Most plant viruses rely on vector organisms for their plant-to-plant spread. Although there are many different natural vectors, few plant virus-vector systems have been well studied. This review ...describes our current understanding of virus transmission by aphids, thrips, whiteflies, leafhoppers, planthoppers, treehoppers, mites, nematodes, and zoosporic endoparasites. Strategies for control of vectors by host resistance, chemicals, and integrated pest management are reviewed. Many gaps in the knowledge of the transmission mechanisms and a lack of available host resistance to vectors are evident. Advances in genome sequencing and molecular technologies will help to address these problems and will allow innovative control methods through interference with vector transmission. Improved knowledge of factors affecting pest and disease spread in different ecosystems for predictive modeling is also needed. Innovative control measures are urgently required because of the increased risks from vector-borne infections that arise from environmental change.
Grapevine leafroll disease is caused by grapevine leafroll-associated viruses (GLRaVs). These viruses are common in vineyards worldwide and often associated with vitiviruses that are involved in the ...rugose wood complex of grapevine. Ten mealybug species are known as vectors of one or several of these grapevine viruses, including the apple mealybug Phenacoccus aceris which is widespread in Holarctic regions and able to transmit Grapevine leafroll-associated virus-1 and -3 (GLRaV-1 and -3). Our aim was to characterize the transmission features of leafroll viruses by Phenacoccus aceris in order to better understand the contribution of this mealybug to leafroll epidemics. Results showed that Phenacoccus aceris is able to transmit GLRaV-1, -3, -4, -5, -6, and -9 to grapevine but not GLRaV-7. This is the first report of GLRaV-6 transmission by a mealybug. Also, for the first time it was shown that Phenacoccus aceris could vector vitiviruses Grapevine virus A (GVA) and Grapevine virus B (GVB). First instar nymphs were the most efficient stage in transmitting GLRaV-1, -3, and GVA. This research sheds light on the transmission biology of grapevine viruses by Phenacoccus aceris and represents a step forward to leafroll disease management.
Ti-6Al-4V and stainless steel 316L have been processed by selective laser melting under similar conditions, and their microstructures and mechanical behaviours have been compared in details. Under ...the investigated conditions, Ti-6Al-4V exhibits a more complex behaviour than stainless steel 316L with respect to the occurrence of microstructural and mechanical anisotropy. Moreover, Ti-6Al-4V appears more sensitive to the build-up of internal stresses when compared with stainless steel 316L, whereas stainless steel 316L appears more prone to the formation of 'lack of melting' defects. This correlates nicely with the difference in thermal conductivity between the two materials. Thermal conductivity was shown to increase strongly with increasing temperature and the thermophysical properties appeared to be influenced by variations in the initial metallurgical state.
Grapevine Pinot gris virus (GPGV), belonging to the genus Trichovirus of the family Betaflexiviridae, was first identified by siRNA sequencing in northern Italy in 2012, in the grapevine varieties ...Pinot gris, Traminer, and Pinot Noir, which exhibited mottling and leaf deformation (1), and in asymptomatic vines, with a lower frequency. Since 2012, this virus has also been reported in South Korea, Slovenia, Greece (3), Czech Republic (2), Slovakia (2), and southern Italy (4). In 2014, GPGV was identified by Illumina sequencing of total RNAs extracted from leaves of the Merlot variety (Vitis vinifera) grafted onto Gravesac rootstock originated from a vineyard in the Bordeaux region of France. This Merlot plant exhibited fanleaf-like degeneration symptoms associated with Tomato black ring virus (TBRV) infection. Cuttings were collected in 2010 and maintained thereafter in a greenhouse. The full-length genome was assembled either de novo or by mapping of the Illumina reads on a reference GPGV genome (GenBank FR877530) using the CLC Genomics workbench software (CLC Bio, Qiagen, USA). The French GPGV isolate "Mer" (7,223 nucleotides, GenBank KM491305) is closely related to other European GPGV sequences; it exhibits 95.4% nucleotide identity with the reference Italian isolate (NC_015782) and 98 to 98.3% identity with Slovak isolates (KF134123 to KF134125). The higher divergence between French and Italian GPGV isolates was mainly due to differences in the 5' extremity of the genome, as already shown with the Slovak GPGV isolates. RNA