Grapevine Leafroll Disease Research Articles

A Synoptic Analysis of the Temporal and Spatial Aspects of Grapevine Leafroll Disease in a Historic Napa Vineyard and Experimental Vine Blocks.

Five Grapevine leafroll-associated virus 3 (GLRaV-3) epidemics were analyzed utilizing a standardized approach to robustly characterize the temporal and spatial parameters. Published data included in the analysis are from Spain, New Zealand, and Napa Valley, CA together with new data from a historic vineyard in Napa Valley, CA. Linear regression analyses of logit-transformed incidence data indicated a maximum average increase of 11% per year in disease incidence, with considerable variation among locations. Spatial analyses, including distribution fitting, examination of the effective sample size, and evaluation of the parameters of the binary power law fitted to variance data for disease incidence, indicated a high degree of consistency among the data sets. In all cases, except at very low disease incidence, a high degree of spatial aggregation was noted, with evidence that the degree of aggregation varied as a function of mean disease incidence. The polyetic dynamics of disease follow a logistic-like pattern over multiple seasons, consistent with limitation by inoculum availability (infected vines) at low incidence and limitation by disease-free vines at high incidence.

CHARACTERIZATION OF GRAPEVINE LEAFROLL-ASSOCIATED VIRUS 4 FROM INDIAN VINEYARDS

In a 2013-15 survey, typical symptoms of grapevine leafroll disease were observed in vineyards of Western and North-Eastern India. Twelve grapevine cultivars were infected with Grapevine leafroll-associated virus 4 (GLRaV-4), as shown by ELISA. The coat protein (CP), heat shock protein 70 homologue (HSP70h) and p23 genes of GLRaV-4 isolates from India were characterized by RT-PCR and sequencing. A phylogenetic analysis of the CP gene showed that the Indian isolates clustered with GLRaV-4 isolates Y252-IL (AM162279) from Israel, Y253-TK (AM176759) from Turkey, and LR106 (FJ467503) from USA with a maximum identity of 98% at the amino acid level. Sequences analysis revealed intra- and inter-species recombination events within CP and p23 genes of GLRaV-4 isolates. Indian isolates GRP-G (KT759152) and GDR-I (KT759153) diverged from other GLRaV-4 isolates in their p23 gene. This is the first report of the occurrence of GLRaV-4 in Indian vineyards and of recombination in the GLRaV-4 genome.

Differential expression of miRNAs and associated gene targets in grapevine leafroll-associated virus 3-infected plants.

MicroRNAs (miRNAs) are a class of endogenous small non-coding RNAs (sRNA) that play an essential role in the regulation of target mRNAs expressed during plant development and in response to stress. MicroRNA expression profiling has helped to identify miRNAs that regulate a range of processes, including the plant's defence response to pathogens. In this study, differential miRNA expression in own-rooted Vitis vinifera cv. Cabernet Sauvignon plants infected with grapevine leafroll-associated virus 3 was investigated with microarrays and next-generation sequencing (NGS) of sRNA and mRNA. These high-throughput approaches identified several differentially expressed miRNAs. Four miRNAs, identified by both approaches, were validated by stemloop RT-PCRs. Three of the predicted targets of the differentially expressed miRNAs were also differentially expressed in the transcriptome data of infected plants, and were validated by RT-qPCR. Identification of these miRNAs and their targets can lead to a better understanding of host-pathogen interactions involved in grapevine leafroll disease and the identification of possible targets for virus resistance.

Remote hyperspectral imaging of grapevine leafroll-associated virus 3 in cabernet sauvignon vineyards

Grapevine leafroll disease (GLD) is considered to be one of the most economically destructive viral diseases of grapevines worldwide, resulting in reduced vine vigor, yield reductions, and poor fruit quality. Five pathogens (grapevine leafroll-associated viruses) are recognized as causal agents of this disease, of which Grapevine leafroll-associated virus 3 (GLRaV-3) is the most common. Although there is no cure for the disease, management strategies (including vigilant removal of infected vines) can drastically limit its spread and economic impact. Comprehensive mapping (total population sampling) of disease presence on the ground is cumbersome and cost prohibitive in many situations. In addition, the practice of identifying diseased vines requires individuals to be highly trained to recognize symptoms. Compared to more traditional detection methods, airborne hyperspectral imaging offers a potentially valuable alternative for monitoring the disease that is cost effective, reliable and automatable. This study tests the use of hyperspectral imaging to aid in the management of GLD.Over the span of two years we monitored five Cabernet Sauvignon vineyards: ground surveys recorded the incidence of visual symptoms of disease in the field during the same months in which hyperspectral maps recorded disease incidence from the air. A customized Geographic Information System (GIS) methodology was developed to compare the visual symptoms to the results of the hyperspectral imaging technique. For a select number of vines, disease incidence was then confirmed by laboratory assays. On average, detection sensitivity was 94.1%, with a range of 88% to greater than 99% per vineyard. Various vineyard-specific factors appear to compromise detection sensitivity. Overall, our results show that remote hyperspectral imaging of GLRaV-3 infected Cabernet Sauvignon vineyards can be a useful and cost-effective approach to mapping diseased vines. Future studies should focus on the use of this tool for detecting GLRaV-3 in other grape varieties, as well as other grapevine pathogens.

