Summary auto-generated
Researchers detected a previously undescribed phytoplasma in Australian grapevines exhibiting yellows disease symptoms. Using PCR targeting phytoplasma DNA and restriction fragment length polymorphism (RFLP) analysis of the 16S rRNA gene, they identified this pathogen as taxonomically distinct from known phytoplasmas. The Australian grapevine yellows phytoplasma was classified as a new subgroup (16SrI-J) within the group 16SrI of phytoplasmas. Phylogenetic analysis of 16S rRNA sequences revealed the pathogen belongs to a separate subclade (subclade xii), most closely related to the stolbur phytoplasma but clearly distinguished by unique sequences and restriction site patterns. The researchers proposed the formal name "Candidatus Phytoplasma australiense" for this organism. Detection was confirmed in all diseased grapevines tested but absent in healthy plants. This work demonstrates that Australian grapevine yellows is caused by a genetically distinct phytoplasma species separate from other grapevine yellows pathogens reported in Europe and elsewhere.
Key findings
- A novel phytoplasma designated "Candidatus Phytoplasma australiense" was detected in all naturally diseased Australian grapevines but not in healthy plants
- The pathogen represents a new subgroup (16SrI-J) within phytoplasma group 16SrI based on unique RFLP patterns of 16S rDNA
- Phylogenetic analysis placed the Australian phytoplasma in a distinct subclade (xii) most closely related to, but clearly separate from, stolbur phytoplasma
- The organism contains unique 16S rRNA sequences that distinguish it from all previously described phytoplasmas, including signatures at positions 191-215 and 999-1013
- Species-specific PCR primers were developed enabling direct detection of this pathogen from diseased grapevine tissue
This summary was generated automatically from the article PDF and is not part of the original publication. Refer to the PDF for the authoritative text.
Abstract
A phytoplasma was detected in naturally diseased Chardonnay grapevines exhibiting symptoms of Australian grapevine yellows disease. The use of PCR designed to amplify phytoplasma DNA resulted in detection of phytoplasma DNA in all of the diseased plants examined; no phytoplasma DNA was detected in healthy seedling grapevines. The collective restriction fragment length polymorphism (RFLP) patterns of amplified 16S ribosomal DNA differed from the patterns described previously for other phytoplasmas. On the basis of the RFLP patterns, Australian grapevine yellows phytoplasma was classified as a representative of a new subgroup, designated subgroup 16SrI-J, in phytoplasma 16S rRNA group 16SrI (aster yellows and related phytoplasmas). A phylogenetic analysis in which parsimony of 16S rRNA gene sequences from this and other group 16SrI phytoplasmas was used identified the Australian grapevine yellows phytoplasma as a member of a distinct subclade (subclade xii) in the phytoplasma clade of the class Mollicutes. A phylogenetic tree constructed on the basis of 16S rRNA gene sequences was consistent with the hypothesis that there was divergent evolution of Australian grapevine yellows phytoplasma and its closet known relative, European stolbur phytoplasma (subgroup 16SrI-G), from a common ancestor. The unique properties of the DNA from the Australian grapevine yellows phytoplasma clearly establish that it represents a new taxon, "Candidatus Phytoplasma australiense."