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

Grapevine leafroll-associated closterovirus 7 in Greece

An extensive survey was carried out to assess, by ELISA, the occurrence of grapevine closteroviruses in several grape-growing areas of Greece, with particular regard to GLRaV-7. Samples were collected in commercial vineyards and varietal collections from apparently symptomless and symptomatic leafroll vines. GLRaV-7 was widely distributed and frequently associated with GLRaV-1 and GLRaV-3. ELISA was suitable for GLRaV-7 detection but the reagents utilized in this study must be improved

Xylella fastidiosa: il patogeno, le malattie e l’attuale situazione fitosanitaria

Xylella fastidiosa è un batterio fitopatogeno Gram negativo che appartiene alla famiglia delle Xanthomonadaceae. È l’agente causale di numerose malattie d’importanti colture arboree, erbacee, forestali e ornamentali e, a differenza di quanto molta parte dell’opinione pubblica crede, non è un problema di recente comparsa, ma ha una lunga storia che affonda le sue radici ancora alla fine del diciannovesimo secolo. L’etimologia e la semantica del nome assegnato al patogeno da parte dei ricercatori che per primi lo isolarono in coltura pura svelano due aspetti fondamentali della sua biologia: Xylella rivela la nicchia biologica del patogeno all’interno delle sue piante ospiti, cioè lo xilema; fastidiosa indica la grande difficoltà che il batteriologo incontra durante il processo d’isolamento e purificazione della coltura pura

First Report of 'Candidatus Phytoplasma phoenicium' on Almond in Southern Italy

In spring 2017, phytoplasma suspected symptoms were reported on 25% of 15-year-old almond plants, cultivars Filippo Ceo and Genco grafted onto GF677, in a commercial orchard (20 ha) located at Grottaglie, Apulia (southeast Italy). Among the symptoms, development of many axillary buds with small and yellowish leaves, and witches' brooms developing from the trunk, were the most frequent, followed by leaf rosetting, proliferation of slender shoots, tree decline, and dieback

Complete Genome Sequence of the Olive-Infecting Strain Xylella fastidiosa subsp. pauca De Donno

We report here the complete and annotated genome sequence of the plant-pathogenic bacterium Xylella fastidiosa subsp. pauca strain De Donno. This strain was recovered from an olive tree severely affected by olive quick decline syndrome (OQDS), a devastating olive disease associated with X. fastidiosa infections in susceptible olive cultivars

First international proficiency testing for laboratory performance on Xylella fastidiosa detection

A proficiency test (PT) to evaluate the performance of laboratories involved in molecular and serological detection of X. fastidiosa was carried out in early 2017; 35 laboratories from EU/non- EU Countries tested 4 different methods to purify DNA, conventional and qPCR assays, and 2 ELISA tests. The number of resultant positive agreement/negative agreement/positive deviation/negative deviation was used to determine the laboratory performance (i.e. accuracy 100%). The overall results showed that all laboratories were able to correctly diagnose X. fastidiosa in the blind samples containing the highest X. fastidiosa concentrations, whereas the performance of several laboratories was negatively affected by the lack of detection in the samples with the lowest concentrations, both through molecular and serological tests. Accuracy level of 100% (laboratory conformed to the PT) was successfully recovered in the majority of the laboratories performing qPCR and PCR assays on DNA purified using at least 2 of the 4 tested protocols. The use of automated platform ensured higher laboratory performance. As expected, results of the ELISA tests generated lower performance values in the majority of the laboratories, due to the lack of detection of positive samples containing the lowest the bacterial concentration. This study provides a good overview on the laboratory performance for the diagnostics currently used in the EPPO countries and indicate useful improvements that laboratories can adopt to achieve a better performance

Survey of Auchenorrhyncha in the Salento peninsula in search of putative vectors of Xylella fastidiosa subsp. pauca CoDiRO strain

