Grapevine Pinot gris virus spreads in infected vineyards: latent infections have no direct impact on grape production.

BACKGROUND: Grapevine Pinot gris virus (GPGV) infects grapevines worldwide and causes symptoms such as chlorotic mottling and deformations on leaves, stunted shoots and short panicles, or none of these symptoms if it appears as latent infection. So far, the consequences of GPGV infections for winegrowers are difficult to assess since important information such as plant performance at different GPGV infection levels and symptom expression are not fully clarified. METHODS: In order to investigate the course of GPGV spread, annual visual evaluations and ELISA tests were conducted over 3-4 consecutive years in four GPGV-infected vineyards in southern Germany: GEM, HEC, NIM, and REI. The program PATCHY was used to analyze spatial disease patterns. Sanger sequencing was used to determine virus isolates in vines at different GPGV infection levels, to test their respective influence on symptom expression. Yield and GrapeScan (FTIR) analyses were conducted to test the impact of different GPGV infection levels and isolates on fruit quantity and quality. RESULTS: GPGV infections significantly increased in all four vineyards (GEM 22-32%, HEC 50-99%, NIM 83-90%, REI 56-76%) with significant spreading patterns across and along rows. Specific symptom progression patterns were not observed. According to our results, the virus isolate has an influence on whether symptoms develop during a GPGV infection. While yield analyses revealed that yield losses only occur in symptomatic vines and range from 13 to 96% depending on the severity of symptoms, latent infections have no impact on grape production. No relevant effects of GPGV infections on must quality were observed. CONCLUSIONS: Secondary spread of GPGV was observed in all vineyards monitored, indicating vector-borne transmission that is likely to be accelerated by human viticultural management. GPGV should be further monitored to prevent the accumulation of detrimental symptomatic isolates. The results of this study can be used to assess the risk of GPGV to viticulture and should be considered when developing management strategies against the virus.

The recent importation of Grapevine Pinot gris virus into Australia.

A total of 575 commercial grapevine (Vitis vinifera) samples from Australia have been tested for a newly emerging virus, Grapevine Pinot gris virus (Trichovirus, Betaflexiviridae) during 2015-2017. Nine samples from two states tested positive. Six of these were from New South Wales and 3 from South Australia in a total of eight varieties. All these varieties were imported from Europe within the last 4-19 years. A fragment of 431 nucleotides on the coat protein gene of Grapevine Pinot gris virus was targeted for virus identification by RT-PCR. The virus specificity of each positive sample was confirmed by sequencing followed by the BLASTn analysis which showed an identity of up to 99.3% to the virus sequences in the NCBI database. The phylogenetic tree as well as pairwise sequence identity showed that, although the virus sequence in each variety was unique, they all grouped with the isolates from Europe and well away from the South Korean and several Chinese isolates. This is the first report of the occurrence of Grapevine Pinot gris virus in Australia.

Effect of repeated Ribavirin treatment on grapevine viruses.

The effect of Ribavirin treatment for the chemotherapy of several grapevine viruses was evaluated. Four grapevine cultivars were repeatedly treated with Ribavirin in two different concentrations and with three different lengths of treatment. Repeating the Ribavirin treatment always had a significant effect on the number of healthy grapevine plants obtained. Ribavirin concentration and length of exposure showed a significant difference in sanitation of the Grapevine rupestris stem pitting-associated virus. During sanitation of the Grapevine Pinot gris virus and Grapevine fleck virus, those two factors did not show significant differences in the elimination of grapevine viruses.

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.

Occurrence and Genetic Characterization of Grapevine Pinot Gris Virus in Russia.

Grapevine Pinot gris virus (GPGV) is a widespread grapevine pathogen associated with symptoms of leaf mottling and deformation. In order to study the distribution and genetic diversity of GPGV in Russia, we tested 1347 grapevine samples from 3 regions of Russia-the Krasnodar Krai, Stavropol Krai, and Republic of Crimea-using duplex real-time RT-PCR. GPGV was detected in 993 grapevines, both symptomatic and asymptomatic. In 119 isolates, we sequenced complete movement protein (MP) and coat protein (CP) genes of the GPGV genome. The percentage of identity of the obtained nucleotide MP/CP sequences with the closest isolates from the GenBank was 97.75-99.56%. A phylogenetic analysis showed that these Russian GPGV isolates are mainly grouped with previously described representative asymptomatic isolates. New post-translational modifications of the MP and CP at the positions of polymorphisms in the genomes of Russian isolates were predicted. The present work is the first study on the distribution and genetic diversity of GPGV in Russia.

Polymorphisms at the 3'end of the movement protein (MP) gene of grapevine Pinot gris virus (GPGV) affect virus titre and small interfering RNA accumulation in GLMD disease.

