Monitoring the Spread of Grapevine Viruses in Vineyards of Contrasting Agronomic Practices: A Metagenomic Investigation.

This study investigated the transmission of grapevine viruses, specifically grapevine red blotch virus (GRBV) and grapevine Pinot gris virus (GPGV), in vineyards in Niagara Region, Ontario, Canada. Forty sentinel vines that were confirmed free of GRBV and GPGV by both high-throughput sequencing (HTS) and endpoint polymerase chain reaction (PCR) were introduced to two vineyards (one organic and one conventional) that were heavily infected with both GRBV and GPGV. Four months post-introduction, the sentinel vines were relocated to a phytotron. The HTS results from 15 months post-introduction revealed a widespread infection of GPGV among the sentinel vines but did not detect any GRBV. The GPGV infection rate of sentinel vines in the organic vineyard (13/18) was higher than in the conventional vineyard (1/19). The possibility of an alternative viral reservoir was assessed by testing the most abundant plants in between rows (Medicago sativa, Trifolium repens, Cirsium arvense and Taraxacum officinale), perennial plants in border areas (Fraxinus americana, Ulmus americana, Rhamnus cathartica) and wild grape (unknown Vitis sp.). The HTS result showed that cover crops and perennial plants did not harbor any grapevine viruses, while 4/5 wild grapes tested positive for GPGV but not GRBV. A pairwise sequence identity analysis revealed high similarities between the GPGV isolates found in the established vines on the vineyard and the newly contracted GPGV isolates in the sentinel vines, implicating a recent transmission event. This work provides novel insights into the spread of grapevine viruses in Niagara Region and is also the first direct proof of the spread of GPGV in natural vineyard conditions in North America.

Phylogenetic and Evolutionary Studies of Grapevine Pinot Gris Virus Isolates from Canada.

This study investigated the phylogenetic relationship of grapevine Pinot gris virus (GPGV) isolates from Canada with GPGV isolates reported worldwide. Full-length genomes of 25 GPGV isolates representing the main four grape-growing regions in Canada (British Columbia, Ontario, Nova Scotia and Quebec) were sequenced and compared to genomes of 43 GPGV isolates representing eight countries and three continents. Phylogenetic analysis based on full genome sequences revealed an unambiguous separation of North American GPGV isolates with isolates from Europe and Asia. Within the North American clade, GPGV isolates from the USA segregated into a distinct subclade, whereas the relationships amongst GPGV isolates from different regions of Canada were not clearly defined. The phylogenetic analysis of the overlapping regions of MP and CP genes involving 169 isolates from 14 countries resulted in two distinctive clades, which were seemingly independent of their country of origin. Clade 1 included the majority of asymptomatic isolates (81% asymptomatic), whereas clade 2 was predominantly formed of symptomatic isolates (78% symptomatic). This research is the first study focused on the genetic variability and origin of GPGV in Canada.

Naked-Eye Detection of Grapevine Red-Blotch Viral Infection Using a Plasmonic CRISPR Cas12a Assay.

Herein, we described a novel plasmonic CRISPR Cas12a assay for the visual, colorimetric detection of grapevine viral infections. Our assay generates rapid and specific colorimetric signals for nucleic acid amplicons by combining the unique target-induced incriminate single-stranded DNase activity of Cas12a with plasmon coupling of DNA functionalized gold nanoparticles. The practical applicability of our plasmonic assay was successfully demonstrated through the detection of emerging red-blotch viral infections in grapevine samples collected from commercial vineyards.

SYBR(®) Green-based real-time quantitative reverse-transcription PCR for detection and discrimination of grapevine viruses.

