The agent associated with blue dwarf disease in wheat represents a new phytoplasma taxon, 'Candidatus Phytoplasma tritici'

Authors: Zhao, Yan; Wei, Wei; DAVIS, ROBERT - Former ARS Employee; LEE, ING-MING - Former ARS Employee; Bottner, Kristi

Submitted to: International Journal of Systematic and Evolutionary Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/1/2020
Publication Date: 1/19/2021
Citation: Zhao, Y., Wei, W., Davis, R.E., Lee, I., Bottner-Parker, K.D. 2021. The agent associated with blue dwarf disease in wheat represents a new phytoplasma taxon, 'Candidatus Phytoplasma tritici'. International Journal of Systematic and Evolutionary Microbiology. 71:(1). https://doi.org/10.1099/ijsem.0.004604.
DOI: https://doi.org/10.1099/ijsem.0.004604

Interpretive Summary: Wheat blue dwarf (WBD) is one of the most economically damaging cereal crop diseases in northwestern China. The causal agent of the disease is a small bacterium known as phytoplasma. The WBD phytoplasma is capable of invading nutrient-conducting vessels of affected wheat plants, causing stunted growth, bluish leaf discoloration, floral deformation, and sterility. Prior to the present study, the WBD phytoplasma was considered belonging to a species termed 'Candidatus Phytoplasma asteris'. In the present study, ARS scientists found that the WBD phytoplasma has its unique transmitting vector and is able to elicit a distinctive symptom in wheat. In addition, the WBD phytoplasma possesses molecular and genomic characteristics that are significantly different from those of any previously established phytoplasma species. Such distinguishing ecological, molecular, and genomic features justify the recognition of the WBD phytoplasma as a novel taxon. The ARS scientists named the new taxon 'Candidatus Phytoplasma tritici'. The ARS research team also identified molecular markers that can be used to detect and identify this new phytoplasma species. This report will be of interest to research scientists, plant disease diagnosticians, and extension personnel who are concerned with genetic diversity of bacterial pathogens and plant disease management. This information is also important to regulatory agencies for implementing new quarantine measures to prevent spread of the pathogen.

Technical Abstract: Wheat blue dwarf (WBD) is one of the most economically damaging cereal crop diseases in northwestern China. The causative agent of the WBD disease is a phytoplasma affiliated with the aster yellows (AY) group, subgroup C (16SrI-C). Since phytoplasma strains within the AY group are ecologically and genetically diverse, it has been conceived that the AY phytoplasma group may consist of more than one species. This communication presents evidence to demonstrate that, while each of the two 16 rRNA genes of the WBD phytoplasma shares >97.5% sequence similarity with that of 'Candidatus Phytoplasma asteris' reference strain, the WBD phytoplasma clearly represents an ecologically separated lineage: the WBD phytoplasma not only has its unique transmitting vector (Psammotettix striatus) but also elicits a distinctive symptom in its predominant plant host (wheat). In addition, the WBD phytoplasma possesses molecular characteristics that further manifest its significant divergence from 'Ca. Phytoplasma asteris'. Such molecular characteristics include lineage-specific antigenic membrane proteins and a lower than 95% genome-wide average nucleotide identity score with 'Ca. Phytoplasma asteris'. These ecological, molecular, and genomic evidences justify the recognition of the WBD phytoplasma as a novel taxon, 'Candidatus Phytoplasma tritici'.