Characterization of a New, Country Bean (Lablab purpureus) Lineage of Bean Common Mosaic Necrosis Virus.

Country bean (Lablab purpureus, family Fabaceae) is grown in subsistence agriculture in Bangladesh as a multipurpose crop for food, animal feed, and green manure. This study was undertaken to investigate the genetic diversity of bean common mosaic necrosis virus (BCMNV, genus Potyvirus, family Potyviridae) in country beans. Leaf samples from country beans showing yellowing, vein banding, and mosaic symptoms were collected during field surveys between 2015 and 2019 cropping seasons from farmers' fields in different geographic regions. These samples were tested by serological and molecular diagnostic assays for the presence of BCMNV. Virus-positive samples were subjected to high-throughput Illumina sequencing to generate near-complete genomes of BCMNV isolates. In pairwise comparisons, the polyprotein sequences of BCMNV isolates from Bangladesh showed greater than 98% identities among themselves and shared less than 84% sequence identity at the nucleotide level with virus isolates reported from other countries. In the phylogenetic analysis, BCMNV isolates from Bangladeshi country beans formed a separate clade from virus isolates reported from common beans in other countries in the Americas, Africa, Europe, and from East Timor. Grow-out studies showed seed-to-seedling transmission of BCMNV, implying a possible seedborne nature of the virus in country beans.

Molecular characterization of a novel gammacarmovirus infecting cucurbits in India.

In this study, we describe the identification of a new gammacarmovirus infecting Cucurbita pepo plants showing a range of mosaic, stunting, yellowing, and wilting symptoms. The virus had a narrow host range and mostly produced chlorotic and necrotic local lesions in the majority of the tested plants. However, Nicotiana benthamiana showed systemic symptoms under laboratory conditions. Using a combination of Sanger sequencing and rapid amplification of cDNA ends (RACE), the complete genome sequence of the virus was determined to be 4274 nucleotides (nt) in length. Its genome organization is similar to that of members of the genus Gammacarmovirus in the family Tombusviridae, consisting of five overlapping open reading frames (ORFs) encoding p28, replicase, p7A, p7B, and coat protein (CP), respectively. The genome is flanked by short 5' and 3' non-coding regions (NCR) at either end. In pairwise comparisons of replicase and CP sequences, the virus showed the highest amino acid sequence identity of 71.55% and 54.86%, respectively, to melon necrotic spot virus (MNSV), the type member of the genus Gammacarmovirus. Since the sequence identity values are below the species demarcation threshold suggested by the International Committee on Taxonomy of Viruses (ICTV), the virus from Cucurbita pepo plants, for which the name "cucurbit carmovirus" (CuCV) is proposed, represents a new species. In phylogenetic analysis based on the replicase and CP amino acid sequences, CuCV clustered with MNSV but formed a distinct branch, further confirming that the virus is a distinct member of the genus Gammacarmovirus.

Spatio-Temporal Spread of Grapevine Leafroll Disease in Washington State Vineyards.

The spread of grapevine leafroll disease (GLD) to vineyards planted with certified planting stock is of significant concern to grape growers. In this study, the spatial and temporal spread of GLD was examined in three vineyard blocks planted with virus-tested wine grape (Vitis vinifera) cultivars adjacent to vineyard blocks heavily infected with GLD in two geographic locations in eastern Washington State. During each season, the position of vines showing GLD symptoms was recorded in a matrix representing the planting lattice. Symptomatic vines were positive only for Grapevine leafroll-associated virus 3 (GLRaV-3), the most common virus species consistently associated with GLD in Washington vineyards. The results from multiple seasons showed a gradual increase in disease incidence over time in all three blocks. Spatial and temporal mapping of GLD indicated a disease gradient in which the highest percentage of symptomatic vines was in rows proximal to infected old blocks. Spatial autocorrelation analysis using Moran's I values suggested random patterns of symptomatic vines in the three blocks during initial years, indicating primary spread of the virus not related to infected vines within the block. Clustering at the scale of neighboring vines during subsequent years suggested secondary spread within the block. Results of quadrat-based spatial analyses of GLD incidence were compared with previously reported data obtained from California and elsewhere for an improved understanding of the dynamics of GLD spread to facilitate area-wide disease management strategies.

Intra-species recombination among strains of the ampelovirus Grapevine leafroll-associated virus 4.

