Bertaccini, Assunta

‘Candidatus Phytoplasma cynodontis’ is widespread in bermudagrass and has only been found in monocotyledonous plants. Molecular studies carried out on strains collected in Italy, Serbia, and Albania enabled verification of molecular variability in the 16S ribosomal RNA (rRNA) gene. Based on restriction fragment length polymorphism and sequence analyses, the strains from Serbia were clearly differentiated from all others and assigned to a new ribosomal DNA (rDNA) subgroup designated as 16SrXIV-C. A system for amplification of fragments containing the ‘Ca. P. cynodontis’ groEL gene was developed to enable study of its variability in related strains belonging to different 16SrXIV subgroups. Despite the fact that the groEL gene exhibited a greater sequence variation than 16S rRNA, the phylogenetic tree based on groEL gene sequence analysis was highly congruent with the 16S rDNA-based tree. The groEL gene analyses supported differentiation of the Serbian strains and definition of the new subgroup 16SrXIV-C. Phylogenetic analyses of both genes confirmed distinct phylogenetic lineages for strains belonging to 16SrXIV subgroups. Furthermore, groEL is the only nonribosomal marker developed for characterization of ‘Ca. P. cynodontis’ thus far, and its application in molecular surveys should provide better insight into the relationships among these phytoplasmas and correlation between strain differentiation and their geographical distribution.

A phytoplasma was identified in naturally infected wild Balanites triflora plants exhibiting typical witches’ broom symptoms (Balanites witches’ broom: BltWB) in Myanmar. The 16S rRNA gene sequence revealed that BltWB phytoplasma had the highest similarity to that of ‘Candidatus Phytoplasma ziziphi’ and it was also closely related to that of ‘Candidatus Phytoplasma ulmi ’. Phylogenetic analysis of the 16S rRNA gene sequences indicated that the BltWB phytoplasma clustered as a discrete subclade with Elm yellows phytoplasmas. RFLP analysis of the 16S rRNA gene including the 16S–23S spacer region differentiated the BltWB phytoplasma from ‘Ca. P. ziziphi ’, ‘Ca. P. ulmi ’ and ‘Candidatus Phytoplasma trifolii ’. Analysis of additional ribosomal protein (rp) and translocase protein (secY) gene sequences and phylogenetic analysis of BltWB showed that this phytoplasma was clearly distinguished from those of other ‘Candidatus Phytoplasma ’ taxa. Taking into consideration the unique plant host and the restricted geographical occurrence in addition to the 16S rRNA gene sequence similarity, the BltWB phytoplasma is proposed to represent a novel taxon, ‘Candidatus Phytoplasma balanitae’.