'Candidatus Phytoplasma convolvuli', a new phytoplasma taxon associated with bindweed yellows in four European countries

Plants of Convolvulus arvensis var. linearifolius exhibiting symptoms of undersized leaves, shoot proliferation, and yellowing, collectively defined as bindweed yellows (BY) were sampled in different regions in Europe and assessed for phytoplasma infection by PCR amplification using phytoplasma universal rRNA operon primer pairs. Positive results were obtained for all diseased plants. RFLP analysis of amplicons comprising 16S rDNA alone or 16S rDNA and 16-23S intergenic spacer region indicated that detected phytoplasmas were distinguishable from all other previously described rDNA sequences. Analysis of 16S rDNAs derived from seven selected phytoplasma strains (BY-S57/11, BY-S62/11, BY-I1015, BY-I1016, BY-BH1, BY-BH2 and BY-G) showed that they were near identical (99.9-100% homology) but shared less than 97.5% identity with comparable sequences of other phytoplasmas. Thus, BY phytoplasmas represent a new taxon whose closest relatives are stolbur phytoplasma strains and 'Candidatus Phytoplasma fragariae' with which they share 97.2% and 97.1% 16SrDNA identity, respectively. Phylogenetic analysis of 16S rRNA gene sequences confirmed that BY phytoplasma strains collectively represent a distinct lineage within the phytoplasma clade and share a common ancestor with previously published or proposed 'Ca. Phytoplasma' species within a major branch including aster yellows and stolbur phytoplasmas.On the basis of unique 16S rRNA gene sequences and biological properties that include a host plant species and a geographic distribution limited to parts of Europe, the BY phytoplasmas represent a coherent but discrete taxon, 'Candidatus Phytoplasma convolvuli', with strain BY-S57/11 (accession number JN833705) as reference strain.