Update of the Xylella spp. host plant database - systematic literature search up to 30 June 2023.

This scientific report provides an update of the Xylella spp. host plant database, aiming to provide information and scientific support to risk assessors, risk managers and researchers dealing with Xylella spp. Upon a mandate of the European Commission, EFSA created and regularly updates a database of host plant species of Xylella spp. The current mandate covers the period 2021-2026. This report is related to the ninth version of the database published in Zenodo in the EFSA Knowledge Junction community, covering literature published from 1 January 2023 up to 30 June 2023, and recent Europhyt outbreak notifications. Informative data have been extracted from 47 selected publications. Seven new host plants were identified and added to the database. These plant species were naturally infected by X. fastidiosa subsp. multiplex in France, Spain and the United States. No additional data were retrieved for X. taiwanensis, and no additional multilocus sequence tipes (STs) were identified worldwide. New information on the tolerant/resistant response of plant species to X. fastidiosa infection were added to the database. The Xylella spp. host plant species were listed in different categories based on the number and type of detection methods applied for each finding. The overall number of Xylella spp. host plants determined with at least two different detection methods or positive with one method (between sequencing and pure culture isolation (category A), reaches now 439 plant species, 200 genera and 69 families. Such numbers rise to 696 plant species, 307 genera and 88 families if considered regardless of the detection methods applied (category E).

Update of the Xylella spp. host plant database - systematic literature search up to 31 December 2022.

This scientific report provides an update of the Xylella spp. host plant database, aiming to provide information and scientific support to risk assessors, risk managers and researchers dealing with Xylella spp. Upon a mandate of the European Commission, EFSA created and regularly updates a database of host plant species of Xylella spp. The current mandate covers the period 2021-2026. This report is related to the eighth version of the database published in Zenodo in the EFSA Knowledge Junction community, covering literature published from 1 July 2022 up to 31 December 2022, and recent Europhyt outbreak notifications. Informative data have been extracted from 21 selected publications. Twelve new host plants were identified and added to the database. Nine plant species were reported from Portugal and naturally infected by subsp. multiplex or unknown (i.e. not reported). Three plant species were successfully artificially infected by subsp. fastidiosa. No additional data were retrieved for X. taiwanensis, and no additional STs were identified worldwide. New information on the tolerant/resistant response of plant species to X. fastidiosa infection were added to the database. The overall number of Xylella spp. host plants determined with at least two different detection methods or positive with one method (between sequencing and pure culture isolation) reaches now 433 plant species, 197 genera and 68 families. Such numbers rise to 690 plant species, 306 genera and 88 families if considered regardless of the detection methods applied.

Update of the Xylella spp. host plant database - systematic literature search up to 30 June 2022.

This scientific report provides an update of the Xylella spp. host plant database, aiming to provide information and scientific support to risk assessors, risk managers and researchers dealing with Xylella spp. Upon a mandate of the European Commission, EFSA created and regularly updates a database of host plant species of Xylella spp. The current mandate covers the period 2021-2026. This report is related to the seventh version of the database published in Zenodo in the EFSA Knowledge Junction community, covering literature published from 1 January 2022 up to 30 June 2022, and recent Europhyt outbreak notifications. Informative data have been extracted from 30 selected publications. Fifteen new host plants were identified and added to the database. Those plant species were reported from Brazil, France, Italy, Portugal and Spain, and infected by subsp. multiplex, pauca or unknown (i.e. not reported). No additional data were retrieved for X. taiwanensis. Two new STs (namely ST88 and ST89) belonging to subspecies multiplex were identified in host plants in natural conditions, and new information on the tolerant/resistant response of plant species to X. fastidiosa infection were added to the database. The overall number of Xylella spp. host plants determined with at least two different detection methods or positive with one method (between sequencing and pure culture isolation) reaches now 423 plant species, 194 genera and 68 families. Such numbers rise to 679 plant species, 304 genera and 88 families if considered regardless of the detection methods applied.

Update of the Xylella spp. host plant database - systematic literature search up to 31 December 2021.

