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 Apulia, 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 Corsica and the Provence-Alpes-Côte d'Azur region of southern France. 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 March 2017 EFSA published a statement on the susceptibility of olive varieties to the Apulian strain of Xylella fastidiosa. A systematic literature search identified 21 references providing results of primary research studies on the susceptibility of olive plants to X. fastidiosa subsp. pauca strain ST53 (also known as CoDiRO).
EFSA has recently addressed a number of other questions related to the role of X. fastidiosa in the ongoing olive dieback outbreak in Apulia, southern Italy. EFSA’s experts concluded in August 2016 that currently there is 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.
Earlier in 2016 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 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.
What work has EFSA done in this area?
Xylella fastidiosa, a plant pathogenic bacterium, was detected in olive trees in Lecce province in Apulia, Italy, in October 2013, the first outbreak under field conditions in the European Union. The European Commission asked EFSA to provide urgent scientific and technical assistance on X. fastidiosa. In November 2013 EFSA published a Statement in which it reviewed the host plant range and vectors of the pathogen, the pathways for entry and spread, and the risk reduction options. This was followed in January 2015 by a comprehensive assessment of the risks to plant health of X. fastidiosa for the EU and the identification and evaluation of risk reduction options. For details of other work carried out by EFSA on X. fastidiosa please click the Milestones button on this page.
What were the main findings of EFSA’s risk assessment work?
EFSA’s Panel on Plant Health concluded in its January 2015 opinion that X. fastidiosa presents a major risk to the EU territory because host plants and vectors are present throughout the EU and there are regions with favourable environmental conditions. Outbreaks of this pathogen have led to severe losses of citrus in South America and grapes in North America.
X. fastidiosa has a very broad host range, including many cultivated and common plants in Europe. The organism may affect several crops in Europe, such as citrus, grapevine and stone fruits (almond, peach, plum), but also tree species and ornamental plants, such as oak, sycamore and oleander.
The strain of X. fastidiosa present in olive trees in Lecce province in Italy is very homogeneous, and identical to a variant infecting oleander in Costa Rica. X. fastidiosa has been associated in Lecce province with the quick decline syndrome of olive. Investigations showed that symptomatic olive trees were generally affected by a complex of pests and pathogens including X. fastidiosa, several fungal species belonging to the genera Phaeoacremonium and Phaemoniella, and Zeuzera pyrina (leopard moth). Up to now, the Apulian strain of X. fastidiosa has infected olive, almond, cherry, rosemary, oleander, myrtle, Italian buckthorn (Rhamnus alaternus), Spanish broom (Spartium junceum) coastal rosemary (Westringia fructicosa), myrtle-leaf milkwort (Polygala myrtifolia), wattle (Acacia saligna), dwarf periwinkle (Vinca minor) and rosy periwinkle (Catharanthus roseus).
All xylem sap-feeding insects in Europe are considered to be potential vectors of X. fastidiosa. Members of the insect families Cicadellidae, Aphrophoridae and Cercopidae are vectors in the Americas and, hence, should also be considered as potential vectors in Europe. The spittlebug Philaenus spumarius has been identified as a vector in Lecce province in Italy.
The two main pathways for entry of X. fastidiosa into a previously unaffected area are through trade of infected plants for planting, and the presence of infectious insects in plant consignments.
What about risk reduction options?
EFSA concluded that eradication of X. fastidiosa – i.e. its total elimination from an outbreak area – is unlikely to succeed in areas where the pest is widely established, because of the broad range of host plant and insect vector species. X. fastidiosa is established across tens of thousands of hectares in the Lecce province of Apulia.
However, using a combination of containment measures – such as preventing the movement of infected plants or infectious insect vectors, removing infected plants, controlling insect vectors and managing surrounding vegetation – could help to prevent or slow down the spread of the pest from Lecce province to neighbouring areas or other territories of the EU.
What were the recommendations of the EFSA Plant Health Panel?
The Panel recommended the continuation and intensification of research activities on the host range, epidemiology and control of the Apulian outbreak of X. fastidiosa. Based on the knowledge acquired by this research, uncertainties could be substantially reduced and a more thorough assessment of the risk and of the mitigation measures could be conducted for the Apulian strain of X. fastidiosa.
What is EFSA's role?
EFSA’s Panel on Plant Health provides independent scientific advice on the risks posed by plant pests to plants, plant products or biodiversity in the EU. The Panel reviews and assesses those risks with regard to the safety and security of the food chain.
The Panel carries out risk assessments – based on available scientific information and data – to produce scientific opinions and advice for risk managers in EU Member States or at the European Commission and the European Parliament.
Is further work being carried out?
EFSA is responding to all requests for scientific advice being made on this subject by the European Commission and is on stand-by to answer any further questions. Addressing the threat posed by Xylella fastidiosa to Europe’s plants and environment is a priority for us.
EFSA is maintaining and keeping up to date a database of plant species reported as hosts of Xylella fastidiosa. The Authority is also funding two outsourced research projects aimed at reducing the uncertainties identified in its risk assessment.
The Centre for Ecology and Hydrology (CEH) in the UK has explored the possibility of using a model to assess the potential spread of X. fastidiosa from the outbreak area in Lecce province, as part of a broader EFSA-funded project aimed at producing an inventory of mathematical models to predict the spread of exotic plant pests in the EU. This model could be further developed once the results of epidemiological research on X. fastidiosa in Apulia become available. The study was published on the EFSA website in April 2015.
An EFSA-funded pilot project by the National Research Council in Bari is studying the host range of the Apulian strain of Xylella fastidiosa. This will be concluded and published on the EFSA website by the end of 2015.
EFSA’s Plant Health Panel has also published a Scientific Opinion on the use of hot water treatment against X. fastidiosa on grapevines. The Panel concluded that the treatment – which is used successfully to eliminate the phytoplasma disease flavescence dorée from dormant grapevine planting material – is also effective against X. fastidiosa on grapevines.