Physiological response of grapevine Vitis vinifera L. to grapevine leafroll associated viruses (GLRaV-1 and GLRaV-1 + GLRaV-3)

Grapevine leafroll disease is one of the most severe viral diseases of grapevine caused by Grapevine leafroll-associated viruses (GLRaVs). Physiological processes were monitored on grapevines with single (GLRaV-1) and mixed (GLRaV-1 and GLRaV -3) viral infection under greenhouse conditions from June to September, in vegetation period 2014. In the mid of the season (July) negative effects of the virus infections on physiological processes were more severe in mixed than in single infection. The net-photosynthesis (Pn) of the leaves infected with GLRaV-1 and GLRaV-3 reached only a half of the Pn in GLRaV-1 infected grapevines. Similar reduction was found for stomatal conductance, transpiration and parameters related to photochemical efficiency (electron transport rate).

No evidence of transmission of grapevine leafroll-associated viruses by phylloxera (Daktulosphaira vitifoliae)

Grapevine leafroll disease is associated with several species of phloem-limited grapevine leafroll-associated viruses (GLRaV), some of which are transmitted by mealybugs and scale insects. The grape phylloxera, Daktulosphaira vitifoliae (Fitch) Biotype A (Hemiptera: Phylloxeridae), is a common vineyard pest that feeds on the phloem of vine roots. There is concern that these insects may transmit one or more GLRaV species, particularly GLRaV-2, a species in the genus Closterovirus. A field survey was performed in vineyards with a high incidence of grapevine leafroll disease and D. vitifoliae was assessed for acquisition of GLRaV. In greenhouse experiments, the ability of D. vitifoliae to transmit GLRaV from infected root sections or vines to co-planted virus-free recipient vines was tested. There were no GLRaV-positive D. vitifoliae in the field survey, nor did D. vitifoliae transmit GLRaV-1, −2, −3, or -4LV in greenhouse transmission experiments. Some insects tested positive for GLRaV after feeding on infected source vines in the greenhouse, however there was no evidence of virus transmission to healthy plants. These findings, in combination with the sedentary behaviour of the soil biotype of D. vitifoliae, make it unlikely that D. vitifoliae is a vector of any GLRaV.

Transmission of Grapevine Leafroll-associated Virus 3 by Vine Mealybug, Planococcus ficus (Signoret), to Grapevines Treated with Imidacloprid

Grapevine leafroll disease is widely accepted to be the most damaging grapevine virus disease in South Africa. The current industry strategy to limit leafroll infection in new vineyards includes treating newly planted grapevines with a systemic insecticide like imidacloprid and rogueing all grapevines that exhibit leafroll symptoms. A tendency by some producers to eschew rogueing and rely solely on imidacloprid applications to control vine mealybug and so protect new vineyards from leafroll infection gave rise to this study. Two bioassays were conducted to determine if Planococcus ficus (Signoret) nymphs can transmit grapevine leafroll-associated virus 3 (GLRaV-3) to potted indicator grapevines treated with imidacloprid applied through the soil five months before exposure to viruliferous mealybugs. Ten of 21 leafroll-free grapevines treated with imidacloprid tested positive for GLRaV-3 seven to eight weeks after being exposed to viruliferous first- and second-instar P. ficus nymphs. This means that the systemic applications of imidacloprid to newly planted, virus-free vineyards will not necessarily protect the vines from GLRaV-3 if they become infested by viruliferous vine mealybugs, although the insecticide provides effective mealybug control and helps to prevent the secondary spread of leafroll infection in these vineyards. To control the spread of leafroll virus to newly planted, leafroll-free vineyards, all grapevines that serve as sources of infection should be removed. Where this is not feasible, vectors should be monitored and controlled rigorously in infested and disease-free vineyards alike, while all infected grapevines should be removed from new vineyards as they begin to develop leafroll symptoms.

