ProMED
http://www.promedmail.org

Source: European and Mediterranean Plant Protection Organization (EPPO) Reporting Service 08/2024/176 [summ. Mod.DHA, edited]
https://gd.eppo.int/reporting/article-7926 and
https://doi.org/10.2903/j.efsa.2024.8898

EFSA [European Food Safety Authority] has recently published an update of its database on host plants of _Xylella fastidiosa_ (EPPO A2 List). EFSA regularly updates a database of host plant species of _Xylella_ spp. under a mandate of the European Commission.

The overall number of host plants naturally infected by _Xylella_ spp. and determined with at least 2 different detection methods, or positive with either sequencing or pure culture isolation reaches 451 plant species, 204 genera and 70 families. When considering plant species artificially infected or infected in unspecified conditions, this number reached 712 species.

Sixteen new host plants, 5 genera and 1 family were identified and added to the EFSA database as hosts of _X. fastidiosa_:
_Adenocarpus_ sp. (Fabaceae); _Ailanthus altissima_ (Simaroubaceae); _Carpinus caroliniana_ (Betulaceae); _Celtis_ sp. (Ulmaceae); _Cistus ladanifer_ (Cistaceae); _Coleonema album_ (Rutaceae); _Cytisus multiflorus_ and _C. striatus_ (Fabaceae); _Echinospartum lusitanicum_ (Fabaceae); _Halimium calycinum_, _H. lasianthum_, _H. ocymoides_ and _Halimium_ sp. (Cistaceae); _Prunus campanulata_ (Rosaceae); _Quercus prinus_ (Fagaceae); _Salix atrocinerea_ (Salicaceae).

They were naturally infected by _X. fastidiosa_ subsp. _fastidiosa_ or unknown subspecies either in Portugal or the United States. No additional data were retrieved for _X. taiwanensis_ and no additional multilocus sequence types (STs) were identified worldwide.

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Communicated by:
ProMED

[_Xylella fastidiosa_ (Xf) clogs the xylem of plants leading to wilting, necrosis and often death. It causes many serious crop diseases such as Pierce's disease of grapevine; leaf scorch of coffee, almond and olive; peach phony disease; plum leaf scald; citrus variegated chlorosis; lucerne dwarf; and leaf scorch of a range of other woody species. Latent infections of wild species as potential pathogen reservoirs have also been reported. A second species in the genus, _X. taiwanensis_, has recently been reported as the cause of a pear leaf scorch (see ProMED post 20181022.6105629).

Xf is spread by xylem-feeding insects, but also by grafting and with infected plant material. Moist conditions favour the vectors and therefore Xf-associated diseases. Disease management is difficult due to the large numbers of hosts and vectors and may include use of clean planting and grafting material, as well as vector control. Both the bacterium and its main vectors are of serious international quarantine concern. They are currently considered the most serious threat to European grape and fruit production.

Three subspecies have been formally accepted for Xf -- _fastidiosa_ (grapevine strain, Pierce's disease), _pauca_ and _multiplex_ -- but additional ones have been proposed. It appears that subspecies vary in host range, but more research is needed on susceptibility of different plant hosts to the different Xf subspecies; multiple Xf subspecies have also been found to be able to infect the same host species (e.g., both _pauca_ and _multiplex_ can affect olives). The initial European detection in olives was of ssp. _pauca_ in southern Italy, but all 3 ssp. have since been found in different European areas in a range of hosts. More information is urgently needed on distribution, epidemiology and the risks to different crops by Xf or its subspecies.

Pictures
Photo galleries of Xf symptoms & vectors, different hosts:
https://gd.eppo.int/taxon/XYLEFA/photos and via
https://www.forestryimages.org/browse/subimages.cfm?sub=647
Xf on almond:
https://iberianalmond.com/wp-content/uploads/2018/03/Xylella-fastidiosa-770x400.jpg,
https://www.pestcontrolmadrid.com/wp-content/uploads/2021/04/almonds-5349916-1280.jpg and
https://www.noticiasdejardim.com/wp-content/uploads/2020/07/xylella-fastidiosa-information-3.jpg
_P. spumarius_ vector:
https://www.sitkanature.org/photojournal/wp-content/gallery/20080810/20080810-philaenus_spumarius-1.jpg and
https://www.naturamediterraneo.com/Public/data9/geppe/IMG_0378_Detailr.jpg_2014520232022_IMG_0378_Detailr.jpg

Links
_X. fastidiosa_ diseases, diagnosis & vector information:
https://gd.eppo.int/taxon/XYLEFA (with current host list & distribution map),
https://www.bali.org.uk/help-and-advice/pests-and-diseases/xylella-fastidiosa/,
https://doi.org/10.1111/epp.12469 and
https://doi.org/10.1007/s00284-002-3785-7
Xf ssp _fastidiosa_ information & distribution:
https://gd.eppo.int/taxon/XYLEFF
Xf ssp _pauca_ information & distribution:
https://gd.eppo.int/taxon/XYLEFP
Xf strains and host range:
https://doi.org/10.2903/j.efsa.2020.6114,
https://doi.org/10.1111/ppa.12696,
https://doi.org/10.1007/s10658-019-01736-9,
https://doi.org/10.1094/PHYTO-11-14-0322-FI and
https://doi.org/10.1099/mic.0.000068
Xf resources and information via:
https://nature.berkeley.edu/xylella/
_X. fastidiosa_ taxonomy and strains:
https://www.uniprot.org/taxonomy/2371
EPPO A2 quarantine list:
https://www.eppo.int/ACTIVITIES/plant_quarantine/A2_list
Information on Xf vectors via:
https://bugguide.net/node/view/63
- Mod.DHA