This Scientific report provides an update of the Xylella spp. host plant database, aiming to provide information and scientific support to risk assessors, risk managers and researchers dealing with Xylella spp. Upon a mandate of the European Commission, EFSA created and regularly updated a database of host plant species of Xylella spp. The current mandate covers the period 2021-2026. This report is related to the sixth version of the database published in Zenodo in the EFSA Knowledge Junction community, covering literature published from 1 July 2021 up to 31 December 2021, and recent Europhyt outbreak notifications. Informative data have been extracted from 29 selected publications. Eleven new host plants were identified and added to the database: six plant species naturally infected by subsp. multiplex of X. fastidiosa in the EU (France, Italy and Portugal) and five plant species artificially infected by different X. fastidiosa subspecies (multiplex, pauca, fastidiosa and sandyi). No additional data were retrieved for X. taiwanensis. New information on the tolerant/resistant response of plant species to X. fastidiosa infection were added, while no new STs have been identified worldwide compared to the previous update published in January 2022. The overall number of Xylella spp. host plants determined with at least two different detection methods or positive with one method (between: sequencing, pure culture isolation) reaches now 412 plant species, 190 genera and 68 families. Such numbers rise to 664 plant species, 299 genera and 88 families if considered regardless of the detection methods applied.

Update of the Xylella spp. host plant database - systematic literature search up to 30 June 2021.

Following a request from the European Commission, EFSA was asked to create and regularly update a database of host plant species of Xylella spp. The mandate now covers the period 2021-2026 and EFSA is requested to release an update of the database twice per year. The aim of the database is to provide information and scientific support to risk assessors, risk managers and researchers dealing with Xylella spp. This report is related to the fifth version of the database published in Zenodo in the EFSA Knowledge Junction community, covering literature published from 1 January 2021 up to 30 June 2021, and recent Europhyt outbreak notifications. Informative data have been extracted from 41 selected publications. Nineteen new host plants were identified and added to the database since the previous update published in June 2021. Those plant species were reported naturally infected by subsp. multiplex or unknown (i.e. not reported in the publication) of X. fastidiosa in the UE (France, Spain and Portugal). No additional data were retrieved for X. taiwanensis. New information on the tolerant/resistant response of plant species to X. fastidiosa infection were added, while no new STs have been identified worldwide compared to the previous update published in May 2021. The overall number of Xylella spp. host plants determined with at least two different detection methods or positive with one method (between: sequencing, pure culture isolation) now reaches 407 plant species, 185 genera and 68 families. Such numbers raise to 655 plant species, 293 genera and 88 families if considered regardless of the detection method applied.

Update of the Xylella spp. host plant database - systematic literature search up to 31 December 2020.

Following a request from the European Commission, EFSA was asked to create and regularly update a database of host plant species of Xylella spp. Complying with an extension of the previous mandate, which now covers the period 2021-2026, the current version of Xylella spp. host plant database updates the previous release dated April 2020. Informative data have been extracted from 86 recent publications retrieved through an extensive literature search. This report is related to the fourth version of the database published in Zenodo in the EFSA Knowledge Junction community, covering articles selected from: a systematic literature review conducted up to 31 December 2020, Europhyt outbreak notifications up to 18 March 2021 and communications from research groups and national authorities. Forty-three new host plant species of X. fastidiosa, identified through the data extracted from the selected publications, have been added to the database. Those plant species were reported as naturally or artificially infected by subsp. fastidiosa, multiplex, pauca or unknown (i.e. not reported in the publication) subspecies of X. fastidiosa. New information on the tolerant/resistant response of plant species or varieties to X. fastidiosa infection is also reported. No additional data were retrieved for X. taiwanensis. This new version of the database includes no update on the number of Sequence Types (STs) identified so far, which remains unchanged. The overall number of Xylella spp. host plants determined with at least two different detection methods or positive with one method (between: sequencing, pure culture isolation) reaches now 385 plant species, 179 genera and 67 families. Such numbers rise to 638 plant species, 289 genera and 87 families if considered regardless of the detection method applied. The database will be issued twice per year, with the aim to provide information and scientific support to risk assessors, risk managers and researchers dealing with Xylella spp.

Pest categorisation of beet necrotic yellow vein virus.