A SYBR(®) Green-based real-time quantitative reverse transcription PCR (qRT-PCR) assay in combination with melt-curve analysis (MCA) was optimized for the detection of nine grapevine viruses. The detection limits for simplex qRT-PCR for all nine grapevine viruses were estimated to be in the range of 214-1112 copies of the virus genome. Amplicons with melting temperatures (Tm) separated by at least 2°C in the MCA could differentiate two viruses in the same reaction. Therefore, eight of the nine viruses could be co-diagnosed in five different combinations of duplex assays. Of 305 grape leaf samples from the field or greenhouse, 162 were positive for at least one of the nine grapevine viruses using the duplex qRT-PCR assays. In contrast, only 127 samples were positive using endpoint RT-PCR and PCR assays, indicating the enhanced sensitivity of duplex real-time PCR. In addition, the duplex qRT-PCR assays were be used to detect Grapevine leafroll associated virus 3 (GLRaV-3) in its vector, the grape mealybug (Pseudococcus maritimus Ehrhorn), and Grapevine red blotch-associated virus (GRBaV) in Virginia creeper leafhopper (Erythroneura ziczac Walsh). The simplex and duplex real-time PCR assays developed in this study can be used to examine transmission of co-occruing viruses by insect vectors as well as for rapid and sensitive detection of viruses in infected grapevines.

Molecular characterization and impacts of a strain of Grapevine leafroll-associated virus 2 causing asymptomatic infection in a wine grape cultivar.

BACKGROUND: Grapevine leafroll (GLD) is considered as the most economically important virus disease affecting wine grapes (Vitis vinifera L.) in many grapevine-growing regions. GLD produces distinct symptoms in red- and white-berried cultivars. In this study, we determined the complete genome sequence of an asymptomatic strain of Grapevine leafroll-associated virus 2 (GLRaV-2) and studied its impacts on fruit yield and berry quality attributes in an own-rooted, red-berried wine grape cultivar. FINDINGS: The complete genome of GLRaV-2 obtained from a red-berried wine grape cultivar Sangiovese, designated as GLRaV-2-SG, was determined to be 16,474 nucleotides in length. In pairwise comparisons, using complete genome sequences of GLRaV-2 strains available in GenBank, GLRaV-2-SG was more closely related to GLRaV-2-OR1 from Oregon, USA, and GLRaV-2-93/955 from South Africa, and distantly related to GLRaV-2-BD from Italy and GLRaV-2-RG from USA. Fruit yield estimates and berry quality analysis at the time of commercial harvest indicated that GLRaV-2-SG had little impact on fruit yield and total soluble solids, juice pH and total anthocyanins of berry skin. CONCLUSIONS: Because so little is known about the effects of asymptomatic virus infections in wine grapes, this study expanded our knowledge of the occurrence and impacts of GLRaV-2 causing asymptomatic infections. Our results indicated that an asymptomatic strain of GLRaV-2 may not cause significant effects to overall fruit yield and berry quality in own-rooted vines, but can affect its host in more subtle ways. Since disease symptoms are not apparent, relying on visual symptoms during disease surveys may result in the escape of asymptomatic strains of GLRaV-2. Thus, it is necessary to use appropriate diagnostic assays for reliable detection of viruses causing asymptomatic infections.

A leafhopper-transmissible DNA virus with novel evolutionary lineage in the family geminiviridae implicated in grapevine redleaf disease by next-generation sequencing.

A graft-transmissible disease displaying red veins, red blotches and total reddening of leaves in red-berried wine grape (Vitis vinifera L.) cultivars was observed in commercial vineyards. Next-generation sequencing technology was used to identify etiological agent(s) associated with this emerging disease, designated as grapevine redleaf disease (GRD). High quality RNA extracted from leaves of grape cultivars Merlot and Cabernet Franc with and without GRD symptoms was used to prepare cDNA libraries. Assembly of highly informative sequence reads generated from Illumina sequencing of cDNA libraries, followed by bioinformatic analyses of sequence contigs resulted in specific identification of taxonomically disparate viruses and viroids in samples with and without GRD symptoms. A single-stranded DNA virus, tentatively named Grapevine redleaf-associated virus (GRLaV), and Grapevine fanleaf virus were detected only in grapevines showing GRD symptoms. In contrast, Grapevine rupestris stem pitting-associated virus, Hop stunt viroid, Grapevine yellow speckle viroid 1, Citrus exocortis viroid and Citrus exocortis Yucatan viroid were present in both symptomatic and non-symptomatic grapevines. GRLaV was transmitted by the Virginia creeper leafhopper (Erythroneura ziczac Walsh) from grapevine-to-grapevine under greenhouse conditions. Molecular and phylogenetic analyses indicated that GRLaV, almost identical to recently reported Grapevine Cabernet Franc-associated virus from New York and Grapevine red blotch-associated virus from California, represents an evolutionarily distinct lineage in the family Geminiviridae with genome characteristics distinct from other leafhopper-transmitted geminiviruses. GRD significantly reduced fruit yield and affected berry quality parameters demonstrating negative impacts of the disease. Higher quantities of carbohydrates were present in symptomatic leaves suggesting their possible role in the expression of redleaf symptoms.