extracted from phloem scrapings of 19 cv. Merlot vines from the same plot collected in 2014 were analyzed by RT-PCR using the specific primer pair Pg-Mer-F1 (5'-GGAGTTGCCTTCGTTTACGA-3') and Pg-Mer-R1 (5'-GTACTTGATTCGCCTC GCTCA-3'), designed on the basis of alignments of all available GPGV sequences from GenBank. The resulting amplicon of 770 bp corresponded to a fragment of the putative movement protein (MP) gene. Seven (35%) of the tested plants gave a strong positive amplification. Three RT-PCR products were directly sequenced and showed 99.3 to 99.5% identity within the MP gene of the GPGV-Mer isolate. Given the mixed viral infection status of the vines found infected by GPGV, it was not possible to associate a specific symptomatology with the presence of GPGV. Furthermore, similar RT-PCR tests were also performed on RNA extracts prepared from two plants of cv. Carignan that originated from a French grapevine collection, exhibiting fanleaf-like symptoms without any nepovirus detection. These samples similarly gave a strong positive amplification. The sequences obtained from the two Carignan vines showed 98.4 and 97.8% identity with the GPGV-Mer isolate. To our knowledge, this is the first report of GPGV in France. GPGV has been discovered in white and red berry cultivars, suggesting that its prevalence could be important in European vineyards (2). Further large-scale studies will be essential to determine the world prevalence of GPGV and to evaluate its potential effects on yield and on wine quality, as well as to shed light on GPGV epidemiology. Of particular concern is whether, like the other grapevine-infecting Trichovirus, Grapevine berry inner necrosis virus (GPGV) can be transmitted by the eryophid mite Colomerus vitis. References: (1) A. Giampetruzzi et al. Virus Res. 163: 262, 2012. (2) M. Glasa et al. Arch. Virol. 159: 2103, 2014. (3) G. P. Martelli, J. Plant Pathol. 96: S105, 2014. (4) M. Morelli et al. J. Plant Pathol. 96:431, 2014.
Data mining and metagenomic analysis of 277 open reading frame sequences of bipartite RNA viruses of the genus
Nepovirus
, family
Secoviridae
, were performed, documenting how challenging it can be ...to unequivocally assign a virus to a particular species, especially those in subgroups A and C, based on some of the currently adopted taxonomic demarcation criteria. This work suggests a possible need for their amendment to accommodate pangenome information. In addition, we revealed a host-dependent structure of arabis mosaic virus (ArMV) populations at a cladistic level and confirmed a phylogeographic structure of grapevine fanleaf virus (GFLV) populations. We also identified new putative recombination events in members of subgroups A, B and C. The evolutionary specificity of some capsid regions of ArMV and GFLV that were described previously and biologically validated as determinants of nematode transmission was circumscribed
in silico
. Furthermore, a C-terminal segment of the RNA-dependent RNA polymerase of members of subgroup A was predicted to be a putative host range determinant based on statistically supported higher π (substitutions per site) values for GFLV and ArMV isolates infecting
Vitis
spp. compared with non-
Vitis
-infecting ArMV isolates. This study illustrates how sequence information obtained via high-throughput sequencing can increase our understanding of mechanisms that modulate virus diversity and evolution and create new opportunities for advancing studies on the biology of economically important plant viruses.
Post-transcriptional gene silencing (PTGS), or RNA silencing, is one of the key mechanisms of antiviral defence used by plants. To counter this defence response, viruses produce suppressor proteins ...that are able to inhibit the PTGS pathway or to interfere with some of its function. The aim of this study was to evaluate the RNA silencing suppressor (RSS) activity of P0 proteins from selected European isolates of the beet-infecting poleroviruses beet chlorosis virus (BChV) and beet mild yellowing virus (BMYV) using two different experimental systems: (i) agro-infiltration of Nicotiana benthamiana green fluorescent protein-positive plants and (ii) mechanical inoculation of Chenopodium quinoa using a beet necrotic yellow vein virus (BNYVV, genus Benyvirus) RNA3-based replicon. The results demonstrated that P0 of most BMYV isolates exhibited RSS activity, although at various efficiencies among isolates. Conversely, P0 of BChV isolates displayed no RSS activity in either of the two systems under the experimental conditions used. These results are the first reported evidence that P0 proteins of two closely related beet poleroviruses show strain-specific differences in their effects on RNA silencing.
