Grapevine leafroll-associated virus 2 (GLRaV-2) was recognized in 1984, but its nomenclature was settled only in 1995. It is one of the five viruses involved in grapevine leafroll disease. It is also associated with graft incompatibility disorders. Because of peculiar genome structure and evolutionary history, GLRaV-2 belongs to the genus Closterovirus in the family Closteroviridae. The GLRaV-2 genome is a single-stranded, positive-sense RNA of ca. 16,500 nucleotides that is presumably capped at the 5′ terminus but lacks a poly(A) tail at the 3′ end. The nine ORFs encoded by GLRaV-2 comprise three functional modules, including the replication module, the quintuple gene block module, and the module for RNA silencing suppressors. The translation product of ORF1a lacks an AlkB domain, unlike all members of the genus Ampelovirus that infect the grapevine. The genetic diversity of GLRaV-2 is very high, with six lineages that are characterized by up to 25% nucleotide divergence and different biological behavior on plant hosts. All Vitis vinifera, rootstocks, and interspecific hybrids are susceptible to GLRaV-2. The identification of GLRaV-2 in wild Vitis spp. native to the American continent supports the hypothesis that the virus originated from North America. The virus is restricted to the phloem tissue, and infected cells are characterized by a massive presence of membranous vesicles that are typical of infection by members of the genus Closterovirus. No arthropod vector is known for GLRaV-2, but the virus is graft transmissible and mechanically transmissible to some herbaceous hosts, unlike other GLRaVs. Management of GLRaV-2 is through the use of virus-tested, clean propagation materials. The recent development of infectious GLRaV-2 clones sets the foundation for studies on gene function, virus replication, pathological properties, as well as virus-host interactions.

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Grapevine leafroll-associated virus 3

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 approximatel...

https://apsjournals.apsnet.org/doi/pdf/10.1094/PDIS-08-13-0880-FE

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

Getis-Ord's hot- and cold-spot statistics as a basis for multivariate spatial clustering of orchard tree data

The aim of the present study is to prepare a nation-wide spatial database on forest cover to assess and monitor the land use changes associated with deforestation in Bangladesh. The multi-source data were interpreted to get the forest cover map of 1930, 1975, 1985, 1995, 2006 and 2014. The spatial information generated on total area under forest cover, rate of deforestation and afforestation, changes across forest types, forest canopy density, replacement land use in deforested area and deforestation hotspots. This spatial analysis has indicated that forest cover is undergoing significant negative change in area and quality. We report that forests in Bangladesh covered an area of 23,140 km2 in 1930 which has decreased to 14,086 km2 in 2014, a net loss of 9054 km2 (39.1%) in eight decades. Analysis of annual rate of gross deforestation for the recent period indicates 0.77% during 2006–2014. During the past eight decades, semi-evergreen forests show loss of 56.4% of forest cover followed by moist deciduous forests (51.5%), dry deciduous forests (43.1%) and mangroves (6.5%). The loss of 23.5% of dense forest cover was found from 1975 to 2014. Dense semi-evergreen forests shows more negative change (36.9%) followed by dense moist deciduous forest (32.7%) from 1975 to 2014. Annual rate of deforestation is higher in dense forests compared to open forests from 2006 to 2014 and indicates increased threat due to anthropogenic pressures. The spatial analysis of forest cover change in mangroves has shown a lower rate of deforestation. Most of the forest conversions have led to the degradation of forests to scrub and transition to agriculture and plantation. The study has identified the ‘deforestation hotspots’ can help in strategic planning for conservation and management of forest resources.

Development of national database on long-term deforestation (1930–2014) in Bangladesh

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

The vine mealybug, Planococcus ficus (Signoret) (Hemiptera: Pseudococcidae), is a major pest of vineyards. Here, we tested the efficacy of the mating disruption method against the pest when applied during one or two successive years in high and low infestation levels. Following 1 year of treatment, at low initial infestation levels a shutdown of pheromone traps was observed, along with a significant reduction in infested vines. With initially high infestation levels, a gradual reduction in infested vines was observed, with a trap shutdown seen only after the second year of pheromone application. We discuss the implications of the male mating disruption method for this pest in which the wingless females are aggregated with limited movement among vines, offering multiple mating opportunities for the flying male.