BACKGROUND: Grapevine leafroll disease is one of the most economically important viral diseases affecting grape production worldwide. Grapevine leafroll-associated virus 4 (GLRaV-4, genus Ampelovirus, family Closteroviridae) is one of the six GLRaV species documented in grapevines (Vitis spp.). GLRaV-4 is made up of several distinct strains that were previously considered as putative species. Currently known strains of GLRaV-4 stand apart from other GLRaV species in lacking the minor coat protein. METHODS: In this study, the complete genome sequence of three strains of GLRaV-4 from Washington State vineyards was determined using a combination of high-throughput sequencing, Sanger sequencing and RACE. The genome sequence of these three strains was compared with corresponding sequences of GLRaV-4 strains reported from other grapevine-growing regions. Phylogenetic analysis and SimPlot and Recombination Detection Program (RDP) were used to identify putative recombination events among GLRaV-4 strains. RESULTS: The genome size of GLRaV-4 strain 4 (isolate WAMR-4), strain 5 (isolate WASB-5) and strain 9 (isolate WALA-9) from Washington State vineyards was determined to be 13,824 nucleotides (nt), 13,820 nt, and 13,850 nt, respectively. Multiple sequence alignments showed that a 11-nt sequence (5'-GTAATCTTTTG-3') towards 5' terminus of the 5' non-translated region (NTR) and a 10-nt sequence (5'-ATCCAGGACC-3') towards 3' end of the 3' NTR are conserved among the currently known GLRaV-4 strains. LR-106 isolate of strain 4 and Estellat isolate of strain 6 were identified as recombinants due to putative recombination events involving divergent sequences in the ORF1a from strain 5 and strain Pr. CONCLUSION: Genome-wide analyses showed for the first time that recombinantion can occur between distinct strains of GLRaV-4 resulting in the emergence of genetically stable and biologically successful chimeric viruses. Although the origin of recombinant strains of GLRaV-4 remains elusive, intra-species recombination could be playing an important role in shaping genetic diversity and evolution of the virus and modulating the biology and epidemiology of GLRaV-4 strains.

Sequence analysis of the medium and small RNAs of impatiens necrotic spot virus reveals segment reassortment but not recombination.

The complete sequence of the medium (M) and small (S) RNA genome segments were determined for twelve isolates of impatiens necrotic spot virus from eight plant species. The M- and S-RNAs of these isolates shared 97-99% and 93-98% nucleotide sequence identity, respectively, with the corresponding full-length sequences available in public databases. Phylogenetic analysis based on the M- or S-RNA sequences showed incongruence in the phylogenetic position of some isolates, suggesting intraspecies segment reassortment. The lack of phylogenetic discordance in individual and concatenated sequences of individual genes encoded by M- or S-RNAs suggests that segment reassortment rather than recombination is driving evolution of these INSV isolates.

Global Dimensions of Plant Virus Diseases: Current Status and Future Perspectives.

Viral diseases provide a major challenge to twenty-first century agriculture worldwide. Climate change and human population pressures are driving rapid alterations in agricultural practices and cropping systems that favor destructive viral disease outbreaks. Such outbreaks are strikingly apparent in subsistence agriculture in food-insecure regions. Agricultural globalization and international trade are spreading viruses and their vectors to new geographical regions with unexpected consequences for food production and natural ecosystems. Due to the varying epidemiological characteristics of diverent viral pathosystems, there is no one-size-fits-all approach toward mitigating negative viral disease impacts on diverse agroecological production systems. Advances in scientific understanding of virus pathosystems, rapid technological innovation, innovative communication strategies, and global scientific networks provide opportunities to build epidemiologic intelligence of virus threats to crop production and global food security. A paradigm shift toward deploying integrated, smart, and eco-friendly strategies is required to advance virus disease management in diverse agricultural cropping systems.

Complete Genome Segment Sequences of Tomato Chlorotic Spot Virus from Peanut in Haiti.

Tomato chlorotic spot virus (TCSV) is emerging as a significant constraint to vegetable and legume crops in the Americas. The complete genome sequence of a TCSV isolate naturally infecting peanut (Arachis hypogea) in Haiti was determined in the effort to build epidemiological knowledge of the virus.

Taxonomy of the order Bunyavirales: second update 2018.

