Association of carrot psyllid (Trioza apicalis) with “Candidatus Liberibacter solanacearum” in Europe

Carrot psyllid (Trioza apicalis Förster) is a serious pest of carrots (Daucus carota L.) in northern and central Europe. Symptoms of psyllid damage in carrots include leaf curling, yellow and purple discoloration of leaves, stunted growth of shoots and roots, and proliferation of secondary roots. Carrots exhibiting symptoms were observed in commercial fields in southern Finland in 2008. Mechanisms by which carrot psyllid induces symptoms in plants are not understood and no plant pathogens have yet been associated with this insect. Given recent association of liberibacter with several crops affected by psyllids, an investigation on whether this bacterium is associated with carrot psyllid was conducted. PCR primer pairs OA2/OI2c and LsoF/OI2c, specific for the 16S rRNA gene from “Candidatus Liberibacter solanacearum”, generated amplicons of 1,168-bp and 1,173-bp, respectively, from DNA extracted from field-collected and laboratory-reared psyllids, and symptomatic carrots. In contrast, no PCR products were detected in DNA extracted from insect-free plants. The DNA sequences of amplicons of the genes encoding liberibacter 16S rRNA from psyllids and carrots were identical. The DNA of the 16S rRNA gene sequences determined from psyllids and carrots were over 99.9% identical to analogous sequences of “Ca. L. solanacearum” amplified from several solanaceous crops and the potato psyllid, vector of this bacterium. This is the first report of a plant pathogen associated with T. apicalis and the second known psyllid species associated with “Ca. L. solanacearum”.