Unraveling the etiology of North American grapevine yellows (NAGY): multilocus genotyping and structural analysis of secY proteins distinguish NAGYIII phytoplasma strains from strains causing X-disease

Authors: Davis, Robert; Dally, Ellen; Zhao, Yan; Lee, Ing Ming; Wei, Wei; WOLF, TONY - Virginia Tech; BEANLAND, LEANN - Virginia Tech; LEDOUX, DOUGLAS - Missouri Department Of Conservation; JOHNSON, DAVID - Missouri Department Of Conservation; FIOLA, JOSEPH - Western Maryland Research And Education Center; WALTER-PETERSON, HANS - Cornell University; DAMI, IMED - Ohio Agricultural Research & Development Center; CHIEN, MARK - Pennsylvania Department Of Agriculture

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/29/2015
Publication Date: 8/13/2015
Publication URL: http://handle.nal.usda.gov/10113/5425112
Citation: Davis, R.E., Dally, E.L., Zhao, Y., Lee, I., Wei, W., Wolf, T.K., Beanland, L., Ledoux, D.G., Johnson, D.A., Fiola, J.A., Walter-Peterson, H., Dami, I., Chien, M. 2015. Unraveling the etiology of North American grapevine yellows (NAGY): multilocus genotyping and structural analysis of secY proteins distinguish NAGYIII phytoplasma strains from strains causing X-disease. Phytopathology. 99:1087-1097. doi.org/10.1094/PDIS-11-14-1185-RE.

Interpretive Summary: The term, grapevine yellows (GY), refers to any of several diseases of cultivated grapevine that are attributed to plant infection by different species of bacteria known as phytoplasmas (formerly mycoplasmalike organisms, MLOs). The GY diseases around the world exhibit virtually indistinguishable symptoms but are associated with plant infection by diverse species of phytoplasmas that differ in their spread by specific insect vectors, plant host ranges, and natural ecologies. Since it is difficult, if not impossible, to distinguish different GY diseases from one another based on symptoms alone, genotyping of GY phytoplasmas is critically important for understanding disease etiology and epidemiology and for devising effective management strategies. The present study of GY in eastern U.S. was prompted by a resurgence of the disease (now termed North American grapevine yellows, NAGY) during 2009-2011 in Virginia. In this communication, we present definitive identification and characterization of NAGY phytoplasmas in Virginia and New York State and report discovery of NAGY in Maryland, Pennsylvania, Ohio, and Missouri. The distribution of NAGY across six states suggests that the disease may occur over a much wider area of the U.S. We further present evidence of NAGY in wine grape cultivars including Chardonnay, Pinot gris (Pinot grigio), Viognier, Petit Manseng, Cabernet Sauvignon, Malbec, Merlot, Black Malvasia (Malvasia nera), Syrah, Pinot noir, and Cabernet franc. Results from detailed analyses of multiple phytoplasma genes and results from structural analysis of an essential phytoplasma protein yielded molecular genetic markers that clearly distinguished grapevine-infecting phytoplasmas from other phytoplasmas, including closely related strains causing Prunus X-disease. Correct diagnosis of a grapevine yellows diseases worldwide requires precise phytoplasma identification for accurate assignment of disease etiology and effective applications of disease control measures. The markers thus should prove useful in research to understand NAGY epidemiology and in efforts to devise strategies for improved disease management.

Technical Abstract: North American grapevine yellows (NAGY) disease has sometimes been ascribed to infection of Vitis vinifera L. by X-disease phytoplasma, but the accuracy of this attribution has remained open to question. In the present study of NAGY etiology, the disease was discovered in Maryland, Pennsylvania, Ohio, and Missouri; occurrence of NAGY in New York State was definitively documented; and presence of NAGY in Virginia was reaffirmed. Characterization of the NAGY phytoplasma strains by multilocus genotyping pointed to NAGY as a disease complex caused by no less than two different phytoplasma species. Some (NAGYI) phytoplasmas were strains that fit within the description of ‘Ca. Phytoplasma asteris’, while most (NAGYIII strains) were related to Prunus X-disease phytoplasma). Analysis of 16S rRNA genes revealed that all NAGYIII strains were variants (16SrIII-A*) of X-disease phytoplasma subgroup 16SrIII-A. Single nucleotide polymorphisms (SNPs) in 16S rRNA, secY, and ribosomal protein (rp) genes distinguished two NAGYIII lineages, a and ß. The same lineages were distinguished by structural analysis of SecY proteins; deduced 3-dimensional structure differed in putatively membrane surface-exposed regions of the proteins. The findings were consistent with the concept that Prunus X-disease and grapevine NAGYIII disease are caused by different phytoplasma strains.