Transmission ofGrapevine virus AandGrapevine leafroll-associated virus 1and3byHeliococcus bohemicus(Hemiptera: Pseudococcidae) Nymphs From Plants With Mixed Infections

Mealybugs (Hemiptera: Pseudococcidae) represent a serious threat for viticulture as vectors of phloem-restricted viruses associated with the grapevine rugose wood and leafroll diseases. Heliococcus bohemicus (Šulc) is known to be involved in the spread of these two viral diseases, being a vector of the Grapevine virus A (GVA) and the Grapevine leafroll-associated virus 1 and 3 (GLRaV-1 and GLRaV-3). This study investigated the acquisition and transmission efficiency of H. bohemicus fed on mixed-infected plants. Nymphs were field-collected onto GVA, GLRaV-1, and GLRaV-3 multiple-infected grapevines in two vineyards in North-Western Italy, and were used in transmission experiments under controlled conditions. Even if most of the collected nymphs were positive to at least one virus, transmission occurred only to a low number of test grapevines. The transmission frequency of GLRaV-3 was the highest, whereas GVA was transmitted to few test plants. The transmission of multiple viruses occurred at low rates, and nymphs that acquired all the three viruses then failed to transmit them together. Statistical analyses showed that the three viruses were independently acquired and transmitted by H. bohemicus and neither synergistic nor antagonistic interactions occurred among them. GVA and GLRaVs transmission efficiencies by H. bohemicus were lower than those reported for other mealybug vectors. This finding is consistent with the slow spread of leafroll and rugose wood diseases observed in Northern Italy, where H. bohemicus is the predominant vector species.

Ferrisia gilli(Hemiptera: Pseudococcidae) Transmits Grapevine Leafroll-Associated Viruses

Several mealybug species are vectors of grapevine leafroll-associated viruses (GLRaV), which cause the economically important grapevine leafroll disease in grape-producing regions worldwide. The mealybug Ferrisia gilli Gullan is a new pest of grapevines in El Dorado County, located in the Sierra Foothill wine-growing region of California. GLRaV species 1, 2, 3, and 4LV have been detected in vineyards with symptomatic vines in the Sierra Foothills. We conducted controlled virus acquisition and transmission experiments using source vine accessions infected with different combinations of GLRaV. We determined that F. gilli acquired GLRaV 1, 2, 3, and 4LV, and transmitted GLRaV-3 and GLRaV-4LV to uninfected recipient vines. Like numerous other mealybug species, in addition to causing direct damage to vines, F. gilli poses a threat to the grape industry as a vector of economically damaging viruses.

Disease progression of vector-mediated Grapevine leafroll-associated virus 3 infection of mature plants under commercial vineyard conditions

Grapevine leafroll-associated virus 3 (GLRaV-3) is associated with the economically damaging grapevine leafroll disease, and is transmitted in a semi-persistent manner by several mealybug species. We performed the first controlled field study of vector-mediated inoculations with GLRaV-3 in a commercial vineyard with previously asymptomatic vines, and monitored the vines during four growing seasons. We then compared the outcome of vector-mediated inoculations in the field study to an analogous laboratory study. In the vineyard, about half of all inoculated plants became infected with GLRaV-3, fewer than in the controlled laboratory inoculations. Mealybugs had lower settling and feeding success in the field than in the laboratory inoculations. Our study suggests that laboratory studies may overestimate transmission efficiency. All successfully inoculated vineyard plants first became symptomatic one growing season after inoculations, and berry quality declined within one year after inoculations. Vineyard plants were effective virus sources one year after inoculations. Our findings generally indicate that newly symptomatic vines in commercial vineyards probably became infected during the previous growing season, and a decline in berry quality can be expected during the same year in which symptoms appear.

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.

