EFSA 4th European Conference on Xylella - Report part 4
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 fourth and final in a series intended to provide an in-depth summary of the conference.
After session 1, on the Current status and research updates on Xylella fastidiosa in the EU, session 2, on the latest findings on Xylella fastidiosa resistance and control, and session 3, on Xylella fastidiosa vectors biology, the final session, session 4, looked at Tools for Xylella fastidiosa surveillance and detection.
Session 4 consisted of 6 presentations (click on each below to skip to the summary), followed by an open Q&A discussion:
- Use of plasmid profiles in epidemiological surveillance of X. fastidiosa outbreak in the Valencian Community, Spain – Maria del Pilar Velasco Amo, Institute for Sustainable Agriculture (IAS) of the Spanish National Research Council (CSIC), Spain
- Early detection of fastidiosa infection using reflectance proximal sensors in almond and olive trees – Miguel Román-Écija, Institute for Sustainable Agriculture (IAS) of the Spanish National Research Council (CSIC), Spain
- Detection of symptoms induced by fastidiosa with high-resolution multispectral satellite data: assessment with airborne hyperspectral imagery – Pablo Zarco-Tejada, University of Melbourne, Australia
- RiPEST: EFSA develops a tool for designing more robust and harmonized pest surveys in the EU – Alice Delbianco, European Food Safety Authority (EFSA)
- Delimiting survey of fastidiosa subsp. multiplex: bringing together multidisciplinary expertise to support risk management – Pauline De Jerphanion, French General Directorate for Food (DGAL), French Ministry of Agriculture, and French Epidemiological Plant Health Surveillance Platform, France
- Evaluation of outbreak response plans for fastidiosa in Alicante, Spain – Martina Cendoya, Valencian Institute for Agricultural Research (IVIA), Spain
Maria del Pilar Velasco-Amo (IAS-CSIC) began by explaining that, since Xylella was first detected in almond trees in Alicante in 2017, the demarcated area has expanded to cover over 145,000 hectares. To date, only one sequence type of Xylella has been detected in the region, Xylella fastidiosa subsp. multiplex ST 6. It has been detected in 26 different host plants, but over 90% of infections have been in almond trees (Prunus dulcis).
The role of plasmids in the Xylella life cycle, and their effects on adaptation to new environments/hosts, has been the subject of the investigation. Their studies have revealed that four plasmid profiles were present in strains of Xylella fastidiosa subsp. multiplex ST 6 isolated in the Demarcated Area of the Valencian Community, which exhibit different geospatial clustering. They suggested that plasmid profiling of Xylella strains can contribute to epidemiological surveillance, a to better understanding of Xylella’s spread.
Miguel Román-Écija (IAS-CSIC) started by reminding the audience of the difficulty of detecting Xylella in its early stages of infection, due to lengthy incubation periods, which causes complications for disease control measures. He explained that chemical and structural changes in the composition of leaves on infected plants can be detected and serve as an indicator before symptoms become visible to the eye. These chemical and structural changes can be detected via vegetation indices and pigment content acquired by proximal spectral sensors on plant leaves. This method has been tested in artificially inoculated olive plants under greenhouse conditions and in naturally infected almond trees in the field.
He showed that infections could be detected even in the absence of visible symptoms. Interestingly, differences could also be detected between infected and non-infected trees in rain-fed and irrigated almonds. Some variation was also observed between rates of detection in different olive cultivars.
He concluded by summarising that the use of proximal spectral sensors could enable early detection of Xylella fastidiosa in asymptomatic plants, providing a valuable tool for disease monitoring and plant breeding.
In contrast to the proximal spectral sensors employed by Miguel Román-Écija, Pablo Zarco-Tejada (University of Melbourne) presented the ability of spectral sensors to detect Xylella infections from the air, using high-resolution multispectral satellite data. Work began on airborne detection methods for Xylella in 2016 as part of the POnTE Project. By 2018, they had demonstrated that they could employ airborne sensors to detect Xylella with an 80% accuracy rate even before visible symptoms appeared.
However, remote sensing using satellite imagery, whilst able to detect intermediate and advanced stages of Xylella infection, was less able to detect early stages of infection accurately. The natural variability in water a nutrient stress is one element that complicates multispectral sensing. By 2021, a protocol had been successfully developed to account for variability in abiotic stress factors.
New satellites with sensitivity to spectral bands including SIF, blue NPQI, anthocyanins, and xanthophylls, may offer the potential for increased sensitivity and resolution, bringing satellite multispectral imaging up from accuracy levels of around 70% to similar levels as airborne hyperspectral imaging (around 90%).
Alice Delbianco (EFSA) began her presentation by reminding the audience that, since 2017, the European Union has mandated the provision of a toolkit to allow Members States to plan and execute statistically sound and risk-based surveys of quarantine pests. Quarantine pests are set out in Annex II to Commission Implementing Regulation (EU) 2019/2072 of 28 November 2019. To date, EFSA has published Pest Survey Cards for around 100 pests, including Xylella. For each pest, the cards provide details on where, when, how, and what to survey for. There are also both general and specific guidelines for the design and methodology of the surveys. Finally, the toolkit includes a statistical calculator to estimate sample sizes; however, the latter previously lacked any step-by-step guidance. Alice Delbianco explained that EFSA has now developed a new tool, tailored to plant health, which guides the user through each step of the survey: RiPEST. RiPEST is freely available on the EFSA website – all you need to do is log in.