In October 2018, the order Bunyavirales was amended by inclusion of the family Arenaviridae, abolishment of three families, creation of three new families, 19 new genera, and 14 new species, and renaming of three genera and 22 species. This article presents the updated taxonomy of the order Bunyavirales as now accepted by the International Committee on Taxonomy of Viruses (ICTV).

The Relative Occurrence of Grapevine leafroll-associated virus 3 and Grapevine red blotch virus in Washington State Vineyards.

Vineyard surveys were conducted for three consecutive seasons in eastern Washington State, the major grapevine-growing region in the state, to document the occurrence of Grapevine leafroll-associated virus 3 (GLRaV-3) and Grapevine red blotch virus (GRBV). The majority of samples were collected from red-berried wine grape (Vitis vinifera) cultivars exhibiting symptoms of or suspected for grapevine leafroll (GLD) and red blotch (GRBD) diseases. A limited number of samples from white-berried cultivars were collected randomly due to the lack of visual symptoms. Samples were collected from a total of 2,063 grapevines from 18 red-berried cultivars and seven white-berried cultivars planted in eight American Viticultural Areas and tested for GLRaV-3 and GRBV using RT-PCR and PCR, respectively. The results showed 67.77% and 6.01% of total samples positive for GLRaV-3 and GRBV, respectively, and 9.06% of samples positive for both viruses. About 17% of samples tested negative for the two viruses, but some of these samples were positive for GLRaV-2 and GLRaV-4. Overall results indicated that GLRaV-3 was more common than GRBV, independent of cultivars and the geographic origin of samples. Due to variability in symptoms in red-berried cultivars, virus-specific diagnostic assays were deemed necessary for reliable identification of GLRaV-3 and GRBV and to differentiate GLD and GRBD symptoms from those induced by biotic and abiotic stresses in vineyards. A multiplex PCR protocol was developed for simultaneous detection of GLRaV-3 and GRBV in grapevine samples. A global phylogenetic analysis of GRBV genome sequences revealed segregation of virus isolates from Washington State vineyards into two distinct clades, with the majority of isolates belonging to clade II.

Development of infectious cDNA clones of Grapevine leafroll-associated virus 3 and analyses of the 5' non-translated region for replication and virion formation.

Infectious cDNA clones were developed for Grapevine leafroll-associated virus 3 (GLRaV-3, genus Ampelovirus, family Closteroviridae). In vitro RNA transcripts generated from cDNA clones showed replication via the production of 3'-coterminal subgenomic (sg) mRNAs in Nicotiana benthamiana protoplasts. The detection of sgRNAs and the recovery of progeny recombinant virions from N. benthamiana leaves agroinfiltrated with full-length cDNA clones confirmed RNA replication and virion formation. The 5' non-translated region (5' NTR) of GLRaV-3 was exchangeable between genetic variants and complement the corresponding cognate RNA functions in trans. Mutational analysis of the 5' NTR in minireplicon cDNA clones showed that the conserved 40 nucleotides at the 5'-terminus were indispensable for replication, compared to downstream variable portion of the 5' NTR. Some of the functional mutations in the 5' NTR were tolerated in full-length cDNA clones and produced sgRNAs and virions in N. benthamiana leaves, whereas other mutations affected replication and virion formation.

Integrating Local Lesion Assays with Conventional RT-PCR for Detection of Interspecies Tospovirus Reassortants and Mixed Tospovirus Infections.

Tomato spotted wilt virus (TSWV) has historically been the major tospovirus present in North America. Recent emergence of Groundnut ringspot virus (GRSV) and Tomato chlorotic spot virus (TCSV) in Florida and the Caribbean has complicated reliable identification of tospoviruses in this region. Field symptoms of these three tospoviruses are indistinguishable in most host plants, and commercially available TSWV lateral-flow immunoassay reagents cross react with GRSV and TCSV, leading to incorrect diagnoses of GRSV or TCSV as TSWV. Reliable diagnosis of TSWV, GRSV, and TCSV is further confounded by the fact that all currently known isolates of GRSV in the United States are reassortants containing one genomic RNA segment derived from TCSV. To address these practical challenges, we developed and validated genome segment-specific primers for conventional reverse-transcription polymerase chain reaction (RT-PCR) detection of the large, medium, and small RNA segments of TSWV, GRSV, and TCSV. When used in conjunction with local lesion-passaged virus isolates, the genome segment-specific RT-PCR assays developed in this study will facilitate high-throughput screening of plant or thrips samples for interspecies reassortants in epidemiological studies and reliable identification of these three tospoviruses in mixed infections commonly observed in the field.

