Association of Candidatus Liberibacter solanacearum With the Psyllid, Trioza apicalis (Hemiptera: Triozidae) in Europe

The psyllid Trioza apicalis Forster (Hemiptera: Triozidae) is a serious pest of carrots, Daucus carota L., in Europe. Carrots exhibiting symptoms of psyllid damage were observed in commercial fields in southern Finland in 2008. Symptoms in affected plants included leaf curling, yellow and purple discoloration of leaves, stunted growth of shoots and roots, and proliferation of secondary roots. Mechanisms by which T. apicalis 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 T. apicalis was conducted. Polymerase chain reaction (PCR) primer pairs OA2/OI2c and LsoF/OI2c, specific for 16S rRNA gene from ''Candidatus Liberibacter solanacearum, generated amplicons of 1,168 bp and 1,173 bp, respectively, from DNA extracted from field-collected psyllids (61 and 36.6%, respectively), laboratory-reared psyllids (70 and 33.3%, respectively), field-collected petioles from symptomatic carrots (80 and 55%, respectively), and laboratory-grown carrots (100% for both primer pairs). 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. DNA of the 16S rRNA gene sequences determined from carrots and psyllids were 99.9% identical to analogous sequences of Ca. L. solanacearum amplified from several solanaceous crops and the psyllid Bactericera cockerelli (Sulc), a 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.