Olive quick decline and Xylella fastidiosa in Southern Italy: the state of the art

The identification in 2013 of an outbreak of Xylella fastidiosa (Xf) in olive groves in the Salento peninsula
(southern Italy) resulted in a plant health emergency of unprecedented proportions for the EU. Infected
olive trees show extensive desiccation of the canopy and severe quick decline symptoms. In the outbreak
area, the bacterium was found to be efficiently spread by the meadow spittlebug Philaenus spumarius,
abundant on the olive canopies during the dry season. The initial demarcated foci rapidly expanded over
the past 4 years, establishing a new demarcation line distant 80 km from the first reported outbreak;
while few species were found infected in 2013 the currently known susceptible hosts reached the number
of ca. 30 different plant species. Phytosanitary measures to combat the spread and mitigate the impact
of the bacterial infections, included restrictions for the new plantations, for the movement of propagating
materials and removal of infected trees. The severe damage suffered by the infected olive trees combined
with the imposed phytosanitary restrictions determined severe economic and social impacts in the local
community, raising major concerns against the application of the containment measures and determining
the failure to implement timely, effective and coordinated preventive measures. Due to the novelty of
the Xylella‐associated disease in olives and in general the fact that Xf is conquering new geographical
area, like the EU territories, the EU Commission mobilized dedicated resources to build EU research
actions to fulfil research gaps for this emerging pathogen threatening the entire EU territory. Between
2015 and 2016, two relevant research projects in the framework of the H2020 programs have been
funded: the project "Pest Organisms Threatening Europe" (POnTE) and the project "Xylella Fastidiosa
Active Containment Through a multidisciplinary‐Oriented Research Strategy" (XF‐ACTORS) the latter
targeting exclusively Xf. From the intense research activity developed in the past three years some major
results have been already achieved, providing data on the genetic and biological properties of the
population of the bacterium, the range of hosts, the identification and biology of the vector, the
identification of olive cultivars with promising traits of resistance.