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Source: A Punt [in Portuguese, machine trans., summ. Mod.DHA, edited]

The Citrus Management Committee of Portugal has announced that xylella was detected in December 2022 in citrus. The subspecies was identified as _Xylella fastidiosa_ ssp. _fastidiosa_, which has rarely been reported in this crop.

Xylella has been detected in Europe in 174 plant hosts [see links below], but this is the first time in the EU that it has been identified in citrus.
communicated by:
IBIS (International Biosecurity Intelligence System)

[_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 2nd 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 quarantine concern.

Xf had previously been reported mainly from the Americas, but now 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. Xf has been included on the A2 quarantine list of the European Plant Protection Organisation (EPPO).

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 of Xf or its subspecies.

Citrus variegated chlorosis (CVC) is a serious disease of citrus caused by Xf subsp. _pauca_. However, the effect of other ssp. on these hosts may not be identical. At the time of the 1st detection of Xf in Portugal on lavender in 2019 (ProMED post 20190114.6258392), a ssp. was not reported.

Europe, overview:

Photo galleries of Xf symptoms and vectors, different hosts: and via
CVC symptoms: and

_X. fastidiosa_ diseases, diagnosis and vector information: (with distribution map),,, and
Xf strains and host range:,,, and
Information on CVC and citrus strains:, and
Xf resources and information via:
_X. fastidiosa_ taxonomy and strains:
EPPO A2 quarantine list:
Information on Xf vectors via:
- Mod.DHA]


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