Following a request from the EU Commission, the Panel on Plant Health performed a categorisation of beet necrotic yellow vein virus (BNYVV), the causal agent of the sugar beet rhizomania disease. The virus is currently listed in Annex III as a protected zone (PZ) quarantine pest of the Commission Implementing Regulation (EU) 2019/2072. The identity of the BNYVV is well established. BNYVV is a soil-borne virus transmitted by the obligate root plasmodiophorid endoparasite Polymyxa betae. BNYVV is widely distributed in the EU, but is not reported in the following EU PZs: Ireland, France (Brittany), Portugal (Azores), Finland and Northern Ireland. The virus may enter, become established and spread in the PZs via P. betae resting spores with soil and growing media as such or attached to machinery and with roots and tubercles of species other than B. vulgaris and with plants for planting. Introduction of BNYVV would have a negative impact on sugar beet and other beet crops in PZs, because of yield and sugar content reduction. Phytosanitary measures are available to reduce the likelihood of entry and spread in the PZs. Once the virus and its plasmodiophorid vector have entered a PZ, their eradication would be difficult due to the persistence of viruliferous resting spores in the soil. The main knowledge gaps or uncertainties identified concerning the presence of BNYVV in the PZs and the incidence and distribution of BNYVV in Switzerland, a country to which a range of specific requirements do not apply. BNYVV meets all the criteria that are within the remit of EFSA to qualify as a potential protected zone union quarantine pest. Plants for planting are not considered as a main means of spread, and therefore BNYVV does not satisfy all the criteria evaluated by EFSA to qualify as potential Union regulated non-quarantine pest.

Update of the Scientific Opinion on the risks to plant health posed by Xylella fastidiosa in the EU territory.

EFSA was asked to update the 2015 EFSA risk assessment on Xylella fastidiosa for the territory of the EU. In particular, EFSA was asked to focus on potential establishment, short- and long-range spread, the length of the asymptomatic period, the impact of X. fastidiosa and an update on risk reduction options. EFSA was asked to take into account the different subspecies and Sequence Types of X. fastidiosa. This was attempted throughout the scientific opinion but several issues with data availability meant that this could only be partially achieved. Models for risk of establishment showed most of the EU territory may be potentially suitable for X. fastidiosa although southern EU is most at risk. Differences in estimated areas of potential establishment were evident among X. fastidiosa subspecies, particularly X. fastidiosa subsp. multiplex which demonstrated areas of potential establishment further north in the EU. The model of establishment could be used to develop targeted surveys by Member States. The asymptomatic period of X. fastidiosa varied significantly for different host and pathogen subspecies combinations, for example from a median of approximately 1 month in ornamental plants and up to 10 months in olive, for pauca. This variable and long asymptomatic period is a considerable limitation to successful detection and control, particularly where surveillance is based on visual inspection. Modelling suggested that local eradication (e.g. within orchards) is possible, providing sampling intensity is sufficient for early detection and effective control measures are implemented swiftly (e.g. within 30 days). Modelling of long-range spread (e.g. regional scale) demonstrated the important role of long-range dispersal and the need to better understand this. Reducing buffer zone width in both containment and eradication scenarios increased the area infected. Intensive surveillance for early detection, and consequent plant removal, of new outbreaks is crucial for both successful eradication and containment at the regional scale, in addition to effective vector control. The assessment of impacts indicated that almond and Citrus spp. were at lower impact on yield compared to olive. Although the lowest impact was estimated for grapevine, and the highest for olive, this was based on several assumptions including that the assessment considered only Philaenus spumarius as a vector. If other xylem-feeding insects act as vectors the impact could be different. Since the Scientific Opinion published in 2015, there are still no risk reduction options that can remove the bacterium from the plant in open field conditions. Short- and long-range spread modelling showed that an early detection and rapid application of phytosanitary measures, consisting among others of plant removal and vector control, are essential to prevent further spread of the pathogen to new areas. Further data collection will allow a reduction in uncertainty and facilitate more tailored and effective control given the intraspecific diversity of X. fastidiosa and wide host range.

Effectiveness of in planta control measures for Xylella fastidiosa.

