Submitted to: International Journal of Systematic and Evolutionary Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/24/2003
Publication Date: 7/1/2004
Citation: Lee, I., Gundersen, D.E., Davis, R.E., Bottner, K.D., Marcone, C., Seemuller, E. 2004. 'Candidatus Phytoplasma asteris', a new phytoplasma taxon associated with aster yellows and related diseases. International Journal of Systematic and Evolutionary Microbiology. 54:1037-1048. Interpretive Summary: Phytoplasmas are unusual bacteria that lack a cell wall and that cause several hundred economically important diseases in plants worldwide. A phytoplasma causing severe yellows disease (aster yellows, AY) in China aster is termed aster yellows phytoplasma. This and related phytoplasmas form a large and diverse group of bacteria that cause more than 100 diseases in diverse plant species including ornamental, vegetable, grain, fruit, and forest crops. The many phytoplasmas belonging to this group are difficult to distinguish from one another. By combined analysis of two genes involved in protein synthesis, we have found that the AY phytoplasma group represents at least one phytoplasma species. This paper reports the relatedness among the aster yellows phytoplasmas, and describes a new species, 'Candidatus Phytoplasma asteris' to include all members of the aster yellows phytoplasma group. The information in this paper will aid implementation of quarantine regulations internationally, and it will help extension workers and plant diagnosticians to determine how to combat the diseases caused by the aster yellows group phytoplasmas.
Technical Abstract: Aster yellows (AY) group (16SrI) phytoplasmas are associated with more than 100 economically important diseases worldwide and represent the most diverse and widespread phytoplasma group. Based on phylogenetic analysis of 16S rDNA sequences from diverse strains in the AY phytoplasma group and other phytoplasmas, the AY group members form a discrete subclade within the phytoplasma clade, most closely related to the stolbur phytoplasma subclade. Among the subclades within the phytoplasma clade, members of the AY subclade are more closely related than any other phytoplasmas to their close culturable relatives, namely Acholeplasma spp., A. palmae and A. modicum, members of the Anaeroplasma clade. Within the AY subclade, six distinct phylogenetic lineages were revealed. Congruent phylogenies obtained by phylogenetic analysis of tuf gene and ribosomal protein (rp) operon gene sequences further resolved the diversity among AY group phytoplasmas. The distinct phylogenetic lineages can be readily identified through restriction fragment length polymorphism (RFLP) analysis of 16SrRNA, tuf, or rp gene sequences. Ten subgroups were differentiated among the AY group phytoplasmas based on RFLP analysis of rp gene sequences. We propose that AY group phytoplasmas represent at least one new taxon. The AY phytoplasma belonging to subgroups16SrI-B, rpI-B, tufI-B was selected to represent the AY group as new taxon, 'Candidatus Phytoplasma asteris'. The 'Candidatus Phytoplasma asteris' reference strain is OAY, the phytoplasma associated with evening primrose (Oenothera hookeri) virescence in Michigan. We also present a comprehensive database of diverse AY phytoplasma strains and their geographic distribution.