Genetic Variation of 'Candidatus Liberibacter solanacearum' Haplotype C and Identification of a Novel Haplotype from Trioza urticae and Stinging Nettle

'Candidatus Liberibacter solanacearum' (CLso) haplotype C is associated with disease in carrots and transmitted by the carrot psyllid Trioza apicalis. To identify possible other sources and vectors of this pathogen in Finland, samples were taken of wild plants within and near the carrot fields, the psyllids feeding on these plants, parsnips growing next to carrots, and carrot seeds. For analyzing the genotype of the CLso-positive samples, a multilocus sequence typing (MLST) scheme was developed. CLso haplotype C was detected in 11% of the T. anthrisci samples, in 35% of the Anthriscus sylvestris plants with discoloration, and in parsnips showing leaf discoloration. MLST revealed that the CLso in T. anthrisci and most A. sylvestris plants represent different strains than the bacteria found in T. apicalis and the cultivated plants. CLso haplotype D was detected in 2 of the 34 carrot seed lots tested, but was not detected in the plants grown from these seeds. Phylogenetic analysis by unweighted-pair group method with arithmetic means clustering suggested that haplotype D is more closely related to haplotype A than to C. A novel, sixth haplotype of CLso, most closely related to A and D, was found in the psyllid T. urticae and stinging nettle (Urtica dioica, Urticaceae), and named haplotype U.