EFSA 4th European Conference on Xylella fastidiosa - Report part 1
EFSA 4th European Conference on Xylella fastidiosa - Report part 1
In August 2023, the European Food Safety Authority (EFSA) held its 4th European Conference on Xylella fastidiosa in Lyon, France as a satellite event to the ICPP 2023. Experts from the BIOVEXO Project were key participants, alongside experts from the BeXyl project, ERC MultiX project, and the Euphresco network, as well as experts from a range of research institutions, and national and international bodies. This blog is the first in a series intended to provide an in-depth summary of the conference.
In August 2023, the European Food Safety Authority (EFSA) held its 4th European Conference on Xylella fastidiosa in Lyon, France as a satellite event to the ICPP 2023. Experts from the BIOVEXO Project were key participants, alongside experts from the BeXyl project, ERC MultiX project, and the Euphresco network, as well as experts from a range of research institutions, and national and international bodies. This blog is the first in a series intended to provide an in-depth summary of the conference.
The conference began on 19th August with a networking event and film screening, during which the documentary The Era of Giants was shown. The documentary charts the political, social, and personal impacts of the devastating discovery of Xylella in Apulia, Italy. The sense of loss, anger, fear, and resignation was tempered by messages of hope for a future in which we may learn to live with, or even beat Xylella. It was the perfect way to kick off the conference.
The conference proper got under way on 20th August with a full-day programme. The first session, entitled Current status and research updates on Xylella fastidiosa in the EU, consisted of 5 presentations (click on each to skip to the summary):
- Current pest status of X. fastidiosa in the European Union – Maria Belen Marquez Garcia, Directorate General for Health and Food Safety (DG SANTE), European Commission
- The current status of X. fastidiosa in Salento (Italy): are we approaching a new phase of the epidemic? – Donato Boscia, Institute for Sustainable Plant Protection (IPSP) of the National Research Council of Italy (CNR), Italy
- Comparative genomics of fastidiosa subsp. multiplex strains from France reveals pathogen dynamics after its introduction – Jessica Dittmer, National Institute for Agriculture, Food and the Environment (INRAE), France
- Xylella fastidiosa infection alters the xylem microbiota in wild and cultivated olive trees – Manuel Anguita-Maeso, University of North Carolina, United States, and Institute for Sustainable Agriculture (IAS) of the Spanish National Research Council (CSIC), Spain
- What is the risk of X. fastidiosa to establish in temperate European regions – a Belgian case study – Lena Pesenti, Université Catholique de Louvain (UCLouvain), Belgium
After a welcome and introduction from Giuseppe Stancanelli (EFSA), the first presentation of the conference was made by Maria Belen Márquez García (DG Sante), who set out the context and historical background of EU laws relating to Xylella, including main aspects of legislation and responsibilities on all EU Members States. Although, at present, the pathogen is only confirmed as present in 4 EU Member states, the law applies to all Members States. However, the European Commission is moving from a ‘one-size-fits-all’ approach, to a more bespoke system based on local and regional conditions.
Once it was realised that Xylella fastidiosa had become firmly established in the first outbreak zone, in Apulia, Italy, and was no longer eradicable, the National and European Phytosanitary Authorities established a ‘containment’ strategy under Commission Implementing Decision (EU) 2015/789. This legislation has subsequently been replaced by the key document on plant health, which came into force in December 2019, namely Regulation EU, 2016/2031. This was designed to Protect agriculture/horticulture/the environment in the EU from new plant pests; increase vigilance in relation to imports; and, improve early detection and action against pest outbreaks in the EU. The regulation defines different categories of pest, and its implementing regulation (2019/2072) defines Xylella as a Union Quarantine Pest, meaning it is “not present in the Union territory, or present but not widely distributed, and its establishment there would have unacceptable economic, social and environmental impacts”.
Subsequently, Xylella has been designated a priority pest (regulation 2019/1702). Specific measures against Xylella were then set out in Implementing Regulation (EU) 2020/1201. The key provisions of this legislation, specifically Articles 4-17, are summarized here.