The isometric virus Grapevine redglobe virus (GRGV), was first described on grapevine cv. Red Globe in southern Italy in 2000 (3) and later in Greece and California. GRGV belongs to the genus ...Maculavirus in the family Tymoviridae. These viruses are thought to be disseminated through propagation and grafting, as no vectors or seed transmission are known to date. A partial sequence (2,006 nucleotides nt) encompassing the 3' end of the replicase, the coat protein, and P17 genes, was obtained in 2003 (1). GRGV infections are apparently symptomless (2). In 2014, GRGV was identified by Illumina sequencing of total RNAs extracted from a Vitis vinifera cv. Cabernet franc (CF) vine grafted onto Gravesac in a vineyard of the Bordeaux region in France. This Cabernet franc plant displayed fanleaf-like degeneration symptoms associated with Tomato black ring virus (TBRV) infection. It had been collected in 2010 and maintained since in a greenhouse. The partial contigs assembled from the Illumina reads (552 and 430 nt, both in the putative replicase gene, KM491303 and KM491304) showed 85.9 and 86.3% nt identity with the partial sequence of a GRGV Italian isolate (AF521577), respectively. Total RNA extracts from leaves of 18 plants of cv. Cabernet franc from the same plot, collected in 2014, were analyzed by RT-PCR using specific primers RG-CF-F1 (5'-GAATTCGCTGTCGGCCACTC-3') and RG-CF-R1 (5'-AGTGAGAGGAGAGATTCCATC-3') designed on the basis of the alignment of the partial sequences of GRGV-CF and the Italian isolate (AF521577). Fifteen (83%) of the plants gave strong positive amplification for GRGV. Given the mixed viral infection status of these vines, it was not possible to associate a specific symptomatology with the presence of GRGV. Two RT-PCR amplicons were directly sequenced and showed 91.5 and 91.7% identities, respectively, with the reference GRGV-CF sequence. To our knowledge, this is the first report of GRGV in France. Further studies will be necessary to determine the prevalence of GRGV in the French vineyards and varieties, including rootstocks, and its possible threat to the grapevine industry. Studies are also needed to assess the pathogenicity of GRGV. Similarly to its close relative, Grapevine fleck virus, does it induce latent or semi-latent infections in Vitis vinifera and rootstock hybrids, influencing vigor, rooting ability, and graft compatibility? References: (1) N. Abou Ghanem-Sabanadzovic et al. Virus Genes 27:11, 2003. (2) G. P. Martelli et al. Arch. Virol. 147:1847, 2002. (3) S. Sabanadzovic et al. Arch. Virol. 145:553, 2000.
In order to determine the etiology of Syrah decline, virus detection was performed on 22 Syrah clones, chosen for their various levels of sensitivity to Syrah decline. All clones, including the ...sensitive ones, were free of 20 main grapevine viruses. In contrast,
Grapevine Syrah virus
-1 and
Grapevine Rupestris stem pitting-associated virus
(GRSPaV), were detected in 56 % and 100 % of the analysed Syrah clones respectively. This is the first report of GSyV-1 in a French vineyard. The genetic diversity of a 380 nt region within the GRSPaV coat protein gene was studied extensively in vines differing in their sensitivity to Syrah decline. Most GRSPaV variants were scattered between the four phylogenetic groups previously identified; 65 % of the sequences analysed were found to belong to the GRSPaV—group 1, 22 % to—group 2b, 10 % to—group 2a and 2 % to—group 3. Seventy percent of the 31 plants analysed harboured mixtures of genomic variants. Statistical analyses revealed no significant correlation between sensitivity and GRSPaV sequence variation. This suggests that GRSPaV is not the direct etiological agent of the Syrah decline.
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