This opinion updates the information included in the previous EFSA Scientific Opinion concerning the in planta control measures for Xylella fastidiosa, with a systematic review and critical analysis of the potential treatment solutions that have been published against this pest so far. The output of this opinion focuses on the application of chemical or biological treatments on living plants. In vitro studies, hot water treatments, use of resistant varieties and vector control are excluded from the review. The use of antibiotics is not considered due to the risk of antimicrobial resistance development. The use of weakly virulent or avirulent strains of X. fastidiosa is covered in this review, although this organism is an EU quarantine plant pest and its introduction in the EU territory is banned. Experiments were recently conducted to assess the effect of application of zinc, copper, and citric acid biocomplex, of N-acetylcysteine, and of 'diffusible signal factor' (and of its homologs). Their results showed that these control measures were sometimes able to reduce symptoms caused by X. fastidiosa. Recent experiments also showed that several species of endophytic microorganisms, some bacteriophages and inoculation of weakly virulent/avirulent strains of X. fastidiosa could offer some protection against the Pierce's disease. However, based on the reviewed results, the Panel concludes that, although several published experiments show some effects in reducing symptoms development, the tested control measures are not able to completely eliminate X. fastidiosa from diseased plants. The Panel confirms as previously stated that there is currently no control measure available to eliminate the bacteria from a diseased plant in open field conditions.

A New Resource for Research and Risk Analysis: The Updated European Food Safety Authority Database of Xylella spp. Host Plant Species.

Following a series of requests for scientific advice from the European Commission starting in 2013, the European Food Safety Authority (EFSA) conducted a pest risk assessment and created a comprehensive Xylella fastidiosa host plant database. The last update of the database, published in September 2018, includes information on host plants of both X. fastidiosa and X. taiwanensis, together with details on botanical classification, infection conditions, geographic location, pathogen taxonomy including information on subspecies, strain and sequence type, detection techniques, and tolerant/resistant response of the plant. This updated database of host plants of Xylella spp. reported worldwide provides a key tool for risk management, risk assessment, and research on this generalist bacterial plant pathogen.

Updated pest categorisation of Xylella fastidiosa.

Following a request from the European Commission, the EFSA Plant Health Panel updated its pest categorisation of Xylella fastidiosa, previously delivered as part of the pest risk assessment published in 2015. X. fastidiosa is a Gram-negative bacterium, responsible for various plant diseases, including Pierce's disease, phony peach disease, citrus variegated chlorosis, olive quick decline syndrome, almond leaf scorch and various other leaf scorch diseases. The pathogen is endemic in the Americas and is present in Iran. In the EU, it is reported in southern Apulia in Italy, on the island of Corsica and in the Provence-Alpes-Côte d'Azur region in France, as well as in the Autonomous region of Madrid, the province of Alicante and the Balearic Islands in Spain. The reported status is 'transient, under eradication', except for the Balearic Islands, Corsica and southern of Apulia, where the status is 'present with a restricted distribution, under containment'. The pathogen is regulated under Council Directive 2000/29/EC and through emergency measures under http://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX:32015D0789 (as amended http://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX:32017D2352). The pest could enter the EU via host plants for planting and via infectious insect vectors. The host range includes hundreds of host species listed in the EFSA host plant database. In the EU, host plants are widely distributed and climatic conditions are favourable for its establishment. X. fastidiosa can spread by movement of host plants for planting and infectious insect vectors. X. fastidiosa is known to cause severe direct damage to major crops including almonds, citrus, grapevines, olives, stone fruits and also forest trees, landscape and ornamental trees, with high impacts. The criteria assessed by the Panel for consideration as a potential Union quarantine pest are met (the pathogen is present in the EU, but it has a restricted distribution and is under official control). X. fastidiosa is not considered as a regulated non-quarantine pest (RNQP) as the pathogen may spread also via insect vector transmission.

Susceptibility of Olea europaea L. varieties to Xylella fastidiosa subsp. pauca ST53: systematic literature search up to 24 March 2017.

EFSA was requested by the European Commission to produce a report on the susceptibility of olive varieties to the Apulian strain of Xylella fastidiosa (subsp. pauca strain CoDiRO, ST53). A systematic literature search identified 21 references providing results of primary research studies on olive plants infected (naturally or artificially) by ST53. From experimental infectivity studies and from surveys in olive orchards, converging lines of evidence indicate tolerance of the Leccino variety to ST53 infections, although no long-term observations on yield are available yet. While the variety Leccino can become infected with the pathogen, it develops milder symptoms compared to those observed on susceptible varieties (e.g. Cellina di Nardò, Ogliarola salentina). Also, the size of the X. fastidiosa bacterial populations measured in Leccino-infected plants is lower compared to susceptible olive varieties. Preliminary results show that tolerance or resistance traits can also be found in other olive varieties. New research is now in place in the EU to study the level of susceptibility of many olive varieties to ST53 infections, therefore more relevant results will become available in the coming years.

