Xylella fastidiosa is a vector-transmitted bacterial plant pathogen associated with serious diseases in a wide range of plants. It causes Pierce’s disease in grapevine, which is a major problem for wine producers in the United States and South America. X. fastidiosa was detected on olive trees in Puglia, southern Italy, in October 2013, the first time the bacterium has been reported in the European Union. Since then it has also been reported as present in France, Spain and Germany. Controls are in place to prevent the bacterium from spreading.
Numerous species of xylem sap-sucking insects are known to be vectors of the bacterium. X. fastidiosa also has a broad range of host plants, including many common cultivated and wild plants.
In June 2020, EFSA published guidelines for carrying out surveys of Xylella fastidiosa. The document guides plant pest surveyors through the design of statistically sound, risk-based surveys of the pathogen, integrating the key information gathered in the pest survey card for X. fastidiosa published in 2019.
In April 2020, EFSA published the latest update of its database of plants that act as hosts of Xylella fastidiosa. Thirty-seven additional species were identified as hosts of the pathogen, taking the total number of species in the database to 595.
Nell'ottobre del 2019 l'EFSA ha co-organizzato la seconda conferenza scientifica su Xylella fastidiosa. Circa 350 specialisti di salute delle piante provenienti da tutto il mondo si sono riunitiin Ajaccio, Corsica , per due giornate di intensi dibattiti su come la scienza possa contribuire a trovare soluzioni contro il patogeno delle piante che sta provocando danni ambientali ed economici in tutta Europa.
Nel giugno l’EFSA ha pubblicato una scheda di sorveglianza fitosanitaria su X. fastidiosa. La scheda è concepita per aiutare gli Stati membri a pianificare le proprie attività di indagine utilizzando un approccio statisticamente valido e basato sul rischio, in linea con gli orientamenti internazionali in materia di sorveglianza.
A maggio l'EFSA ha aggiornato la propria valutazione dei rischi da X. Fastidiosa per piante e colture dell’Unione europea. Il gruppo di esperti scientifici EFSA sulla salute dei vegetali si è avvalso di tecniche di modellazione computerizzata per simulare come X. fastidiosa si diffonda su brevi e lunghe distanze in diverse condizioni.
Nel settembre 2018 l’EFSA ha pubblicato l’ultimo suo aggiornamento della banca dati di piante di piante che fungono da ospiti di Xylella fastidiosa. L'elenco aggiornato include 563 specie vegetali individuate attraverso una nuova ricerca bibliografica e tramite le notifiche a EUROPHYT, il servizio UE di intercettazione fitosanitaria. È possibile accedere all'elenco che contiene dati grezzi su Knowledge Junction, il repertorio di evidenze e materiali di supporto EFSA utilizzati nelle valutazioni del rischio per la sicurezza alimentare o come serie di rapporti interattivi.
Nel luglio 2018 l'EFSA ha aggiornato la sua categorizzazione di X. Fastidiosa come organismo nocivo, già inserita nella valutazione del rischio fitosanitario pubblicata nel 2015. Il gruppo di esperti scientifici dell'EFSA sulla salute dei vegetali ha concluso che X. fastidiosa soddisfa i criteri per essere considerato “organismo nocivo da quarantena” nell’UE.
In April 2017, EFSA produced a report on the susceptibility of olive varieties to the Apulian strain of Xylella fastidiosa (subsp. pauca strain CoDiRO, ST53). The report noted that evidence from experimental infectivity studies and from surveys in olive orchards indicate tolerance of the Leccino variety to ST53. Tolerance or resistance traits have also been found in other olive varieties, such as FS-17®.
In November 2017, EFSA co-hosted a conference on the latest scientific developments surrounding X. fastidiosa. More than 250 plant health experts from around the world attended the event in Palma de Mallorca, Spain. The programme included around 50 presentations looking at issues such as current knowledge of the pathogen, how it is transmitted, resistance in plants and control measures.
In February 2016 EFSA’s database of host plants was updated to include 44 new species. The majority of the new species (70%) were identified in southern Italy (Apulia), Corsica and southern France (Provence-Alpes-Côte d'Azur region).
The following month EFSA published a report by the Italian National Research Council on the host range of X. fastidiosa CoDiRO, which confirmed that CoDiRO causes olive dieback.
In April, EFSA concluded that research being carried out in Apulia showed that certain treatments reduce the symptoms of disease caused by X. fastidiosa but do not eliminate the pathogen from infected plants.
EFSA’s experts concluded in August that there was no scientific evidence to indicate the presence of multiple types of X. fastidiosa in Apulia. They then reviewed new evidence regarding the categorisation of Vitis (grapevine), Citrus, Quercus ilex (holm oak) and Phoenix roebelenii (ornamental dwarf palm) as host plants of X. fastidiosa.
In January 2015 EFSA published a full pest risk assessment and evaluation of risk reduction options for X. fastidiosa in the EU. The scientific opinion included a list of host plants and European vectors of the bacterium. In March 2015, EFSA published a report categorising plants for planting, excluding seeds, according to the risk of introduction of X. fastidiosa.
In April EFSA responded to a claim by an Italian non-governmental organisation that a series of fungi – rather than X. fastidiosa – are the main causal agents of olive decline in Apulia. EFSA concluded that there was no scientific evidence that tracheomycotic fungi are the primary cause of olive die-back in Apulia.
