First report of a new grapevine yellows disease in Peru and its association with infection by a ‘Candidatus Phytoplasma brasiliense’-related phytoplasma strain

Authors: Wei, Wei; PEREZ-LOPEZ, EDEL - Auburn University; BERMUDEZ-DIAZ, LUDISLEYDIS - Universidad Privada Atenor Orrego; Davis, Robert; GRANDA-WONG, CARLOS - Universidad Nacional De Piura; Zhao, Yan

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/31/2016
Publication Date: 3/1/2017
Citation: Wei, W., Perez-Lopez, E., Bermudez-Diaz, L., Davis, R.E., Granda-Wong, C., Zhao, Y. 2017. First report of a new grapevine yellows disease in Peru and its association with infection by a ‘Candidatus Phytoplasma brasiliense’-related phytoplasma strain. Plant Disease. 101:502. doi: 10.1094/PDIS-08-16-1152-PDN.

Interpretive Summary: Cultivated grapevine plants are susceptible to infection by phytoplasmas, a unique group of bacteria that lack a cell wall. Phytoplasmas invade nutrition-conducting vessels of grapevine plants, causing several diseases collectively called grapevine yellows (GY). The GY diseases around the globe exhibit very similar symptoms but are attributed to infection by different species of phytoplasmas. Correct identification of the GY phytoplasma species is crucial for understanding disease epidemiology and for devising effective control measures, as different species of phytoplasmas may be spread by different insect vectors. In the fall of 2015, grapevine plants exhibiting symptoms indicative of a possible GY disease were observed in a vineyard located in northwestern Peru. DNA finger printing analysis of phytoplasma-unique genetic markers confirmed that phytoplasma infection did occur in the vineyard. This is the first documented case of a GY disease in Peru. Further genotyping of the phytoplasma revealed that the Peru GY disease agent is closely related to the reference strain of ‘Ca. Phytoplasma brasiliense’, a species that was previously not found in Peru and never implicated in a GY disease anywhere in the world. Results from the present study indicate that this phytoplasma species has spread to a new geographic region, and its host range has extended to an important horticultural crop, signaling an urgent need for comprehensive measures to control the pathogen and minimize its impact on agriculture and natural ecosystems. The research team also identified molecular markers for specific detection of the Peru GY phytoplasma. The information is important to the viticulture industry and extension personnel for GY disease diagnosis and management and is critical to regulatory agencies for preventing exotic pathogens from being introduced into the U.S.

Technical Abstract: Grapevine (Vitis vinifera L.), key source for wine production, is one of the most valuable horticultural crops in the world. Native to the Mediterranean region, V. vinifera is now cultivated on every continent and covers nearly eight million hectares of land. However, the health of this cultivated grapevine continues to be threatened by several diseases collectively referred as grapevine yellows (GY). Typical symptoms of GY include downward rolling of leaves, yellowing or necrosis of leave veins, uneven lignification of stems, and shriveling of grape clusters; in sensitive cultivars, GY can cause premature plant death. All types of GY studied thus far are attributed to infection by phloem-inhabiting, insect-transmitted cell wall-less bacteria known as phytoplasmas, although the species of phytoplasma involved in an individual GY differs. In the fall of 2015, grapevine plants exhibiting symptoms of leaf discoloration, veinal necrosis, and in some cases fruit shriveling, were observed in a vineyard located in Piura, northwestern Peru. Since the symptoms were indicative of possible GY, molecular diagnostics for phytoplasmal infection was deployed. Total DNA was extracted from leaf samples of five symptomatic plants and served as templates in polymerase chain reactions (PCRs) primed by phytoplasma universal primer pair P1A/16S-SR. An amplicon of 1.5 kb was obtained from DNA samples of the three symptomatic plants exhibiting fruit shriveling. In parallel diagnostic assays, nested PCRs were performed using primer pair P1/P7 followed by R16F2n/R16R2. A 1.25 kb genome segment was amplified from DNA samples of the same three symptomatic plants. The amplicons were cloned and nucleotide sequences determined. The DNA sequence data showed that the 1.5 kb amplicon contained a near-full length 16S rRNA gene (16S rDNA) and the 1.2 kb amplicon encompassed the full F2nR2 segment of the 16S rDNA. All six 16S rDNA sequences derived by the two PCR methods from the three independent samples are mutually identical in common regions and possess a conserved block that is characteristic of ‘Candidatus Phytoplasma’ species, confirming that phytoplasmal infection occurred in the vineyard. To our knowledge, this is the first report of a phytoplasmal GY disease in Peru. The phytoplasma is hereby designated as PeruGY1. The 16S rDNA sequences of the three PeruGY1 strains were deposited in the GenBank. An iPhyClassifier operation, using the 16S rDNA sequences of three PeruGY1 strains as queries, revealed that PeruGY1 is closely related to the reference strain of ‘Ca. Phytoplasma brasiliense’. This is the first time ‘Ca. Phytoplasma brasiliense’ is implicated in a GY disease. ‘Ca. Phytoplasma brasiliense’ was originally discovered from diseased hibiscus plants in Brazil, and, in the Americas, related strains have been reported only in Costa Rica and Brazil. Results from our present study indicate that the phytoplasma has spread to a new geographic region, and its host range has extended to an important horticultural crop, signaling an urgent need for comprehensive measures to control the pathogen and minimize its impact on agriculture and natural ecosystems.