Alice Delbianco proceeded to give a demonstration of the tool using Xylella fastidiosa as an example, which can be viewed in the video recording of the session on the EFSA #Xylella23 webpage. Additionally, a poster on how to maximise the method sensitivity for the surveillance of Xylella fastidiosa was included as part of the poster exhibition. Once the survey has been completed, the RiPEST tool will also calculate the confidence level for any results / conclusions and allow the report to be downloaded as a excel and pdf file, which can then be uploaded to the EUROPHYT Survey platform. Finally, Alice Delbianco informed the audience that EFSA is also working on developing multi-pest surveys at the crop level. It is currently in the pilot phase and should be available by the end of 2023.
Pauline De Jerphanion (DGAL) introduced work by French Epidemiological Plant Health Surveillance Platform and the French Ministry of Agriculture on bringing together multidisciplinary expertise to support risk management within the context of a delimiting survey of Xylella fastidosa subsp. Multiplex in France. Xylella has been detected in three regions of France: Corsica and Provence-Alpes-Côte d’Azur, where it has been present since 2015, and Occitanie, where it was first detected in 2020. Following reinforced surveillance and the rapid expansion of the demarcated area in Occitanie, the French Ministry of Agriculture appointed a multidisciplinary working group to assist with delimitation of the affected area.
This group found that, within the infected areas and the buffer zone, the bacterium was already widely established in the semi-natural natural environment, with two plant species identified as indicators of its presence, Spanish broom (Spartium junceum) and wild almond (Prunus dulcis). They identified agricultural wasteland and semi-natural areas close to infrastructure such as railway and motorway embankments as environments favourable to host plants, especially Spartium junceum, and the bacterium’s main vector, Philaenus spumarius. Xylella was also detected in urban areas.
A risk map was produced based on land use and eco-climate data. This led to the imposition of a 10km border area around the 35km containment zone centred on identified infections. Within this border area, a sequential adaptive strategy was adopted and over 9000 samples were taken, from 182 sites of 2km² (calculated using EFSA’s RiBESS+ tool). Six samples were found to be positive for Xylella across 4 sites. A second round of testing on 500m² sites at these 4 sites resulted in between 1 and 10 positive samples. A third round of testing on 100m² plots is on-going.
She concluded that the multidisciplinary and collaborative approach had been successful and led to a constant improvement of the risk analysis and use of different survey methods for surveillance. She also noted the continuing need for further research into the origin of the initial infection in Occitanie, the behaviour of vectors, and the potential impact of climate change and water stress on the spread and impact of the bacterium.
Martina Cendoya finished the session by reporting the outbreak response plans for Xylella fastidiosa in Alicante, where Xylella was first detected in 2017. According to EU regulations, mandatory annual surveys must be performed once an outbreak is detected. Martina Cendoya simulated the spread of almond leaf scorch disease (ALSD) in Alicante, Spain and evaluated the effectiveness of two survey designs to manage the outbreak: a one-step approach based on the total number of trees and a two-step approach estimating the sample size per hectar and then the number of hectars subject to inspection. Whilst it involves considerably greater effort, a two-step approach has been proven to be significantly more effective/efficient. Moreover, reducing the transmission rate in the buffer zone significantly increased the efficiency of the control measures.
We hope you found this summary of the session on Tools for Xylella fastidiosa surveillance and detection interesting and informative. The session closed with a Q&A session, which can be viewed in the video of session 4. Slides from all the presentations are available on the #xylella23 Conference website.
After the Q&A session, Giuseppe Stancanelli (EFSA) and Blanca Landa (Bexyl Project, CSIC/IAS) led a closing panel of the session chairs from session 1, session 2, and session 3 in giving closing remarks. Blanca Landa reiterated the fast-moving regulatory landscape as well as changes in the progress of the bacterium in Italy. She emphasised the continued need for further research: “We need to understand not only the genetics of the plant, but also the microbiome of the plant and the role that it can play in [the development of] Xylella symptoms.” Furthermore, she warned against overlooking the threat the pathogen could pose to Northern Europe.
Stéphane Compant (BIOVEXO Project, AIT) added that research on control has shown some promising results, which gives reason for optimism; but cautioned that up-scaling remained a challenge. Maria Saponari noted the difficulties in finding natural resistance to disease, but that two olive cultivars have shown resistance to Xylella. Energy is being invested in screening and breeding programmes. Stéphane Compant called for further research into the mechanisms and interacting factors that confer resistance.
Astrid Cruaud emphasised the value of modelling, though stressed the complexity of forming strategies for vector control due to variations in micro-climate, vector behaviour etc. She also expressed some concern that the focus remains very tightly oriented towards Philaenus Spumarius whilst other vectors and potential vectors remain understudied. Rodrigo Almeida noted interesting work being done in the US and Brazil and that research into transmission is less common in Europe, though Blanca Landa replied that this was due to the lack of secure phytosanitary facilities that would permit this.
Valérie Grimault asked whether multispectral sensors and surveillance tools could also be used for resistance testing and biome control evaluation. She stressed the importance of well-designed surveys. Claude Bragard commented that coordination and harmonisation of pest surveillance are vital but expressed concern that not enough resources seemed to be being put into at-risk areas where Xylella has not yet been detected.
Finally, Giuseppe Stancanelli concluded that the conference “highlighted preparedness and early detection as key tools in the fight against Xylella fastidiosa, while showcasing the tangible results that EU-funded research is delivering against major threats to Europe’s agricultural and environmental heritage”.
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