Agroinoculation of Beet necrotic yellow vein virus†cDNA clones results in plant systemic infection and efficient Polymyxa betae transmission.

Agroinoculation is a quick and easy method for the infection of plants with viruses. This method involves the infiltration of tissue with a suspension of Agrobacterium tumefaciens carrying binary plasmids harbouring full-length cDNA copies of viral genome components. When transferred into host cells, transcription of the cDNA produces RNA copies of the viral genome that initiate infection. We produced full-length cDNA corresponding to Beet necrotic yellow vein virus (BNYVV) RNAs and derived replicon vectors expressing viral and fluorescent proteins in pJL89 binary plasmid under the control of the Cauliflower mosaic virus 35S promoter. We infected Nicotiana benthamiana and Beta macrocarpa plants with BNYVV by leaf agroinfiltration of combinations of agrobacteria carrying full-length cDNA clones of BNYVV RNAs. We validated the ability of agroclones to reproduce a complete viral cycle, from replication to cell-to-cell and systemic movement and, finally, plant-to-plant transmission by its plasmodiophorid vector. We also showed successful root agroinfection of B. vulgaris, a new tool for the assay of resistance to rhizomania, the sugar beet disease caused by BNYVV.

The benyvirus RNA silencing suppressor is essential for long-distance movement, requires both zinc-finger and NoLS basic residues but not a nucleolar localization for its silencing-suppression activity.

The RNA silencing-suppression properties of Beet necrotic yellow vein virus (BNYVV) and Beet soil-borne mosaic virus (BSBMV) cysteine-rich p14 proteins have been investigated. Suppression of RNA silencing activities were made evident using viral infection of silenced Nicotiana benthamiana 16C, N. benthamiana agroinfiltrated with green fluorescent protein (GFP), and GF-FG hairpin triggers supplemented with viral suppressor of RNA silencing (VSR) constructs or using complementation of a silencing-suppressor-defective BNYVV virus in Chenopodium quinoa. Northern blot analyses of small-interfering RNAs (siRNAs) in agroinfiltration tests revealed reduced amounts of siRNA, especially secondary siRNA, suggesting that benyvirus VSR act downstream of the siRNA production. Using confocal laser-scanning microscopy imaging of infected protoplasts expressing functional p14 protein fused to an enhanced GFP reporter, we showed that benyvirus p14 accumulated in the nucleolus and the cytoplasm independently of other viral factors. Site-directed mutagenesis showed the importance of the nucleolar localization signal embedded in a C4 zinc-finger domain in the VSR function and intrinsic stability of the p14 protein. Conversely, RNA silencing suppression appeared independent of the nucleolar localization of the protein, and a correlation between BNYVV VSR expression and long-distance movement was established.

Beet soil-borne mosaic virus RNA-4 encodes a 32 kDa protein involved in symptom expression and in virus transmission through Polymyxa betae.

Beet soil-borne mosaic virus (BSBMV), like Beet necrotic yellow vein virus (BNYVV), is a member of the Benyvirus genus and both are transmitted by Polymyxa betae. Both viruses possess a similar genomic organization: RNA-1 and -2 are essential for infection and replication while RNA-3 and -4 play important roles in disease development and vector-mediated infection in sugar beet roots. We characterized a new species of BSBMV RNA-4 that encodes a 32 kDa protein and a chimeric form of BSBMV RNA-3 and -4. We demonstrated that BSBMV RNA-4 can be amplified by BNYVV RNA-1 and -2 in planta, is involved in symptoms expression on Chenopodium quinoa plants and can also complement BNYVV RNA-4 for virus transmission through its vector P. betae in Beta vulgaris plants. Using replicon-mediated expression, we demonstrate for the first time that a correct expression of RNAs-4 encoded proteins is essential for benyvirus transmission.