Spatio-temporal association of GLRaV-3-infected grapevines, and effect of insecticidal treatments on mealybug populations in Virginia vineyards

Grapevine leafroll disease (GLD) is caused by a number of viruses in the grapevine leafroll-associated virus complex (GLRaVs). GLRaV-3 is the most commonly found GLRaV and is transmitted by mealybugs (Hemiptera: Pseudococcidae) and soft scale insects (Hemiptera: Coccidae). A series of investigations were conducted to understand spatio-temporal patterns of GLRaV-3 and mealybugs, and to examine management strategies of mealybugs under the environmental conditions of Virginia, USA. During the study, a rapid increase (185 % per year) of GLRaV-3 positive vines was observed at an experimental vineyard. Spatial Analysis by Distance IndicEs (SADIE) indicated a mix of aggregated, random, and uniform distributions of GLRaV-3 within six surveyed vineyards, and a temporal association of GLRaV-3-positive vines over three years at the experimental vineyard. Results from a field experiment in 2009–2011 showed the effect of a delayed dormant application of acetamiprid (Assail, 0.182 L/ha) to be not significantly differing in mealybug abundance from the unsprayed check in 2010 and 2011. Moreover, an application of the contact insecticide beta-cyfluthrin (Baythroid XL, 0.219 L/ha) resulted in significantly higher numbers of mealybugs counted in 2011. This study also demonstrated that GLRaV-3 was spread from mature vines to newly planted sentinel vines during the first growing season, with no apparent effect of prevailing wind direction. Results from another insecticide trial conducted in 2010–2011 demonstrated that both dinotefuran (Scorpion, 0.292 L/ha) and spirotetramat (Movento, 0.439 L/ha) treatments significantly reduced mealybug counts when mealybug populations were high, but only spirotetramat significantly reduced mealybug counts when mealybug populations were low.

The effect of grapevine leafroll plus yellow speckle disease on annual growth, yield and quality of grapes from Cabernet Franc under two pruning systems

The effects of two combinations of grapevine leafroll plus yellow speckle disease in two high-yielding Sultana selections (H4 and H5) on the performance of Cabernet Franc under two pruning methods were determined over 6 years. When averaged over the 6 years, H5 and H4 reduced the weight of annual growth by 21%and15 %, decreased the yield of fresh fruit by 9 % and 6 %, and depressed the sugar concentration of juice by 0.6 and 0.3 °Brix respectively. The titratable acidity and the pH of juice were slightly affected in some years. The number of inflorescences and mean berry weight were not affected by either virus source. When compared with spur pruning and averaged over the 4 years, cane-pruned vines produced less annual growth (21 % ), progressively less fresh fruit (16 % ), and had lighter berries (9 % ), but effects on the numbers of inflorescences and sugar content were inconsistent between years; the acidity and pH of juice were not affected. Canepruned vines had obviously inferior and more variable fruit-set. However, no visible differences in fruit-set due to the virus sources within each pruning method were detected. There was evidence of a low incidence of natural spread of yellow speckle, but not of leafroll. Holzproduktion sowie Traubenertrag und -qualitat von Cabernet Franc bei kombinierter Einwirkung von Leafroll und Yellow speckle disease in Verbindung mit zwei verschiedenen Anschnittsystemen Zwei Kombinationen von Leafroll mit Yellow speckle disease wurden von den beiden ertragsstarken Sultana-Klonen H4 und H5 auf die Sorte Cabernet Franc, die auf Zapfen und auf Bogreben angeschnitten war, ubertragen. Der Einflus der Infektion auf die Leistungsfahigkeit dieser Sorte wurde uber einen Zeitraum von 6 Jahren verfolgt. Im Durchschnitt der 6 Jahre war nach der Krankheitsubertragung von den Infektionsquellen H5 und H4 das Gewicht des jahrlich produzierten Holzes um 21 bzw. 15 %, der Traubenertrag (Frischgewicht} um 9 bzw. 6 % und die Mostzuckerkonzentration um 0,6 bzw. 0,3 ° Bri.« verringert. In einigen Jahren waren auch die titrierbare Saure und das pH des Mostes leicht verandert. Die Anzahl der Infloreszenzen und das mittlere Beerengewicht wurden durch keine der beiden Viruskombinationen beeinflust. Im Vergleich zu den auf Zapfen geschnittenen Reben zeigte Cabernet Franc bei Bogrebenschnitt im Mittel von 4 Jahren einen verringerten jahrlichen Holzzuwachs (21 %), stetig abnehmenden Traubenertrag (16 %, bezogen auf Frischgewicht} und leichtere Beeren (9 %); die Anzahl der Infloreszenzen und der Zuckergehalt wurden durch den Anschnitt von Jahr zu Jahr uneinheitlich beeinflust; ein Einflus auf Saure und pH des Mostes lag nicht vor. Auf Bogen geschnittene Reben hatten einen deutlich erniedrigten und starker schwankenden Beerenansatz. Innerhalb eines Schnittsystems wirkten sich die unterschiedlichen Virusherkunfte jedoch nicht merklich auf den Beerenansatz aus. Es wurde eine langsame naturliche Ausbreitung von Yellow speckle, aber nicht von Leafroll nachgewiesen.

