europe).