Abstract
In autumn 2013, the presence of Xylella fastidiosa, a xylem-limited Gram-negative bacterium, was detected in olive stands of an area of the Ionian coast of the Salento peninsula (Apulia, southern Italy), that were severely affected by a disease denoted olive quick decline syndrome (OQDS). Studies were carried out for determining the involvement of this bacterium in the genesis of OQDS and of the leaf scorching shown by a number of naturally infected plants other than olive. Isolation in axenic culture was attempted and assays were carried out for determining its pathogenicity to olive, oleander and myrtle-leaf milkwort. The bacterium was readily detected by quantitative polymerase chain reaction (qPCR) in all diseased olive trees sampled in different and geographically separated infection foci, and culturing of 51 isolates, each from a distinct OQDS focus, was accomplished. Needle-inoculation experiments under different environmental conditions proved that the Salentinian isolate De Donno belonging to the subspecies pauca is able to multiply and systemically invade artificially inoculated hosts, reproducing symptoms observed in the field. Bacterial colonization occurred in prick-inoculated olives of all tested cultivars. However, the severity of and timing of symptoms appearance differed with the cultivar, confirming their differential reaction.
Highlights
Olive quick decline syndrome (OQDS) is a disease emerged at the end of the first decade of the XX century in a restricted area of the Ionian coast of Salento (Apulia, southeastern Italy); but the disease incidence increased rapidly through the heavily olive-grown countryside of the peninsula[1]
X. fastidiosa was detected by quantitative polymerase chain reaction (qPCR) in all fifty-eight symptomatic trees sampled in the oldest (2013) and the more recent (2016) olive quick decline syndrome (OQDS) outbreaks
All cultured isolates were confirmed as X. fastidiosa by qPCR and were triple cloned prior to being stored in glycerol at −80 °C
Summary
Olive quick decline syndrome (OQDS) is a disease emerged at the end of the first decade of the XX century in a restricted area of the Ionian coast of Salento (Apulia, southeastern Italy); but the disease incidence increased rapidly through the heavily olive-grown countryside of the peninsula[1]. Isolates recovered from some of these symptomatic trees were successful inoculated and vector-transmitted to olive plants of different cultivars, but under experimental conditions infections did not cause symptoms resembling those observed in the field It was only after the discovery of X. fastidiosa in southern Italian olives, that more in-depth investigations were www.nature.com/scientificreports/. A recent study by Strona et al.[9] underlined that the wide distribution of olive orchards in Apulia and the abundance of a bacterial vector (Philaenus spumarius L.) populations[10] are the factors that contribute the most to the entrenchment of X. fastidiosa in the territory and to the emergence of the associated disease This alarming scenario is further aggravated by the favourable conditions for bacterial growth and host colonization occurring in the coastal areas of the Mediterranean, which are characterized by a temperate climate with mild winters[11,12]
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