Xylella fastidiosa (Xf) was identified in September 2013 in olive trees affected by the Olive quick decline syndrome (OQDS) in the Salento peninsula (southern Italy) and denoted Xf strain CoDiRO. Xf is comprised of a group of genetically diverse bacteria in the class Gammaproteobacteria that causes severe plant diseases in many crops and ornamentals. The bacterium is acquired and transmit- ted by xylem-sap feeding hemipterans such as sharpshooter leaf- hoppers (Cicadellidae, Cicadellinae), froghoppers and spittlebugs (Aphrophoridae and Cercopidae) and, possibly, cicadas (Cicadidae and Tibicinidae). Due to the rapid spread and devastation associ- ated with OQDS, a survey of candidate vectors of Xf was conducted from September 2013 in the Gallipoli area in accordance to a EFSA list (EFSA, 2013). Four candidate vector species were identified: (i) Aphrophoridae: Philaenus spumarius L. and Neophilaenus camp- estris Fallen; (ii) Cercopidae: Cercopis sanguinolenta Scopoli; (iii) Ci- cadidae: Cicada orni L. Among these, only P. spumarius, the meadow spittlebug, was experimentally proven to be a vector of X. fastidiosa strain CoDiRO. A high percentage of meadow spittlebugs collected from OQDS-affected orchards, from May to September 2014, tested positive for X. fastidiosa by PCR. Transmission to periwinkle plants was successful. Laboratory tests, so far limited to the Philaenus-ex- posed periwinkle seedlings, will be extended to the entire panel of the host plants (olives, grapes, citrus, oleander and Prunus spp.) that were exposed to infectious spittlebugs. Further ongoing experiments include Xf-free spittlebugs that were allowed to feed on infected olives and other hosts plants prior to transferring onto receptor host plants. The results so far obtained have shown that olive is a source of inoculum from which P. spumarius is able to acquire the bacte- rium and transfer it to other olives. These data strongly suggest that the main vector of Xf in the area of it occurrence is P. spumarius. Transmission tests carried out with other xylem sap feeders found in the OQDS area are also discussed

Transcriptome profiling of two olive cultivars in response to infection by the CoDiRO strain of Xylella fastidiosa subsp. pauca

Background: The recent Xylella fastidiosa subsp. pauca (Xfp) outbreak in olive (Olea europaea) groves in southern Italy is causing a destructive disease denoted Olive Quick Decline Syndrome (OQDS). Field observations disclosed that Xfp-infected plants of cv. Leccino show much milder symptoms, than the more widely grown and highly susceptible cv. Ogliarola salentina. To determine whether these field observations underlie a tolerant condition of cv. Leccino, which could be exploited for lessening the economic impact of the disease on the local olive industry, transcriptional changes occurring in plants of the two cultivars affected by Xfp were investigated. Results: A global quantitative transcriptome profiling comparing susceptible (Ogliarola salentina) and tolerant (Leccino) olive cultivars, infected or not by Xfp, was done on messenger RNA (mRNAs) extracted from xylem tissues. The study revealed that 659 and 447 genes were differentially regulated in cvs Leccino and Ogliarola upon Xfp infection, respectively, whereas 512 genes were altered when the transcriptome of both infected cultivars was compared. Analysis of these differentially expressed genes (DEGs) shows that the presence of Xfp is perceived by the plants of both cultivars, in which it triggers a differential response strongly involving the cell wall. Up-regulation of genes encoding receptor-like kinases (RLK) and receptor-like proteins (RLP) is the predominant response of cv. Leccino, which is missing in cv. Ogliarola salentina. Moreover, both cultivars react with a strong re-modelling of cell wall proteins. These data suggest that Xfp elicits a different transcriptome response in the two cultivars, which determines a lower pathogen concentration in cv. Leccino and indicates that this cultivar may harbor genetic constituents and/or regulatory elements which counteract Xfp infection. Conclusions: Collectively these findings suggest that cv. Leccino is endowed with an intrinsic tolerance to Xfp, which makes it eligible for further studies aiming at investigating molecular basis and pathways modulating its different defense response

Draft Genome Sequence of CO33, a Coffee-Infecting Isolate of Xylella fastidiosa

The draft genome sequence of Xylella fastidiosa CO33 isolate, retrieved from symptomatic leaves of coffee plant intercepted in northern Italy, is reported. The CO33 genome size is 2,681,926 bp with a GC content of 51.7%

Infectivity and Transmission of Xylella fastidiosa by Philaenus spumarius (Hemiptera: Aphrophoridae) in Apulia, Italy

Discovery of Xylella fastidiosa from olive trees with "Olive quick decline syndrome" in October 2013 on the west coast of the Salento Peninsula prompted an immediate search for insect vectors of the bacterium. The dominant xylem-fluid feeding hemipteran collected in olive orchards during a 3-mo survey was the meadow spittlebug, Philaenus spumarius (L.) (Hemiptera: Aphrophoridae). Adult P. spumarius, collected in November 2013 from ground vegetation in X. fastidiosa-infected olive orchards, were 67% (40 out of 60) positive for X. fastidiosa by polymerase chain reaction (PCR) assays. Euscelis lineolatus Brulle were also collected but tested negative for the pathogen. Transmission tests with P. spumarius collected from the Salento area were, therefore, conducted. After a 96-h inoculation access period with 8 to 10 insects per plant and a 30-d incubation period, PCR results showed P. spumarius transmitted X. fastidiosa to two of five periwinkle plants but not to the seven olive plants. Sequences of PCR products from infected periwinkle were identical with those from X. fastidiosa-infected field trees. These data showed P. spumarius as a vector of X. fastidiosa strain infecting olives trees in the Salento Peninsula, Italy