A Scientific Opinion published by EFSA in September indicated that hot water treatment – whereby dormant plants and plant parts are submerged for 45 minutes in water heated to 50C – is a reliable method for controlling X. fastidiosa in dormant grapevine planting material.
In November 2015, more than 100 scientists from around the world attended a workshop hosted by EFSA to identify the main knowledge gaps and discuss research priorities for X. fastidiosa. In the same month, EFSA evaluated the results of ongoing studies and experiments carried out in Apulia, concluding that grapevine cannot be ruled out as a potential host of X. fastidiosa.
Following publication of EFSA’s advice, in February 2014 the European Commission put in place emergency measures to combat the spread and further introduction of the organism into the EU. These measures were further strengthened in May and October 2015.
In October 2013 Xylella fastidiosa was detected in olive trees in Lecce province in Apulia, Italy. It was the first outbreak of X. fastidiosa under field conditions to be reported in the European Union. In November of the same year EFSA provided the European Commission with urgent scientific advice and technical assistance on X. fastidiosa.
1. What is Xylella fastidiosa?
Xylella fastidiosa is a bacterial plant pathogen transmitted by insects that feed on xylem sap. It is associated with serious diseases in a wide range of plants around the world. For example, it causes Pierce’s disease in grapevine, citrus variegated chlorosis, phony peach disease, coffee leaf scorch, olive quick decline syndrome and other diseases that affect common trees such as plum, almond, oak and oleander.
2. Where is X. fastidiosa found?
Diseases caused by X. fastidiosa occur in tropical, sub-tropical and temperate areas. The bacterium is widespread in many areas of North, Central and South America and reached Europe in recent years. Official surveys carried out by EU Member States confirm so far that its presence is limited to Italy (southern Apulia), France (Provence-Alpes-Côte d'Azur and Corsica), Spain (Balearic Islands), and an isolated case in a greenhouse in Germany (Saxony).
3. How do plants become infected?
X. fastidiosa colonises the xylem network within plants. The main function of xylem vessels is to transport water from a plant’s roots to its leaves, so when the bacteria colonise the plant, the xylem vessels become blocked and the plant slowly dies. To reach a new host, X. fastidiosa has to be carried and transmitted by a vector – all xylem sap-feeding insects are potential vectors, until proven otherwise. The most common vectors worldwide are sharpshooter leafhopper (Cicadellinae), spittlebugs (Aphrophoridae) and froghoppers (Cercopidae). The meadow froghopper (Philaenus spumarius) is currently the only species confirmed to be a vector of the bacterium in Apulia.
4. What are the symptoms?
Symptoms range from leaf browning to plant death. The specific symptoms, sequence and pace of infection vary because of the wide range of potential host plants, the diversity of the pathogen and level of infection, as well as the different climatic conditions in areas where the bacterium is found. Many host plants infected with X. fastidiosa may not express any symptoms; other plants may show severe leaf scorching and wilting up to complete desiccation.
5. Which plants are vulnerable to attack by the bacterium?
EFSA maintains a database of known hosts, which currently lists 563 plant species – both naturally and experimentally infected hosts – from 82 botanical families. However, not all of the plants listed are susceptible to all “types” (subspecies or strains) of X. fastidiosa and, even when affected, plants will not necessarily become symptomatic. In addition, even plants belonging to the same species can express different levels of susceptibility depending on their variety and growing conditions. The identification of asymptomatic host species is crucial as they can act as symptomless carriers for this bacterium to new zones and more sensitive crops.
6. So is there more than one ‘type’ of Xylella fastidiosa?
Yes. There are five currently recognised sub-species of X. fastidiosa – fastidiosa, morus, multiplex, pauca and sandyi – which in turn have their own variants.
In Europe, the subspecies fastidiosa, associated with Pierce’s disease of grapevine and almond leaf scorch in the Americas, has been detected in the Balearic Islands in Spain, in isolated plants in a greenhouse in Germany (Saxony), and has been intercepted on some consignments of imported coffee plants. The subspecies multiplex has been reported in France (Corsica and Provence-Alpes-Côte d'Azur) and the Balearic Islands. The subspecies pauca, very common in South America, has been detected in Italy (Apulia), in the Balearic Islands, and in one isolated outbreak in France (Menton, Provence-Alpes-Côte d'Azur).
In addition, another species of Xylella, Xylella taiwanensis, occurs in Taiwan, where it causes pear leaf scorch. X. fastidiosa subspecies fastidiosa is also present in Taiwan.
7. What is being done to prevent the spread of X. fastidiosa in Europe?
8. What is EFSA’s role?
EFSA has published numerous reports and scientific opinions on X. fastidiosa since the beginning of the outbreak in southern Italy in 2013. In January 2015 EFSA published a full pest risk assessment and evaluation of risk reduction options for X. fastidiosa in the EU. The scientific opinion included a list of host plants and European vectors of the bacterium. Another significant output was the publication in March 2016 of a ;report by the Italian National Research Council on the host range of X. fastidiosa CoDiRO. This report was the result of an EFSA-funded pilot project aimed at assessing the host range of the Apulian strain of X. fastidiosa. The most crucial finding was confirmation that X. fastidiosa subsp. pauca (strain CoDiRO) is the causal agent of the olive dieback observed in Apulia. For full details of EFSA’s work in this area please see the “Completed work” section on this page.
 Complesso del Disseccamento Rapido dell’Olivo (Italian translation of olive quick decline syndrome)