An Analysis of the Complete Genome Sequence and Subgenomic RNAs Reveals Unique Features of the Ampelovirus, Grapevine leafroll-associated virus 1.

Despite being the first closterovirus documented in grapevines (Vitis sp.), the molecular biology of Grapevine leafroll-associated virus 1 (GLRaV-1, genus Ampelovirus, family Closteroviridae) is still in its infancy. In this study, the complete genome sequence of two GLRaV-1 isolates was determined to be 18,731 (isolate WA-CH) and 18,946 (isolate WA-PN) nucleotides (nt). The genome of WA-CH and WA-PN isolates encodes nine putative open reading frames (ORFs) and the arrangement of these ORFs in both isolates was similar to that of Australian and Canadian isolates. In addition to two divergent copies of the coat protein (CP), the genome of GLRaV-1 isolates contain CP-homologous domain in four genes, making the virus unique among Closteroviridae members. The 5' and 3' nontranslated regions (NTRs) of WA-CH and WA-PN isolates showed differences in size and sequence composition, with 5' NTR having variable number of ∼65-nt-long repeats. Using the 5' NTR sequences, a reverse transcription-polymerase chain reaction and restriction fragment length polymorphism method was developed to distinguish GLRaV-1 variants in vineyards. Northern analysis of total RNA from GLRaV-1-infected grapevine samples revealed three subgenomic RNAs (sgRNAs), corresponding tentatively to CP, p21, and p24 ORFs, present at higher levels, with p24 sgRNA observed at relatively higher abundance than the other two sgRNAs. The 5' terminus of sgRNAs corresponding to CP, CPd1, CPd2, p21, and p24 were mapped to the virus genome and the leader sequence for these five sgRNAs determined to be 68, 27, 15, 49, and 18 nt, respectively. Taken together, this study provided a foundation for further elucidation of the comparative molecular biology of closteroviruses infecting grapevines.

An efficient and high fidelity method for amplification, cloning and sequencing of complete tospovirus genomic RNA segments.

Tospoviruses (genus Tospovirus, family Bunyaviridae) are responsible for major losses in an extensive range of crops worldwide. New species of these single-stranded, ambisense RNA viruses regularly emerge and have been shown to maintain heterogeneous populations with individual isolates having quite variable biological and virulence characteristics. Most tospovirus phylogenetic studies have focused on analysis of a single gene, most often the nucleocapsid protein gene. Complete genomic RNA segment amplification as a single fragment would facilitate more detailed analyses of genome-wide sequence variability, but obtaining such sequences for a large number of tospovirus isolates using traditional methods of amplification and cloning of small overlapping fragments is tedious, time consuming and expensive. In this study, protocols were optimized to amplify, clone and sequence full-length M- and S-RNA genome segments of Tomato spotted wilt virus and Impatiens necrotic spot virus. The strategy presented here is straightforward, scalable and offers several advantages over the previously commonplace and overlapping amplicon-based approach. Use of whole genome segments, instead of individual gene sequences or defined portions of genome segments, will facilitate a better understanding of the underlying molecular diversity of tospoviruses in mixed infections.

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.

Impacts of Grapevine Leafroll Disease on Fruit Yield and Grape and Wine Chemistry in a Wine Grape (Vitis vinifera L.) Cultivar.

