Workshop on Xylella fastidiosa: knowledge gaps and research priorities for the EU


The plant pathogenic bacterium Xylella fastidiosa was detected in olive trees in Lecce province in Apulia, Italy, in October 2013 (Saponari et al., 2013). The Apulian strain of X. fastidiosa is considered to be a genetic variant within the subspecies pauca and identical (based on a sequence of 7 housekeeping genes) to a variant infecting oleander in Costa Rica (Nunney et al., 2014; Loconsole et al., 2016). This was the first field outbreak of X. fastidiosa in the European Union (EU) (Cariddi et al., 2014). Afterwards, since summer 2015, several outbreaks of X. fastidiosa belonging to a different subspecies group (i.e., multiplex) were reported from woody ornamental plants in Corsica and southern mainland of France. X. fastidiosa is one of the most dangerous plant pathogens worldwide, damaging major crops including fruit trees, grapevine and ornamentals. X. fastidiosa is a quarantine pest for the EU and emergency measures have been in place since its first outbreak in 2013.

In its Scientific Opinion published in January 2015, the Scientific Panel on Plant Health of the European Food Safety Authority (EFSA) conducted a detailed assessment of the risks to plant health for the EU territory posed by X. fastidiosa, including the identification and evaluation of risk reduction options, and recommended an intensification of research activities on the host range, epidemiology and control of the Apulian outbreak of X. fastidiosa (EFSA PLH Panel, 2015).

In May 2015, the European Parliament approved a non-legislative resolution demanding actions to halt the spread of the X. fastidiosa outbreak, including increased funding for research and increased international networking. To respond to the X. fastidiosa emergency needs, the European Commission (EC) has therefore reinforced research and innovation actions. A workshop entitled “Xylella fastidiosa: Options for its Control” was organised by the EC Directorate-General (DG) for Research and Innovation (RTD) at Expo in Milan in July 2015, to discuss with key experts the role that research and innovation can play in tackling the control of this bacterium (Anonymous, 2015). Specific research funding on X. fastidiosa topics have been made available by the EC within the EU framework programme for research and innovation Horizon 2020: the project Pest Organisms Threatening Europe (POnTE), including a work package on X. fastidiosa, was funded in November 2015, and a dedicated topic on X. fastidiosa was launched in the Sustainable Food Security 2016 call under Horizon 2020.

In September 2015, EFSA was tasked by the EC DG RTD to identify knowledge gaps and key priorities for research on X. fastidiosa in the EU, including the organisation of a scientific workshop, and to produce a periodical scientific report on the status of the biology, epidemiology and control of this pathogen.

Following this request, on 12-13 November 2015 in Brussels (BE), EFSA hosted a workshop entitled “Xylella fastidiosa: knowledge gaps and research priorities for the EU” in collaboration with the EC DG for Research and Innovation (RTD), Agriculture and Rural Development (AGRI), and Health and Food Safety (SANTE). The goal of this workshop was to facilitate scientific discussions and analyse knowledge gaps and priorities for EU research on X. fastidiosa. This report presents the outputs of the discussions at this workshop. The workshop, attended by about 130 participants (including scientists, risk assessors, risk managers, and stakeholders) from 16 EU countries and four non-EU countries, was structured through plenary sessions with presentations from keynote speakers and four discussion breakout sessions. Each breakout session focused on identification of knowledge gaps and research priorities on a different area of research: surveillance and detection (breakout Group 1); vectors identity, biology, epidemiology and control (breakout Group 2); plants: host range, breeding, resistance and certification (breakout Group 3); pathogen biology, genetics, characterization and control (breakout Group 4). The role of cropping practices and farming systems was also part of the discussion in the different breakout sessions. Each breakout session was introduced by short presentations from selected participants. All participants were expected to actively participate on identification and discussion of research topics. Abstracts of the plenary session and of the short presentations are available in the Appendix C of this report. Presentations of the plenary and breakout sessions and the recorded webstreaming of the plenary sessions can be downloaded from the workshop page on EFSA website.

In line with the conclusion of the previous workshop hosted by DG RTD in July 2015 (Anonymous, 2015), this workshop aimed to facilitate interaction among research groups to share previous experiences, establish new research collaborations, strengthen current collaborations among European and non-European research organizations, and to increase awareness about scientific work previously done elsewhere.