Detection of grapevine leafroll disease based on 11-index imagery and ant colony clustering algorithm

Grapevine leafroll disease (GLD) is a virus disease that quickly propagates through vineyards under appropriate weather conditions and can reduce grape production worldwide by nearly 60 %. Therefore, the accurate diagnosis and reliable evaluation of GLD distribution, particularly at the early stage of GLD infection, is important to prevent the spread of this disease. This study applied the ant colony clustering algorithm (ACCA) to detect GLD spectral anomalies on 4 GLD-infected vineyards according to multi-spectral imagery for precision disease management. GLD was classified into three stages: GLD1, GLD2 and GLD3 according to its infection severity. An 11-index feature vector and its stacked image were generated to enhance the spectral differences and spectral discrimination between diseased and healthy grapevines. ACCA was then designed to solve the fuzziness of the multi-spectral image for GLD-infected grapevines and successfully identify GLD from healthy grapevines. Finally, a field survey with 49 samples and pixel purity index technology were applied to validate the effectiveness, efficiency and accuracy of ACCA. Field results indicated that an early stage of the GLD infection (GLD1) could be successfully discriminated from GLD2-, GLD3- and non-infected grapevines. The classification accuracies of non-, GLD1-, GLD2- and GLD3-infected grapevines were 94.4, 75, 84.6 and 83.3 %, respectively. Hence, the method based on an 11-index image and ACCA may significantly detect GLD at an early stage from healthy grapevines for precision disease management at the field level.

Molecular characterization of a grapevine leafroll-associated virus 4 from Slovenian vineyards.

During a survey conducted in vineyards in Slovenia, variety of grapevine leafroll disease symptoms were observed. Mixed infection with grapevine leafroll-associated viruses 3 and 4 (GLRaV-3, -4) in two grapevines from a vineyard in south-western part of Slovenia was confirmed by DAS-ELISA in 2010. The 3'final 1769 nucleotides of the Slovenian GLRaV-4 isolate were assembled from amplicons obtained by IC RT-PCR. The complete coat protein (CP) and p23 gene sequences were compared with other GLRaV-4 sequences from GenBank. Results showed that CP and p23 amino acid sequences of Slovenian variant (055-SI) are 88% and 85%, respectively, identical to corresponding genes of reference sequence GLRaV-4 LR106 (GenBank Acc. No. FJ467503). Phylogenetic analyses show that Slovenian variant clusters together with other corresponding strains of GLRaV-4. The sequencing results show great variability of the N-terminal part of the CP sequence indicating that this part of the genome is not suitable for molecular detection of the virus. To our knowledge this is also the first report of GLRaV-4 in Slovenian vineyards.

Relative Prevalence of Grapevine Leafroll-Associated Virus Species in Wine Grape-Growing Regions of California.

Some diseases manifest as one characteristic set of symptoms to the host, but can be caused by multiple pathogens. Control treatments based on plant symptoms can make it difficult to effectively manage such diseases, as the biology of the underlying pathogens can vary. Grapevine leafroll disease affects grapes worldwide, and is associated with several viral species in the family Closteroviridae. Whereas some of the viruses associated with this disease are transmitted by insect vectors, others are only graft-transmissible. In three regions of California, we surveyed vineyards containing diseased vines and screened symptomatic plants for all known viral species associated with grapevine leafroll disease. Relative incidence of each virus species differed among the three regions regions, particularly in relation to species with known vectors compared with those only known to be graft-transmitted. In one region, the pathogen population was dominated by species not known to have an insect vector. In contrast, populations in the other surveyed regions were dominated by virus species that are vector-transmissible. Our survey did not detect viruses associated with grapevine leafroll disease at some sites with characteristic disease symptoms. This could be explained either by undescribed genetic diversity among these viruses that prevented detection with available molecular tools at the time the survey was performed, or a misidentification of visual symptoms that may have had other underlying causes. Based on the differences in relative prevalence of each virus species among regions and among vineyards within regions, we expect that region and site-specific management strategies are needed for effective disease control.