Complete genome sequence analysis of an American isolate of Grapevine virus E.

The complete genome sequence of Grapevine virus E (GVE) collected from a red-berried wine grape cultivar (Cabernet Sauvignon) in Washington State was determined. The 7,568 nucleotide long genome of GVE is more similar in sequence identity with a GVE isolate from a wine grape cv. Shiraz from South Africa when compared with an isolate from "Aki Queen" grape from Japan. Like GVE isolates from South Africa and Japan, the Washington isolate encodes five open reading frames (ORFs) and the overall genome organization is identical among these isolates. In addition to AlkB domain, a DExD domain, belonging to the DEAD-like helicases superfamily, was present upstream of the helicase domain in the replicase ORF of the virus.

Grapevine leafroll-associated virus 1 occurs as genetically diverse populations.

The genetic diversity of 34 isolates of Grapevine leafroll-associated virus 1 (GLRaV-1) from different wine, table, and ornamental grape cultivars in California, New York, and Washington States in the United States was investigated. Segments of the heat-shock protein 70 homolog (HSP70h) gene, coat protein (CP) gene, coat protein duplicate 2 (CPd2) gene, and open reading frame 9 (p24) were amplified by reverse-transcription polymerase chain reaction, cloned, and sequenced. A pairwise comparison of nucleotide sequences revealed intra- and interisolate sequence diversity, with CPd2 and HSP70h being the most and the least divergent, respectively, among the four genomic regions studied. The normalized values for the ratio of nonsynonymous substitutions per nonsynonymous site to synonymous substitutions per synonymous site indicated different purifying selection pressures acting on each of the four genomic regions, with the CP and CPd2 being subjected to the strongest and weakest functional constraints, respectively. A global phylogenetic analysis of sequences from the four genomic regions revealed segregation of GLRaV-1 isolates into three major clades and a lack of clearly defined clustering by geographical origin. In contrast, only two lineages were apparent when the CP and CPd2 gene sequences were used in phylogenetic analyses. Putative recombination events were revealed among the HSP70h, CP, and p24 sequences. The genetic landscape of GLRaV-1 populations presented in this study provides a foundation for better understanding of the epidemiology of grapevine leafroll disease across grape-growing regions in the United States. In addition, this study will benefit grape clean plant programs across the country in improving the sanitary status of planting materials provided to nurseries and grape growers.

Importance and genetic diversity of vegetable-infecting tospoviruses in India.

A survey for Peanut bud necrosis virus (PBNV), Watermelon bud necrosis virus (WBNV), Capsicum chlorosis virus (CaCV), and Iris yellow spot virus (IYSV) was conducted between 2002 and 2009 in the major vegetable-growing areas in India. PBNV was documented widely in tomato and chili peppers in 14 states representing southern, north-western, north-eastern, and central regions and WBNV was predominantly detected in watermelons and cucurbits in all except north-eastern regions. In addition, the expanded host range of PBNV to watermelons and other cucurbits and WBNV to tomato and chili peppers was observed leading to natural mixed infection of the two viruses. IYSV was found in onion in southern, central, and north-eastern regions and CaCV in tomato and chili peppers in northern and southern regions, respectively. Phylogenetic analysis of the nucleocapsid gene revealed segregation of field isolates of PBNV and WBNV into two distinct subclades, whereas isolates of CaCV and IYSV each clustered into a single clade. A proposal for establishing WBNV as a distinct tospovirus species is made based on the molecular characterization of small- (S) and medium- (M) RNA segments.