Grapevine Pinot Gris Virus Is Present in Different Non-Vitis Hosts

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.

New Host Plant Species of Grapevine Virus A Identified with Vector-Mediated Infections

Grapevine virus A (GVA) is an economically important virus and a member of the genus Vitivirus (family Betaflexiviridae) that causes a range of symptoms with qualitative and quantitative effects on grape production. Wild and domesticated species of Vitis, including hybrids used as rootstocks, are considered important natural hosts of GVA. Mechanical transmission to some herbaceous plant species, graft transmission, and vector transmission from grape to grape by various mealybugs and soft scale insects have been reported. Under laboratory and greenhouse conditions, this study demonstrates the transmission of GVA from grapes to alternative hosts by the vine mealybug (Planococcus ficus). Results of ELISA, end-point one-step RT-PCR, and real-time RT-PCR, and in some cases electron microscopy and genome sequencing, confirmed successful transmission to three new plant species commonly found in Croatian vineyards: velvetleaf (Abutilon theophrasti), redroot pigweed (Amaranthus retroflexus), and field poppy (Papaver rhoeas), along with Chenopodium murale and the previously known host Nicotiana benthamiana, with variable infection rates. Depending on the host species, symptoms in the form of leaf reddening, yellow spots, reduced growth of lateral shoots, systemic vein clearing, foliar deformation and rugosity, and dwarfism were observed in GVA-infected plants, whereas no symptoms were observed in infected plants of A. theophrasti. Reverse transmission from these new hosts to grapevines by Pl. ficus was not successful. These results confirm four new GVA host species and open new research venues.

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.

Potential Implications and Management of Grapevine Viruses in Mexico: A Review

Worldwide, virus infections in grapevines are of concern due to the potential for economic loss. Although the grape industry in Mexico is relatively small and focused mainly on the local market, production dates back to the time of the Spanish colonization. This manuscript discusses the findings on grapevine viruses in Mexico. Nine viruses have been identified in the last fifty years, including grapevine red blotch virus (GRBV), grapevine leafroll-associated virus 3 (GLRaV-3), grapevine fanleaf virus (GFLV), and grapevine virus A (GVA). Important information is provided about these viruses and viral pathogens that have not yet been reported in Mexico, but represent an ongoing threat to plant health and grapevine production in other viticultural regions of the world. Strategies for virus control in vineyards are described. The information discussed here should be shared with growers and stakeholders to prevent future negative impacts on the Mexican grapevine industry and to save ancient grapevine accessions.

Biology and Ultrastructural Characterization of Grapevine Badnavirus 1 and Grapevine Virus G

The biological characteristics of grapevine viruses, such as their transmission and host range, are important for the adoption of successful prophylaxis strategies. The aim of this study was to investigate the traits of two newly described grapevine viruses widely distributed in Croatia, grapevine badnavirus 1 (GBV-1) and grapevine virus G (GVG). The vine mealybug (Planoccocus ficus) proved to be a vector of GBV-1 and GVG capable of vine-to-vine transmission with overall experimental transmission rates of 61% and 14.6%, respectively. Transmission was also demonstrated by grafting, with an overall transmission rate of 53.8% for GBV-1 and 100% for GVG, as well as by green grafting using the T-budding technique. Symptoms of GBV-1 and GVG were not observed on the woody cylinders of the indicators LN 33, Kober 5BB, 110 Richter and cvs. Chardonnay and Cabernet Sauvignon. Seed transmission and mechanical transmission were not confirmed. Electron microscopy revealed accumulation of GBV-1 particles and viroplasms in the cytoplasm, but no alternations of the cell structure. Infection with GVG revealed the proliferation of tonoplast-associated vesicles inside phloem cells and cell wall thickening.