Candidatus Phytoplasma periplocae sp. nov. associated with Periploca aphylla witches’ broom disease

Periploca aphylla witches' broom (PapWB) is a phytoplasma-associated disease first reported in south-western Iran in 2010. Recent observations showed that the disease is spreading to new areas. PapWB phytoplasmas, detected in symptomatic P. aphylla plants, exhibited identical nucleotide sequences in the 1.8 kb PCR amplicon encompassing the 16S rRNA gene, the 16S-23S spacer region and the 5'-end of the 23S rRNA gene. When compared with the reference strains of previously described 'Candidatus Phytoplasma' species, the selected representative strain PapWB-S exhibited the highest 16S rRNA gene sequence identity (98.15%) with salt cedar witches' broom (SCWB1) phytoplasma, the reference strain of 'Ca. P. tamaricis'. Moreover, the sequence identity values for the tufB, rplV-rpsC and secY genes of PapWB-S strain, when compared with those of reference strains of previously described 'Ca. Phytoplasma' species, were below the thresholds adopted for describing new species. Phylogenetic analyses confirmed the close relationship of the strain PapWB-S with SCWB1 followed by other 'Ca. Phytoplasma' species belonging to the ribosomal groups 16SrX, 16SrXX and 16SrXXXIII. Following the revised guidelines for describing 'Ca. Phytoplasma' species, 'Ca. P. periplocae' sp. nov., associated with PapWB disease, is proposed, and the 16S rRNA gene sequence (accessible at GenBank/NCBI accession number OQ819043) is its nomenclatural type.