Prevalence and genetic diversity of viruses associated with rugose wood complex in Greek vineyards

Rugose wood is one of the most important disease syndromes of grapevine and it has been associated with at least three viruses: grapevine rupestris stem pitting associated virus (GRSPaV), grapevine virus A (GVA) and grapevine virus B (GVB). All three viruses show a worldwide distribution pattern, and their genetic composition has been the focus of extensive research over the past years. Despite their first record in Greece almost 20 years ago, there is a lack of knowledge on the distribution and genetic variability of their populations in Greek vineyards. In this context, we investigated the distribution of GRSPaV, GVA and GVB in rootstocks, self-rooted and grafted grapevine cultivars, originating from different geographic regions that are representing important viticultural areas of Greece. Three new RT-PCR assays were developed for the reliable detection of GRSPaV, GVA and GVB. Our results indicated that GVA is the most prevalent in Greek vineyards, followed by GRSPaV and GVB. However, virus incidence differed among self-rooted and grafted grapevine cultivars or rootstocks tested. Selected isolates from each virus were further molecularly characterized to determine their phylogenetic relationships. All three viruses exhibited high nucleotide diversity, which was depicted in the constructed phylogenetic trees. Isolates from Greece were placed in various phylogroups, reinforcing the scenario of multiple introductions of GVA, GVB and GRSPaV in Greece and highlighting the effect of different transmission modes in the evolutionary course of the three viruses.

Cultivated and wild grapevines in Tennessee possess overlapping but distinct virus populations

Viruses and viroids prevalent in a population of 42 wild grapevines (i.e., free-living, uncultivated grapevines; Vitis spp.) were compared to those in a population of 85 cultivated grapevines collected in Tennessee, USA by RNA-seq analysis of pools of ribosomal RNA-depleted total RNA. The sequences of 10 viruses (grapevine fleck virus, grapevine leafroll-associated virus 2, grapevine rupestris stem pitting-associated virus, grapevine Syrah virus 1, grapevine vein-clearing virus, grapevine virus B, grapevine virus E, tobacco ringspot virus, tomato ringspot virus and a novel nano-like virus) and two viroids (hop stunt viroid and grapevine yellow speckle viroid 1) were detected in both grapevine populations. Sequences of four viruses (grapevine associated tymo-like virus, grapevine leafroll-associated virus 3, grapevine red blotch virus and grapevine virus H) were identified only from cultivated grapevines. High, moderate and low numbers of sequence reads were identified only from wild grapevines for a novel caulimovirus, an enamovirus, and alfalfa mosaic virus, respectively. The presence of most virus sequences and both viroids was verified independently in the original samples by reverse transcription-polymerase chain reaction followed by Sanger sequencing. Comparison of viral sequences shared by both populations showed that cultivated and wild grapevines harbored distinct sequence variants, which suggests that there was limited virus movement between the two populations. Collectively, this study represents the first unbiased survey of viruses and viroids in both cultivated and wild grapevines within a defined geographic region.

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.

A Survey of Virginia Vineyards Revealed High Incidences of Grapevine Rupestris Stem Pitting-Associated Virus, Grapevine Red Blotch Virus, and Two Mealybug Species

We investigated the prevalence of viruses infecting grapevines in Virginia, identity of disease vectors, and potential factors affecting virus incidence. Tested viruses were grapevine leafroll-associated virus (GLRaV-1 and -4), grapevine fleck virus (GFkV), grapevine virus A (GVA), grapevine virus B (GVB), grapevine rupestris stem pitting-associated virus (GRSPaV), tomato ringspot virus (ToRSV), grapevine vein clearing virus (GVCV), grapevine red blotch virus (GRBV), and grapevine Pinot gris virus (GPGV). We documented wide distributions of GRSPaV (54%) and GRBV (24%) and common occurrences of grape (Pseudococcus maritimus) and Gill’s (Ferrisia gilli) mealybugs among vineyards. This is the first report of GLRaV-1, GLRaV-4, GVA, GVB, GRSPaV, and obscure mealybug (Pseudococcus viburni) in Virginia. We also documented significant association (P ≤ 0.05) of the presence of mealybugs and GVA and GVB. With younger vines, significantly lower incidences were found for viruses that were listed (i.e., tested for a certification) by the Foundation Planting Service’s and the National Clean Plant Network’s grape programs. On the other hand, there was a lack of the age effect on incidence of GRSPaV and GRBV, which were not listed until recently. These results suggest the importance of clean plant material and vector management for grapevine virus disease management in Virginia.

Prevalence of Viruses in Commercial Wine Grape Vineyards in Georgia

Virus diseases are major constraints to Vitis vinifera wine grape production worldwide. Grapevine leafroll-associated virus 3 (GLRaV-3) was first confirmed in Georgia in 2008. The negative impacts of GLRaV-3, such as decreased fruit yield and quality, were confirmed from samples taken in 2009 and 2010. In light of these findings, studies were initiated to determine the prevalence and types of grapevine viruses present in vineyards in Georgia. Five vineyard blocks were visited during August and September of 2011 and 2012. Leaf samples were collected from a total of 50 grapevines showing symptoms of and suspected as being infected by grapevine leafroll disease (GLD). Samples from individual grapevines were extracted and tested separately for 20 grapevine viruses listed in standard virus indexing programs. Reverse transcription polymerase chain reaction (RT-PCR) or PCR, depending on the nature of the virus genome, was used to detect these viruses with species-specific primers. The results showed the presence of GLRaV-1, -2, -3, and -4 (strains 4, 5, and 6), grapevine virus B, grapevine rupestris stem pitting-associated virus, and grapevine red blotch virus. Many vineyards had multiple viruses detected from individual grapevines showing typical GLD or GLD-like symptoms.