First report of ‘Candidatus Liberibacter solanacearum’ on carrots in France, in association with Trioza apicalis
The NPPO of France recently informed the EPPO Secretariat of the first record of ‘Candidatus Liberibacter solanacearum’ (EPPO A1 List – Solanaceae haplotypes*) in carrots (Daucus carota) on its territory. From March to June 2012, unusual symptoms characterized by poor crop growth and leaf yellowing started to be observed by growers in two fields (8;ha and 10 ha) of seed-producing carrots located in region Centre. In August 2012, the presence of ‘Ca. Liberibacter solanacearum’ was officially confirmed by the national reference laboratory (real-time PCR). Field observations showed that the disease affected approximately 50% of the area in the 8 ha-plot, and 90% in the 10 ha-plot. In addition, the presence of the carrot psyllid, Trioza apicalis (Homoptera: Psyllidae) was observed in infected fields. The origin of this infestation is unknown but the following three scenarios have been envisaged: 1) the pathogen was introduced with imports of infected carrot seeds from another country, thus supposing that the disease is seed-transmitted (which remains to be verified); 2) infected carrot psyllids were introduced via commercial exchanges and then spread the disease; 3) infected carrot seed lots were imported and grown, thus constituting a source for local populations of carrot psyllids to acquire and further transmit the disease. Phytosanitary measures have been taken and include the following:
- all seeds harvested from the two infested fields are kept in confined conditions for further studies, in particular on the possible seed transmission of ‘Ca. L. solanacearum’, and their commercialisation is prohibited;
- plant debris in infected fields have been buried;
- all machinery used to harvest infected seeds and bury plant material has been disinfected.
The pest status of ‘Candidatus Liberibacter solanacearum’ in France is officially declared as: Transient.
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* The Solanaceae haplotypes of ‘Ca. L. solanacearum’ associated with zebra chip disease, as well as their psyllid vector, Bactericera cockerelli (Hemiptera: Psyllidae), are absent from the EPPO region.
Sources
NPPO of France (2012-10).