Maria Belen Márquez García traced the development of EU measures alongside scientific understanding and EFSA guidance.
From January 2023, legislation has required all Members States (not only those where Xylella has already been detected) to carry out annual surveys according to EFSA guidelines and to establish contingency plans in case of confirmed/suspected cases. The new EPPO Bulletin includes Standard PM 7/24 (5): a Diagnostic Protocol for Xylella fastidiosa.
Maria Belen Márquez García explained how demarcated areas work: articles 7 to 11 of (EU) 2020/1201 state that, within an infected zone, all infected or symptomatic plants as well as other plants susceptible to Xylella must be removed. Additionally, all plants belonging to the same species as the infected plants (regardless of their current health status) must also be removed. Around the infected zone, a 2.5 km buffer zone must be established in which intensive surveillance and testing should take place and eradication measures applied. In the event that it is established that the infection is an isolated case, the buffer zone may be reduced to 1km. However, if it is confirmed that the pest has already spread and eradication will be impossible, the zone must be increased to a minimum of 5km (under articles 12 to 17).
The status of the demarcated eradication/containment zones was displayed, though in subsequent correspondence Maria Belen Márquez García stressed that, whilst the map is current as of summer 2023, it may change over time and the European Commission website, as well as the website of the National Competent Authority in the relevant EU Member State, should be consulted for the most up to date information.
Maria Belen Márquez García also explained rules for the importation and movement of plants from outside the EU, within the EU and between demarcated areas, infected zones, and buffer zones.
The second presentation was given by Donato Boscia (IPSP-CNR). He began by reminding the audience that October 2023 will mark the 10th anniversary of the first discovery of Xylella in Apulia, Italy. He outlined two trends that are now of particular interest:
i) Although the demarcated infected zone is a hundred times bigger than it was in 2013 (and is estimated to contain over 25 million olive trees), the northward spread of Xylella in the region has slowed dramatically and is mainly restricted to the Adriatic coast. There are likely to be multiple overlapping and interacting reasons for this, including a less suitable climate and strict phytosanitary control measures. Additionally, susceptible cultivars have been replaced by more resistant ones.
ii) In southern areas, there have been some signs of remittance in younger trees (up to 70 years of age) and some signs of the success of mitigation activities. In the South, new symptoms now appear to be milder. The reasons for this are under investigation; however, there is no evidence of any mutation of the Xylella subtype. Somewhat surprisingly, despite the apparently milder symptoms, there is also no evidence for a reduction in the bacterial titer in infected plants (though resistant cultivars naturally have a lower titer). The main factor in the South is likely to be the massive loss of vegetation, which has reduced the reservoir of inoculum and a consequently reduced rate of vector efficiency of transmission. All in all, this has meant a significant drop in the number of superinfections.
In subsequent email correspondence, he explained that ‘superinfections’ refers to bacteria boost (reinoculations) in already infected plants made by infected vectors: there is evidence that multiple reinfections of already infected plants can speed up the appearance, development, and severity of symptoms. He gave the example of century-old trees of cultivar Ogliarola near Gallipoli (Province of Lecce), which collapsed completely in two years, while in Oria (Province of Brindisi) trees of the same age and cultivar took six-seven year for the complete collapse of the canopy. A key major difference was the amount of the superinfections since, in Gallipoli, at that time, the vector population was much higher and with far higher percentage (over 80%) rate of infected insects than observed now, while in Oria the vector population was less abundant and had a significantly lower percentage of infected insects.
In his presentation, Donato Boscia showed that, in the area of Gallipoli, there has now been a clear reduction in the number of infected vectors. It is hypothesized that this could be at least one of the reasons behind the apparent reduction in severity of the disease.