Grapevine leafroll disease (GLD) is an economically important virus disease affecting wine grapes (Vitis vinifera L.), but little is known about its effect on wine chemistry and sensory composition of wines. In this study, impacts of GLD on fruit yield, berry quality and wine chemistry and sensory features were investigated in a red wine grape cultivar planted in a commercial vineyard. Own-rooted Merlot vines showing GLD symptoms and tested positive for Grapevine leafroll-associated virus 3 and adjacent non-symptomatic vines that tested negative for the virus were compared during three consecutive seasons. Number and total weight of clusters per vine were significantly less in symptomatic relative to non-symptomatic vines. In contrast to previous studies, a time-course analysis of juice from grapes harvested at different stages of berry development from symptomatic and non-symptomatic vines indicated more prominent negative impacts of GLD on total soluble solids (TSS) and berry skin anthocyanins than in juice pH and titratable acidity. Differences in TSS between grapes of symptomatic and non-symptomatic vines were more pronounced after the onset of véraison, with significantly lower concentrations of TSS in grapes from symptomatic vines throughout berry ripening until harvest. Wines made from grapes of GLD-affected vines had significantly lower alcohol, polymeric pigments, and anthocyanins compared to corresponding wines from grapes of non-symptomatic vines. Sensory descriptive analysis of 2010 wines indicated significant differences in color, aroma and astringency between wines made from grapes harvested from GLD-affected and unaffected vines. The impacts of GLD on yield and fruit and wine quality traits were variable between the seasons, with greater impacts observed during a cooler season, suggesting the influence of host plant × environment interactions on overall impacts of the disease.

Grapevine leafroll disease and associated viruses: a unique pathosystem.

Grapevine leafroll is the most complex and intriguing viral disease of grapevine (Vitis spp.). Several monopartite closteroviruses (family Closteroviridae) from grapevines have been molecularly characterized, yet their role in disease etiology is not completely resolved. Hence, these viruses are currently designated under the umbrella term of Grapevine leafroll-associated viruses (GLRaVs). This review examines our current understanding of the genetically divergent GLRaVs and highlights the emerging picture of several unique aspects of the leafroll disease pathosystem. A systems biology approach using contemporary technologies in molecular biology, -omics, and cell biology aids in exploring the comparative molecular biology of GLRaVs and deciphering the complex network of host-virus-vector interactions to bridge the gap between genomics and phenomics of leafroll disease. In addition, grapevine-infecting closteroviruses have a great potential as designer viruses to pursue functional genomics and for the rational design of novel disease intervention strategies in this agriculturally important perennial fruit crop.

Nicotiana benthamiana: Its History and Future as a Model for Plant-Pathogen Interactions.

Nicotiana benthamiana is the most widely used experimental host in plant virology, due mainly to the large number of diverse plant viruses that can successfully infect it. Addi- tionally, N. benthamiana is susceptible to a wide variety of other plant-pathogenic agents (such as bacteria, oomycetes, fungi, and so on), making this species a cornerstone of host-pathogen research, particularly in the context of innate immunity and defense signaling. Moreover, because it can be genetically transformed and regenerated with good efficiency and is amenable to facile methods for virus- induced gene silencing or transient protein expression, N. benthamiana is rapidly gaining popularity in plant biology, particularly in studies requiring protein localization, inter- action, or plant-based systems for protein expression and purification. Paradoxically, despite being an indispensable research model, little is known about the origins, genetic variation, or ecology of the N. benthamiana accessions cur- rently used by the research community. In addition to ad- dressing these latter topics, the purpose of this review is to provide information regarding sources for tools and reagents that can be used to support research in N. benthamiana. Finally, we propose that N. benthamiana is well situated to become a premier plant cell biology model, particularly for the virology community, who as a group were the first to recognize the potential of this unique Australian native.

First Report of Cucumber mosaic virus from Eggplant (Solanum melongena) in Bangladesh.

