Plant health: Xylella fastidiosa outbreak in Italy and damages to olive trees

Xylella fastidiosa is a bacterium in the class Gammaproteobacteria, is an important plant pathogen that causes phoney peach disease in the southern United States, bacterial leaf scorch, oleander leaf scorch, and Pierce’s disease, and citrus variegated chlorosis disease (CVC) in Brazil.

Recently found for the first time on EU territories, the strain of Xylella fastidiosa identified in Italy (province of Lecce, in the Apulia region) attacks mainly olive trees, which show leaf scorching, branch desiccation and quick decline symptoms, leading in the most severe cases to the death of the trees. Olive cultivation is widespread throughout the Mediterranean region and is vital for the rural economy, local heritage and the environment.

On November 2013, EFSA provided urgent advice to the Commission, stating that:

“Transmitted by certain types of sap-sucking hopper insects, the bacteria X. fastidiosa, has been identified in the current disease outbreak that has affected 8000 hectares of olive trees in the Puglia region of Southern Italy.  The bacteria can be hosted in a very broad range of plants including almond, peach, plum, apricot, grapevines, citrus, coffee and olive as well as oak, elm, Ginkgo and sunflower. Importantly, plants can carry the bacteria without showing signs of disease.

X.fastidiosa is regulated as a harmful organism in the European Union (EU), whose introduction into, and spread within, all Member States is banned. In light of the current outbreak, the European Commission requested EFSA to provide urgent scientific advice outlining the list of known plant hosts, identifying the different ways that infected plant species and carrier insects could enter the EU as well as identifying and evaluating possible preventive measures.

Plant health experts at EFSA have concluded that X. fastidiosa has a very broad range of known host plants in the EU, including many grown for agricultural production as well as indigenous wild species common in Europe.  Additionally, there are a large number of species that could potentially be infected by the bacteria but have never been exposed, making it difficult to establish what the likely impact would be.  Importantly, the sap-sucking hopper insects found in the EU that could potentially carry the disease are likely to have different feeding habits and patterns. As the only natural means for spreading X. fastidiosa is by the sap-sucking hopper insects that generally can fly short distances of up to 100 metres, movement of infected plants for planting is the most efficient way for long-distance dispersal of X. fastidiosa. In addition, the transport of the insects that carry the bacteria in plant shipments and consignments has been identified as a concern.  The main source of X. fastidiosa into the EU is therefore trade and thereafter the movement of plants intended for planting.

Other potential sources of infection were assessed including fruit, wood, cut flowers, seeds and ornamental foliage. However, these were considered either negligible or low in terms of potential pathways for introduction of the bacteria. There is no record of successful eradication of X. fastidiosa once it has been established outdoors.

EFSA therefore recommends that preventative strategies for containment of outbreaks should focus on the two main routes of infection (plants for planting and infective insects in plant consignments) and be based on an integrated system approach.”

Following this rapid assessment, EFSA’s Plant Health Panel will conduct a comprehensive assessment of the risk posed by this bacteria Xylella fastidiosa to the EU crops and plants. In February 2014, on the ground of emergency the EU adopted the Commission Implementing Decision of 13 February 2014 as regards measures to prevent the spread within the Union of Xylella fastidiosa (Decision 2014/87/EU).

The measures provide conditions on the import and movement of particular plants which host, or are likely to host this bacterium, its timely identification in the affected areas as well as its eradication. They include obligations to notify any outbreak, official annual surveys, demarcation of infected areas, sampling, testing and monitoring, and removal and destruction of infected plants.

Here above you can find, finally, the FVO report (just published) of an audit performed in Italy from 10th to 14th February 2014, assessign the situation. The findings are not so positive and the audit team issued 10 recommendations to the Competent Authorities:

“The objective of the audit was to evaluate the situation and official controls for Xylella fastidiosa (Well and Raju) (hereafter “Xf”). This organism is listed as a harmful organism in Annex I, Section A, Part I of Council Directive 2000/29/EC, which means that it is not present in the EU and if found, Member States must eradicate it, or if that is impossible, inhibit its spread.

It was identified in the Lecce province in the Puglia region of Italy in October 2013. As part of a complex of harmful organisms it has caused devastating die back in olive groves over a substantial area in Lecce. In view of the seriousness of this organism and the potential risk to the EU, this audit was added to the FVOs planned 2014 audit programme.

The audit found that, the competent authorities have taken significant steps since the finding of a new strain of Xf (Salento strain) in Lecce province, in October 2013. Based on regional legislation, adopted in 2013, measures are in place establishing conditions for the production and movement of plants for planting in nurseries located in Lecce province. An extensive survey activity is still being carried out in order to delimit the spread of the disease in the province and to define infected and buffer zones. However, significant parts of the survey were not carried out in the most favourable time of the year. The survey is planned to be concluded by the end of March 2014.

No eradication or containment measures have been taken and the disease has spread very rapidly. Diseased trees are left in place, acting as a reservoir of infection. Unless action is taken, further rapid spread of the disease must therefore be anticipated.

The ELISA test for plant species other than olive is not yet fully reliable. In addition, the testing of dormant woody material (e.g. Vitis) during the winter and the limited sample sizes used also affect the reliability of the testing. In these circumstances, there is a risk of obtaining false negative results. Until this is addressed the authorities cannot say for sure that plants listed in the annexes of Decision 2014/87/EU are actually free from Xf prior to permitting their movement within the EU.

This represents a potential risk of spreading the organism to other parts of Italy and to other Member States. Although research work has been carried out and is continuing, key factors regarding the epidemiology of Xf remain to be clarified”