Grapevine Leaf Mottling and Deformation (GLMD) is a grapevine disease that has been associated with a trichovirus, the grapevine Pinot gris virus (GPGV). A wide diversity in the severity of GLMD disease symptoms has been recorded worldwide, but the relationship of this diversity to the sequence variation in the GPGV genome is still a matter of debate. Results from comparative analysis of GPGV genomic sequences have suggested an association of polymorphisms at the 3'-end of the movement protein (MP) with GLMD severity. Here, the 3'-terminus of the MP gene of a GPGV infectious clone derived from an isolate from grapevine showing severe symptoms (fvg-12), was substituted with a 356 bp synthetic DNA fragment having a sequence resembling that of another GPGV isolate (fvg-15), recovered from an asymptomatic grapevine. The clone containing this chimeric construct was root-inoculated in virus-free Kober rootstocks along with the clones containing the fvg-12 and fvg-15 full length sequence. Remarkable differences in virus titre, accumulation of GPGV-derived small interfering RNAs (siRNAs), alterations in the gene expression of boron transporters and, to a lesser extent, in symptom expression were recorded among plants infected with either one of the three GPGV derived clones. In particular, the chimeric clone behaviour was indistinguishable from that of the donor of the small 356 bp fragment and significantly different from the other. Thus, this work experimentally confirmed the critical role of the GPGV-MP C-terminus in determining the fate of the infection, as it had been previously hypothesized on the basis of comparative sequence analysis.

Studies on the Occurrence of Viruses in Planting Material of Grapevines in Southwestern Germany.

Viral diseases in viticulture lead to annual losses in the quantity and quality of grape production. Since no direct control measures are available in practice, preventive measures are taken to keep the vines healthy. These include, for example, the testing of propagation material for viruses such as Arabis mosaic virus (ArMV), Grapevine fanleaf virus (GFLV) or Grapevine leafroll-associated virus 1 (GLRaV-1) and 3 (GLRaV-3). As long-term investigations have shown, GLRaV-1 (2.1%) occurs most frequently in southwestern German wine-growing regions, whereas GLRaV-3 (<0.1%) is almost never found. However, tests conducted over 12 years indicate that there is no general decline in virus-infected planting material. Thus, it can be assumed that a spread of the viruses via corresponding vectors still takes place unhindered. Beyond the examinations regulated within the German Wine Growing Ordinance, one-time tests were carried out on Grapevine Pinot gris virus (GPGV). This analysis showed that GPGV was found in 17.2% of the samples.

Survey and Diversity of Grapevine Pinot gris virus in Algeria and Comprehensive High-Throughput Small RNA Sequencing Analysis of Two Isolates from Vitis vinifera cv. Sabel Revealing High Viral Diversity.

Grapevine Pinot gris virus (GPGV) is a putative causal agent of grapevine leaf mottling and deformation disease that has been reported worldwide throughout the grapevine-growing regions. Fifty-four grapevines collected from five Algerian grapevine-growing regions were tested for the presence of GPGV in phloem tissues. Eight of the tested grapevines were infected by GPGV. Viromes of two selected Vitis vinifera cv. Sabel grapevines infected by GPGV and showing virus-like symptoms were analyzed by small RNA sequencing. Phylogenetic analyses of the partial coding sequence (cds) of the RNA-dependent RNA polymerase (RdRp) domain showed that all Algerian GPGV isolates were grouped with some already-described asymptomatic isolates. This study provides the first survey of the occurrence of GPGV in Algeria. Moreover, Grapevine fleck virus, Grapevine rupestris stem pitting-associated virus, Grapevine virus B, Grapevine rupestris vein feathering virus, Hop stunt viroid and Grapevine yellow speckle viroid 1 were detected in Algeria for the first time.

With or Without You: Altered Plant Response to Boron-Deficiency in Hydroponically Grown Grapevines Infected by Grapevine Pinot Gris Virus Suggests a Relation Between Grapevine Leaf Mottling and Deformation Symptom Occurrence and Boron Plant Availability.

Despite the increasing spread of Grapevine Leaf Mottling and Deformation (GLMD) worldwide, little is known about its etiology. After identification of grapevine Pinot gris virus (GPGV) as the presumptive causal agent of the disease in 2015, various publications have evaluated GPGV involvement in GLMD. Nevertheless, there are only partial clues to explain the presence of GPGV in both symptomatic and asymptomatic grapevines and the mechanisms that trigger symptom development, and so a consideration of new factors is required. Given the similarities between GLMD and boron (B)-deficiency symptoms in grapevine plants, we posited that GPGV interferes in B homeostasis. By using a hydroponic system to control B availability, we investigated the effects of different B supplies on grapevine phenotype and those of GPGV infection on B acquisition and translocation machinery, by means of microscopy, ionomic and gene expression analyses in both roots and leaves. The transcription of the genes regulating B homeostasis was unaffected by the presence of GPGV alone, but was severely altered in plants exposed to both GPGV infection and B-deficiency, allowing us to speculate that the capricious and patchy occurrence of GLMD symptoms in the field may not be related solely to GPGV, but to GPGV interference in plant responses to different B availabilities. This hypothesis found preliminary positive confirmations in analyses on field-grown plants.