Location: Molecular Plant Pathology LaboratoryTitle: 'Candidatus phytoplasma solani’, a novel taxon associated with stolbur and bois noir related diseases of plants) Author
Submitted to: International Journal of Systematic and Evolutionary Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/11/2013
Publication Date: 7/11/2013
Citation: Quaglino, F., Zhao, Y., Casati, P., Bulgari, D., Bianco, P., Wei, W., Davis, R.E. 2013. 'Candidatus phytoplasma solani’, a novel taxon associated with stolbur and bois noir related diseases of plants. International Journal of Systematic and Evolutionary Microbiology. 63:2879-2894. Interpretive Summary: Bois noir is one of the most damaging diseases known in cultivated grapevines; stolbur is one of the most serious diseases of vegetable crops and other plants. Both diseases are attributed to infection by strains of a phytoplasma, a tiny bacterium that has no cell wall, that is spread by sap-sucking insects, and cannot be isolated like other bacteria and grown in the laboratory. There is need to obtain precise molecular markers for identification and classification of the bois noir/stolbur phytoplasma to aid the design of appropriate disease control measures and to enable quarantine measures that effectively prevent spread of the disease. Using molecular methods to study specific genes, we found that the phytoplasma represents a previously undescribed species level lineage, for which we have proposed the designation, ‘Candidatus Phytoplasma solani’. Our results provide molecular markers by which the ‘Ca. Phytoplasma solani’ may be detected and identified, benefitting measures to control the disease, as well as aiding implementation of quarantine measures to prevent its spread. Such progress will aid the cause of food security and sustainable agricultural production. This report will be of interest to diagnostics laboratories, research scientists, farmers, and quarantine agencies internationally.
Technical Abstract: Phytoplasmas classified in group 16SrXII infect a wide range of plants and are transmitted by polyphagous planthoppers of the family Cixiidae. Based on 16S rRNA gene sequence identity and biological properties, group 16SrXII encompasses several species, including ‘Candidatus Phytoplasma australiense’, ‘Ca. Phytoplasma japonicum’, and ‘Ca. Phytoplasma fragariae’. Other group 16SrXII phytoplasma strains are associated with stolbur disease in wild and cultivated herbaceous and woody plants and with bois noir disease in grapevines (Vitis vinifera L.). Such latter strains have been informally proposed to represent a separate species, ‘Candidatus Phytoplasma solani’, but a formal description of this taxon has not previously been published. In the present work, stolbur disease strain STOL11 was distinguished from reference strains of previously described ‘Ca. Phytoplasma’ species based on 16S rRNA gene sequence (16S rDNA) similarity and a unique signature sequence in 16S rDNA. Other stolbur and bois noir associated (‘Ca. Phytoplasma solani’) strains shared >99% 16S rDNA sequence similarity with strain STOL11 and contained the signature sequence. ‘Ca. Phytoplasma solani’ is the only phytoplasma known to be transmitted by Hyalesthes obsoletus. Insect vectorship and molecular characteristics are consistent with the concept that diverse ‘Ca. Phytoplasma solani’ strains share common properties and represent an ecologically distinct gene pool. Phylogenetic analyses of 16S rRNA, tuf, secY, and rplV-rpsC gene sequences supported this view and yielded congruent trees on which ‘Ca. Phytoplasma solani’ strains formed, within the group 16SrXII clade, a monophyletic subclade that was most closely related to, but distinct from, that of ‘Ca. Phytoplasma australiense’-related strains. Based on distinct molecular and biological properties, stolbur and bois noir associated strains are proposed to represent a novel species level taxon, ‘Ca. Phytoplasma solani’; STOL11 is designated the reference strain.