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Liberibacter on carrot in the county of Halland, Sweden

A ProMED-mail post <http://www.promedmail.org>
ProMED-mail is a program of the International Society for Infectious Diseases <http://www.isid.org>

Date: October 2016

Source: European Plant Protection Organisation (EPPO) Reporting Service 10/2016/194 [edited] <http://archives.eppo.int/EPPOReporting/2016/Rse-1610.pdf>

The NPPO of Sweden recently provided EPPO with details about 'Candidatus Liberibacter solanacearum' (the potato haplotypes are listed in EPPO A1 List) on its territory (EPPO RS 2012/119). 'Ca. L.

solanacearum' was 1st found in 2011 in commercial fields of carrots (_Daucus carota_) in the county of Halland (Southern Sweden). 33 ha of carrot fields were investigated, and approximately 70 per cent of this area showed symptoms of 'Ca. L. solanacearum'. In these fields, the disease incidence ranged from 1 to 45 per cent.

The disease is transmitted by the carrot psyllid (_Trioza apicalis_) which is widespread in Europe. In the county of Halland, symptoms had been observed in carrot fields for several years but the identity of the pathogen was confirmed by molecular tests (PCR) in 2011 in carrot and psyllid samples.

Additional sampling has been carried out in the counties of Halland and Skåne, but testing results are not yet available. The source of this outbreak is unknown. No official phytosanitary measures were taken.

communicated by: ProMED-mail <promed@promedmail.org>

[Only a few members of _Candidatus_ Liberibacter have been characterised so far, including the pathogens causing citrus greening (huanglongbing, HLB; for more information see previous ProMED-mail posts in the archives). HLB, one of the most damaging diseases of citrus, is limited to these crops due to the host specificity of its vector, the citrus psyllid.

A new liberibacter species was found to be associated with zebra chip (ZC) and psyllid yellows (PY) diseases of potato, as well as a new yellowing disease of tomato and capsicum crops in New Zealand. The new pathogen was given the preliminary name of _Ca._ Liberibacter solanacearum (Lso; synonym _Ca._ L. psyllaurous). Lso has since also been associated with yellowing diseases of other solanaceous crops (physalis, tomatillo, aubergine, tamarillo, tobacco) and some crops in the family Apiaceae (carrot, celery). Main vectors of Lso are the potato psyllid (_Bactericera cockerelli_) in solanaceous host and the carrot psyllid (_Trioza apicalis_) in Apiaceae. These vectors have a much wider host range than the HLB vector and additional vector species are also being identified, further extending its potential host range and economic impact.

Currently the Lso species is divided into 4 haplotypes: A & B affecting Solanaceae, C & D affecting Apiaceae. Both groups of haplotypes have been reported from the Americas and New Zealand.

Carrot haplotypes have been reported previously from several other European countries (ProMED-mail posts

http://promedmail.org/post/20120713.1199961 &

http://promedmail.org/post/20151009.3702151) and northern Africa (ProMED-mail post http://promedmail.org/post/20141121.2978030), but potato haplotypes are still considered absent from the European/Mediterranean region.

Maps

Sweden (and neighbours):

<http://geology.com/world/norway-map.gif>

Swedish counties:

<http://www.worldatlas.com/webimage/countrys/europe/lgcolor/secounties.htm>

Europe, overview:

<http://www.edinphoto.org.uk/0_MAPS/0_map_europe_political_2001_enlarged.jpg>

Pictures

Lso affected carrot (compared with healthy):

<https://gd.eppo.int/media/data/taxon/L/LIBEPS/pics/1024x0/1939.jpg>

Zebra chip of potato:

<http://www.forestryimages.org/images/3072x2048/1490010.jpg> (plant) <http://www.dnature.co.nz/assets/Uploads/Liberibacter/Liberibacter.jpg>