Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/10/2018
Publication Date: 9/1/2018
Citation: Davis, R.E., Dally, E.L., Zhao, Y., Wolf, T.K. 2018. Genotyping points to divergent evolution of ‘Candidatus Phytoplasma asteris’ strains causing North American grapevine yellows and strains causing aster yellows. Plant Disease. 102:1696-1702. https://doi.org/10.1094/PDIS-10-17-1690-RE.
Interpretive Summary: Phytoplasmas are minute, specialized bacteria causing plant diseases that result in economic losses worldwide. They are spread by insects that feed in the food conducting tissues in veins, where the phytoplasmas live and induce disease symptoms including development of abnormally small leaves. To reduce the spread of phytoplasmas, it is important to know the identity of phytoplasma(s) infecting diverse plant species, including important commercial crops. In this work, we investigated a disease of cultivated grapevine (Vitis vinifera) plants. Because different phytoplasma species cause mutually indistinguishable disease symptoms in V. vinifera, identification of the causal phytoplasma is critically important for correctly diagnosing the grapevine disease and for devising and applying appropriately targeted disease management measures. We analyzed the DNA of diseased cultivated grapevine plants and determined that the plants were infected by a phytoplasma that is related to the phytoplasma that causes the well known aster yellows disease in herbaceous plants, but the grapevine phytoplasma was different. This grapevine phytoplasma appears to be evolving in a direction that is increasingly distinguishing it from other phytoplasmas, including aster yellows phytoplasma. Our new information expands knowledge of plant diseases that can be caused by phytoplasmas, and it provides molecular markers useful for detecting and identifying the phytoplasma, identifying its insect vector, and preventing its spread.
Technical Abstract: Grapevine yellows diseases occur in cultivated grapevine (Vitis vinifera L.) on several continents, where the diseases are known by different names depending upon the identities of the causal phytoplasmas. In this study, phytoplasma strains associated with grapevine yellows disease (North American grapevine yellows, NAGY) in vineyards of Pennsylvania were characterized as belonging to 16S rRNA gene RFLP group 16SrI (aster yellows phytoplasma group), subgroup I-B (I-B) and variant subgroup I-B*. The strains (NAGYI strains) were subjected to genotyping based on analyses of 16S rRNA and secY genes, and to in silico 3-dimensional modeling of the SecY protein. Although the NAGYI strains are closely related to aster yellows (AY) phytoplasma strains and are classified like AY strains in subgroup I-B or in variant subgroup I-B*, the results from genotyping and protein modeling could signal ongoing evolutionary divergence of NAGYI strains from related strains in subgroup 16SrI-B.