From the discussions in the breakout and plenary sessions, knowledge gaps and research priorities and opportunities were highlighted by the participants.

For surveillance and detection, it was stressed the importance of defining in advance why surveillance is needed. Already since the planning phase of a survey, there is a need to have defined a clear survey purpose. Can research improve the identification of targets (pathogen, vector, host, and pathways) and locations for surveillance? What are the best methods and periods for surveillance? Answers to these questions are likely to depend on improvement of the detection methods for the pathogen, especially during the latent period of infection, and of the knowledge on the underlying vector behaviours. Advanced remote sensing techniques could help in delimiting potential infected areas if survey resources are limited, however there could be a trade-off between size of area to be surveyed and sensitivity of detection methods. Research on survey design also can facilitate, by collection and analysis of survey data, the establishment of accurate disease/vector incidence and distribution maps, and a better understanding of epidemics and dispersal of X. fastidiosa. To facilitate research and enable data exchange and analysis across Member States, there is also a need for harmonisation of survey methods and sharing of data.

For research on vectors, the need for an inventory of potential vector species in the EU, including collection of biological and environmental data and geographical coordinates was highlighted, even more considering that vectors may not be pest species per se and hence their biology has been poorly studied so far. Insect rearing methods, knowledge of insect reproductive biology, feeding behaviours, population dynamics, host preference for feeding and reproduction, and the importance of studying the ecosystem as a whole were identified as key areas for research. This basic knowledge should then be translated into studies of pathogen transmission by vectors, vector infectivity in the field, and X. fastidiosa population dynamics. This in turn links with surveillance and monitoring. As the vectors are not general pests in their own right, there is also little experience with control methods, IPM, or on their effects on biodiversity. A general need of epidemiological research was highlighted to support both the development of integrated pest and disease management strategies and the risk management and containment measures to prevent spread.

For research on host plants, several questions were raised and discussed to identify knowledge gaps and research priorities. Should research on X. fastidiosa host range and plant genetic resources for breeding resistant varieties be general or specific? With newly-identified hosts, research may help to optimize certification schemes and procedures. Research on X. fastidiosa host range should be conducted to provide lists of host plants and also to help understand outbreaks as it relates to sources of inoculum in cultivated and non-cultivated habitats. It was recommended to complete the EFSA database on X. fastidiosa host plants by adding information on hosts of strains that have been characterized. There is need for research to test important EU crop varieties for susceptibility to infection by known X. fastidiosa strains from Europe (Italy and France), but also to representative strains from other clades that may invade Europe. For breeding of resistant or tolerant plant genotypes, the recommendation was to begin with olive trees by screening germplasm collections for tolerance or resistance to X. fastidiosa. Screening of germplasm collections should focus initially on commercially relevant varieties. If resistance/tolerance is not found within varieties or immediate lineages, then additional accessions should be tested. For certification of plant propagation material, there is need for research on diagnostic tools and sanitation methods. Multidisciplinary agro-ecological research was identified as a tool to investigate solutions to keep infected plants alive and economically viable in the outbreak areas where olives or other hosts contribute significantly to landscapes and old trees have a high cultural value.

With regard to the pathogen X. fastidiosa, discussion focused on the priorities for the EU, given the long history of X. fastidiosa research in the Americas, the timescale envisaged, the need for fundamental science, and socio-economic impact. In the short term, targets could be characterization of isolates from the European outbreaks and availability of reference collections. In the mid to long term, biotic and abiotic interactions, host specificity, host response to infection, and histopathology in new hosts were topics suggested and discussed. For research into pathogen control, there is need to address farmers’ expectations, especially in relation to physical approaches and methodologies of application of different tools and their integration.

As overall recommendations, it was stressed the need to establish an open-field laboratory in olive orchards affected by X. fastidiosa in Salento, where experiments could be conducted to develop strategies for disease and vector control, as well as studies on epidemiology and screening for tolerant or resistant genotypes. Best practices to optimise the research efforts, to promote interactions among participants, and to avoid research duplications were discussed and the following general suggestions were made: need for systematic reading of literature before designing new experiments; need to share information and data via free and centralized online databases, including ongoing research programmes; and need to provide a forum for international research meetings on X. fastidiosa and its vectors.

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First published in EFSA Supporting Publications
20 June 2016