Description of ‘Candidatus Phytoplasma meliae’, a phytoplasma associated with Chinaberry (Melia azedarach L.) yellowing in South America

Abstract

China tree yellows (ChTY) phytoplasma is associated with the yellowing disease of the China tree (Melia azedarach) in Argentina. According to partial 16S rRNA gene analysis, ChTY phytoplasma belongs to the 16Sr XIII group, subgroup G. Strains of species of ChTY have 98–99% 16S rDNA gene sequence similarity with 16SrXIII-group phytoplasmas, and less tan 97.5% when compared to all ‘Candidatus Phytoplasma’ described so far, except for the novel ‘Candidatus Phytoplasma hispanicum’. However, strains of species of ChTY are differentiated from the latter due to having additional molecular and biological attributes. The presence of unique features in the 16S rDNA sequence distinguishes ChTY from all species of ‘Candidatus Phytoplasma’ currently described. The in silico RFLP profile of 16S rDNA (1.2 kb) and rpLV-rpsC (1.3 kb) genes distinguished ChTY, as in the 16SrXIII-G subgroup within the 16SrXIIII group. The phylogenetic analyses, based on 16S rDNA, rpLV-rpsC and secA gene sequences, in addition to the restricted host range, characteristic symptoms and geographical distribution, confirm that the collective strains of the species ChTY represent a distinct lineage within the phytoplasma clade and support the description of a novel species of ‘Candidatus Phytoplasma meliae’ with the reference strain being ChTY-Mo3 (Montecarlo, Argentina).