The third presentation of session 1 was given by Jessica Dittmer (INRAE). She outlined the adaptive capacity of Xylella, noting that it had likely been introduced into France in the 1970s and 1980s without causing serious symptoms. Xylella’s current confirmed presence in four European countries (Italy, France, Spain and Portugal), due to accidental introduction of contaminated plant material, necessitates a better understanding of the evolutionary dynamics of the pathogen in its new areas of distribution.
She presented a comparative genomic analysis of strains of the subspecies multiplex isolated from various host plants in France since the first detection of the pathogen in 2015. Analysis of high-quality genome sequences, obtained using the PacBio sequencing technology, allowed the identification of numerous plasmids. This sets the French strains apart from American strains, which rarely possess plasmids.
The current status of Xylella in France was also described in a poster presented at the conference.
The fourth presentation was given by Manuel Anguita-Maeso, (IAS-CSIC) and was based upon the article Xylella fastidiosa Infection Reshapes Microbial Composition and Network Associations in the Xylem of Almond Trees (2022). He explained that research on vessel-associated microorganisms is gaining special interest as it could potentially reveal an innate natural defence mechanism enabling plants to cope with infection by xylem-inhabiting pathogens.
“Determination of the close-fitting associations between xylem-inhabiting microorganisms and X. fastidiosa may help to reveal specific microbial players associated with the suppression of ALSD [Almond Leaf Scorch Disease] under high X. fastidiosa inoculum pressure. These identified microorganisms would be good candidates to be tested in planta, to produce almond plants more resilient to X. fastidiosa infection when inoculated by endotherapy, contributing to [the suppression of] […] ALSD.” (Anguita-Maeso et al., 2022)
Plant-associated microorganisms are involved in several biotic and abiotic processes in the host, from the acquisition of nutrients to the increase of plant tolerance to abiotic stresses. Importantly, they also play a role in plant defence against pathogens. In this context, the acquisition and maintenance of an efficient microbiota capable of adapting more rapidly to a changing environment may confer a selective advantage. However, the relationship between Xylella and xylem sap microbiota remains understudied. He explained that his research has revealed the existence of negative associations between two of the most predominant bacterial genera inhabiting almond xylem vessels (i.e., Sphingomonas and Hymenobacter) and the presence of Xylella, as well as a general increase of Diplodia and Neofusicoccum fungi when Xylella was present. Based on this, he called for the potential of microbial endophytes to protect host plants from disease development and/or stimulate immunity to be investigated further.
In subsequent email correspondence, Manuel Anguita-Maeso explained the need for further research to confirm to what extent the observed positive and negative associations are due to: the displacement of the natural xylem microbiota due to niche exclusion (i.e. Xylella outcompetes the microbiota); an ability of Xylella to produce specific molecules with antimicrobial, signalling, and/or cell wall degrading activity; and/or, the triggering of host physiological responses that cause a decrease in specific components of the xylem microbiome. It is not yet known whether the causes are determined by a bio-marker, a factor of resistance, or other things.
The final presentation in the first session was given by Lena Pesenti (UCLouvain). She also presented a poster at the conference. In her talk, she underlined that, as Xylella has be shown to grow at relatively low temperatures, the risk to Northern Europe must not be underestimated. Accordingly, effective biosecurity measures and testing for early detection are important in northern regions too. For the same reason, research into potential plant hosts in northern regions is needed.
Her research has demonstrated that trees of the family Salicaceae can be effective host plants and, hence, could act as a reservoir and provide a means for Xylella to spread across temperate regions in Northern Europe. This was established through sentinel tests in Mallorca and through transmission experiments and dispersion capacity tests.
The videos and slides from the presentations are available on the #xylella23 Conference website. Additionally, the video includes the Q&A session that took place immediately after the presentations.
We hope you found this summary of the current status of Xylella in the EU interesting and informative. Our summary of the second session of the 4th European Conference on Xylella fastidiosa, the latest findings on Xylella fastidiosa resistance and control, will be published soon. If you’d like to follow the work of the BIOVEXO project and stay up to date on the fight against Xylella, please sign up to our Newsletter and follow us on Twitter, Linkedin, Instagram, or Facebook.