Comparison of rapid detection assays for grapevine leafroll disease associated closteroviruses

Three rapid detection assays (ELISA, dsRNA analysis and ISEM) were compared for their sensitivity, specificity, and simplicity in the detection of grapevine leafroll associated closteroviruses (GLRaV). Each was found to have advantages and disadvantages for routine testing. ELISA is sensitive and easy to use, but different antisera are needed to detect different GLRaV types. Because mixing or blending of antisera can produce good results in a single ELISA test, each antiserum does not need to be used separately unless it is important to determine the type of GLRaV present. DsRNA analysis can detect all the types of GLRaV tested but has a relatively low sensitivity and is labor intensive, which makes it unsuitable for testing large numbers of samples. Furthermore, dsRNA does not give unequivocal diagnosis of GLRaV infections. ISEM is sensitive and rapid. However, like ELISA, this technique requires an antiserum to each GLRaV type tested and an electron microscopy. Our recommendation is that ELISA should be used with multiple antisera for large scale testing programs. Samples for which ELISA results are inconclusive should be retested with ISEM and/or dsRNA. When the disease status of an individual sample must be determined conclusively, a few grams of tissue should be processed to concentrate the virus and then subjected to ELISA and examination by electron microscopy with negative staining. A dsRNA analysis should be carried out as well.

Biological, Serological, and Molecular Characterization of a Highly Divergent Strain of Grapevine leafroll-associated virus 4 Causing Grapevine Leafroll Disease.

The complete genome sequence of a highly divergent strain of Grapevine leafroll-associated virus 4 (GLRaV-4) was determined using 454 pyrosequencing technology. This virus, designated GLRaV-4 Ob, was detected in Vitis vinifera 'Otcha bala' from our grapevine virus collection at Agroscope. The GLRaV-4 Ob genome length and organization share similarities with members of subgroup II in the genus Ampelovirus (family Closteroviridae). Otcha bala was graft-inoculated onto indicator plants of cultivar Gamay to evaluate the biological properties of this new strain, and typical leafroll symptoms were induced. A monoclonal antibody for the rapid detection of GLRaV-4 Ob by enzyme-linked immunosorbent assay is available, thus facilitating large-scale diagnostics of this virus. Based on the relatively small size of the coat protein, the reduced amino acid identity and the distinct serological properties, our study clearly shows that GLRaV-4 Ob is a divergent strain of GLRaV-4. Furthermore, molecular and serological data revealed that the AA42 accession from which GLRaV-7 was originally reported is in fact co-infected with GLRaV-4 Ob and GLRaV-7. This finding challenges the idea that GLRaV-7 is a leafroll-causing agent.

Retracted Article - The Economic Benefits from Virus Screening: A Case Study of Grapevine Leafroll in the North Coast of California

We the authors retract the article "The economic benefits from virus screening: A case study of grapevine leafroll in the North Coast of California," from the American Journal of Enology and Viticulture (AJEV) because we became aware of errors in the article that resulted from a coding error in a formula that was used to calculate losses from the grapevine leafroll disease. While the overall message of the paper is unchanged, the estimates of the benefits from virus screening are significantly smaller when the correct formula is used. Corrections were necessary in the Abstract, Introduction, Results and Discussion, and Conclusion sections of the article, as well as in Tables 3-7. This article was originally published on May 1, 2015 in Volume 66, Issue 2 of AJEV. We alerted the AJEV editors and editorial staff to these errors on July 16, 2018, and have published a new manuscript in the April 2019 (70:2) AJEV issue that incorporates the necessary corrections. The authors regret the previous errors and apologize to our readers. Retracted August 2018

Genetic diversity and recombination analysis of grapevine leafroll-associated virus 1 from China.

Grapevine leafroll-associated virus 1 (GLRaV-1) is one of the causal agents of grapevine leafroll disease (GLD). To investigate the prevalence and genetic variation of GLRaV-1 in China, 132 grapevine samples from 14 Chinese provinces and regions were tested using reverse transcription PCR (RT-PCR) and reverse transcription nested PCR (RT-nPCR). The samples included symptomatic and asymptomatic cultivars, and 36.4% of them tested positive for GLRaV-1. 'Beida' samples, previously identified as virus-free rootstocks, were also found to be infected with GLRaV-1 with an incidence of 40 . GLRaV-1 coat protein (CP) genes and heat-shock protein 70 (HSP70) genes from 43 GLRaV-1 isolates were selected and sequenced. Phylogenetic analysis of global CP and HSP70 gene sequences showed that all variants belonged to eight and seven groups, respectively. For CP gene sequence variants, group 4 was a new group that included only Chinese isolates. The results also showed that natural selection, rather than random processes, led to the evolution of variants belonging to CP gene sequence variants in group 2 and group 8. Furthermore, three new recombination events were identified in the GLRaV-1 CP gene population. This is the first report on the genetic variation of GLRaV-1 isolates in China, and this study will benefit grape clean-plant programs in China.