Location: Molecular Plant Pathology LaboratoryTitle: First report of North American grapevine yellows (NAGY) in Kansas: Association of ‘Candidatus Phytoplasma pruni’- and ‘Ca. Phytoplasma asteris’-related strains with the disease
|DALLY, ELLEN - Retired ARS Employee
|WEBB, CRAIG - Kansas State University
|APPEL, JON - Kansas Department Of Agriculture
Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/27/2018
Publication Date: 2/11/2019
Citation: Davis, R.E., Dally, E.L., Zhao, Y., Webb, C., Appel, J.A. 2019. First report of North American grapevine yellows (NAGY) in Kansas: Association of ‘Candidatus Phytoplasma pruni’- and ‘Ca. Phytoplasma asteris’-related strains with the disease. Plant Disease. https://doi.org/10.1094/PDIS-05-18-0869-PDN.
Interpretive Summary: Phytoplasmas are small bacteria that cause diseases in economically important crops worldwide. In this work, we discovered that some cultivated grapevines (Vitis vinifera L.) in the state of Kansas are affected by a disease known as North American grapevine yellows (NAGY), a disease caused by phytoplasma. It was critically important to determine whether the phytoplasma in Kansas grapevines could be an exotic phytoplasma known to cause serious disease of grapevines in Europe or other regions. We therefore analyzed the DNA of diseased Kansas grapevine plants and determined that the diseased plants were infected by two different phytoplasmas. The findings provide the first evidence of NAGY disease in the state of Kansas, while revealing that the two NAGY phytoplasma lineages in Kansas grapevines are closely related to NAGY phytoplasma strains previously reported in other states. This work provides molecular markers useful for detecting and identifying the phytoplasmas and their insect vectors, information needed for preventing their spread. While expanding the known geographic range of NAGY disease, this new knowledge also points to the possibility that the geographic extent of NAGY is greater than currently realized.
Technical Abstract: Plants of cultivated grapevine (Vitis vinifera L.) exhibiting symptoms suggestive of grapevine yellows (GY) disease were observed in vineyards in Kansas during 2013 and 2014. Symptoms consisted of leaf yellowing, downward rolling of leaf margins, and shriveling of fruit clusters. Symptomatic plants of cultivars Riesling (designated KS-JO48) and Chardonnay (designated KS-DG12) were selected for further work. To detect and identify the suspected phytoplasmal pathogen strain(s), DNA was extracted from veins excised from symptomatic leaves and used as template in polymerase chain reactions (PCRs) for amplification of phytoplasmal rRNA gene (rDNA) and secY gene sequences as previously described. Nucleotide sequences of the PCR products were determined and deposited in the GenBank database under accession numbers MH085064 and MH085065 (for cloned rrnA and rrnB sequences, respectively reflecting interoperon heterogeneity) and MG992477 (secY) for KS-JO48; and MH085066 (rrnA), MH085067 (rrnB), and MG992478 (secY) for KS-DG12. In silico analysis of 16S rRNA gene sequences, using iPhyClassifier, revealed that plant KS-JO48 was infected by a ‘Candidatus Phytoplasma asteris’-related phytoplasma belonging to subgroup 16SrI-A (I-A), and that plant KS-DG12 was infected by a ‘Candidatus Phytoplasma pruni’-related phytoplasma belonging to subgroup variant 16SrIII-A* (III-A*). Nucleotide sequence alignment of the strain KS-DG12 16S rRNA gene sequence with those of North American grapevine yellows (NAGY) strains previously reported revealed that strain KS-DG12 is a NAGYIIIß sequevar corresponding to sequevar NAGYIIIß strains found in Maryland, Virginia, New York, and Pennsylvania. Alignments and phylogenetic analyses of secY gene sequences confirmed the close relatedness of the Kansas subgroup I-A strain KS-JO48 and subgroup III-A* (NAGYIIIß sequevar) strain KS-DG12 phytoplasmas with the reference strains of ‘Candidatus Phytoplasma asteris’ and ‘Candidatus Phytoplasma pruni’, respectively. The results provide the first evidence of NAGY in the state of Kansas, while revealing that the two NAGY phytoplasma strain lineages reported here are closely related to NAGY phytoplasma strains in other states. Although further work will be necessary to assess the impacts of NAGY in Kansas, the findings reported here expand the known geographic range of NAGY disease and support the concept that the geographic extent of NAGY is greater than currently realized.