In Bangladesh, eggplant (Solanum melongena L.) is largely cultivated by subsistence farmers for domestic consumption and generating family income. During a survey of family-owned farms in April of 2014 in Barisal region of Bangladesh, we observed a farmer's field (0.25 acres) of 3-month-old eggplants with nearly 90% of plants showing mild mosaic and mottling of leaves. Symptomatic plants showed reduced growth, with nearly 50% fewer fruits than from healthy plants. Symptomatic leaves tested positive for Cucumber mosaic virus (CMV; genus Cucumovirus, family: Bromoviridae) by immunostrip diagnostic kit (Agdia, Elkhart, IN). For confirmation of the virus identity, leaf samples were pressed on FTA Plant Cards (Whatman International, Maidstone, UK) and air-dried at room temperature. For eluting total nucleic acids, four to eight disks were punched from the spotted circles of each FTA card using a Harris micropunch (2-mm diameter, Sigma-Aldrich, USA) and soaked for 1 h in 300 µl of extraction buffer (15 mM Na2CO3, 35 mM NaHCO3, 2% [w/v] PVP40, 0.2% [w/v] BSA, 0.05% [v/v] Tween 20, pH 9.6). After vortexing followed by a brief centrifugation, 10 µl of the supernatant was mixed with denaturing buffer (0.1M glycine-NaOH, pH 9.0, 50 mM NaCl, 1 mM EDTA, pH 8.0, 0.5% [v/v] Triton X-100) containing 1% ß-mercaptoethanol, incubated at 95°C for 10 min, and kept in ice until use. Denatured sample (2 µl) was subsequently used in reverse-transcription (RT)-PCR using primers CMV-RNA3F (5'-GTAGACATCTGTGACGCGA-3') and CMV-RNA3R (5'-GCGCGAAACAAGCTTCTTATC-3') previously reported (2) to amplify a 529-nucleotide (nt) fragment representing the 210-nt intergenic region and the 319-nt partial coat protein (CP) gene of the RNA 3 segment. The amplicons were cloned into pCR2.1 (Invitrogen Corp., Carlsbad, CA), and DNA isolated from four independent clones per amplicon was sequenced in both orientations. The derived sequences (GenBank Accession Nos. KM516898 to KM516901) showed close to 100% identity among themselves and 97% identity with the corresponding sequence of CMV isolate BK16 from cucumber in Thailand (FN552546). These results supported immunostrip diagnostic assays in confirming the presence of CMV in symptomatic samples of eggplants from Barisal. For additional confirmation, a second primer pair (CMV-CP-F: 5'-ATGGACAAATCTGAATCAACCAG-3' and CMV-CP-R: 5'-TCAAACTGGGAGCACCCCAGAC-3') was designed using CMV sequences from JN054635 and GU906293 to amplify the full-length CP gene from the same nucleic acid preparations used above. The approximately 657-nt amplicons, representing the full-length CP gene, were cloned, and plasmid DNA from four independent colonies per amplicon wa s sequenced as described above. The derived CP sequences (KM516902 to KM516905) shared 96 and 95% nucleotide and 98.6 and 99.5% amino acid sequence identities with corresponding sequences of CMV isolates from banana (EF178298) and eggplant (GU906293), respectively, from India. Phylogenetic analysis of CP sequences derived from this study with corresponding sequences available in GenBank indicated that CMV from eggplant in Bangladesh aligned closely with CMV subgroup 1B. CMV was previously reported in chili pepper, and tomato from Bangladesh (1) and in eggplant from Israel (4) and India (3). To our knowledge this is the first confirmed report of the occurrence of CMV subgroup 1B in eggplant in Bangladesh. Since no aphids were observed on eggplants, it is likely that CMV was introduced into the farmer's field through seedlings raised from seed carrying the virus. References: (1) A. M. Akanda et al. J. Fac. Agric., Kyushu Univ. 35:151, 1991. (2) C. De Blas et al. J. Phytopathol. 141:323, 1994. (3) S. Kumar et al. Virus Dis. 25:129, 2014. (4) E. Tanne and S. Zimmerman-Gries. Plant Dis. 64:371, 1980.

Grapevine Leafroll: A Complex Viral Disease Affecting a High-Value Fruit Crop.

Grapevine (Vitis spp.) is one of the most widely grown fruit crops in the world. It is a deciduous woody perennial vine for which the cultivation of domesticated species began approximately 6,000 to 8,000 years ago in the Near East. Grapevines are broadly classified into red- and white-berried cultivars based on their fruit skin color, although yellow, pink, crimson, dark blue, and black-berried cultivars also exist. Grapevines can be subject to attacks by many different pests and pathogens, including graft-transmissible agents such as viruses, viroids, and phytoplasmas. Among the virus and virus-like diseases, grapevine leafroll disease (GLD) is by far the most widespread and economically damaging viral disease of grapevines in many regions around the world. The global expansion of the grape and wine industry has seen a parallel increase in the incidence and economic impact of GLD. Despite the fact that GLD was recognized as a potential threat to grape production for several decades, our knowledge of the nature of the disease is still quite limited due to a variety of challenges related to the complexity of this virus disease, the association of several distinct GLD-associated viruses, and contrasting symptoms in red- and white-berried cultivars. In view of the growing significance of GLD to wine grape production worldwide, this feature article provides an overview of the state of knowledge on the biology and epidemiology of the disease and describes management strategies currently deployed in vineyards.