Mating disruption method against the vine mealybug, Planococcus ficus: effect of sequential treatment on infested vines

Background and Aims

Grapevine leafroll disease (GLD) is one of the most widespread viral diseases of grapevine. In the present study, we suggest a methodology that combines real multiyear GLD spatial infection data and simulations of different management strategies to study their impact on GLD spread.



Methods and Results

We used real multiyear data on spatial infection of GLD to assess the infection risk to vines adjacent to infected vines. Directly adjacent vines were at significantly higher risk for infection in subsequent years than distant vines. Nevertheless, we found no difference in the absolute number of newly infected vines yearly between the directly adjacent and distant vines, indicating that GLD spread occurs in adjacent vines and randomly throughout the vineyard. We used the real multiyear GLD spatial infection data to simulate control strategies: uprooting; uprooting supplemented with insecticide treatment of neighbouring vines; and treatment of neighbouring vines with no uprooting and to study their impact on GLD spread. Uprooting with and without supplemental treatment to neighbouring vines significantly decelerated infection spread over a 7-year period (from 30 to 8.6%). The combined treatment, however, of infected and neighbouring vines yielded a lower infection level with less uprooting events compared with uprooting alone.



Conclusion

Despite the risk of GLD spread to distant vines, the significantly higher risk of directly adjacent vines and their known location make them more relevant to management strategies for the control of disease dissemination.



Significance of the Study

The combination of simulations with real data revealed additional information on GLD spread under different management strategies that deviated from the expected dissemination process.

Potential efficiency of grapevine leafroll disease management strategies using simulation and real spatio-temporal disease infection data

Given a set of geo-referenced data points, the Getis–Ord Gi* statistic identifies hot-spots of points with values higher in magnitude than one might expect by a random chance. This tool works by looking at each data feature and its neighboring features in comparison to the overall spatial distribution of the phenomenon explored. If the difference between the local sum for a feature and its neighbors is highly larger than expected (the overall sum) a hot-spot is accepted. Leaf-roll virus (LRV) in vineyards appears in clusters which expand from year to year when no pest control is carried out. Exploring the spatio-temporal expansion of hot-spots of the LRV is limited with the Gi* statistics since relative hot-spots are accepted according to the infestation level of a specific year. A modified Gi* was developed which identifies year-to-year hot-spots which are relative to a year of reference. LRV symptoms were mapped yearly in a vineyard from 2005 to 2010. The Gi* indicated for a northern hot-spot only in 2007 and a southern one in 2009. Using the modified Gi* with 2005 as a year of reference, the northern and the southern clusters were identified in 2006 and 2007, respectively.

/pdf/modified-hot-spot-analysis-for-spatio-temporalanalysis-a-42gwblp0wu.pdf

Modified Hot-Spot analysis for spatio-temporalanalysis: a case study of the leaf-roll virus expansion in vineyards

The host plant Vitex agnus-castus attractiveness to the “stolbur” phytoplasma vector Hyalesthes obsoletus was exploited to study application methods of trap plants in order to reduce yellows disease incidence in vineyards. Following the introduction of the trap plants in vineyards, infestation level was reduced. The effect on plot infestation level diminishes with distance from trap plants and varies depending on the trap plant biomass. There is also indication of trap plant effect joined with wind direction. The grapevine yellows disease can be controlled in Israel conditions by means of trap plants that lure the vector.

Trap plants reduces grapevine yellows disease incidence in commercial vineyards

Grapevine leafroll disease (GLD) is one of the most widespread viral diseases of grapevines. A risk assessment study of healthy vines is presented using real multi-year GLD spatial infestation data. Spatial distribution and dynamics of GLD were studied in a commercial vineyard from 2005 to 2011. These GLD spatio-temporal spread studies have shown that following the first few years of random spatial distribution of the disease, it spreads mainly along rows. The work compares the risks of healthy vines adjacent to infected vines in the same row and in adjacent rows. In each year, healthy vines were classified into groups according to their distance from infested vines. In the subsequent years, they were examined for infestation to assess their risk. It was found that infestation risk decreases with the distance from infested vines. Directly neighboring vines were found at significantly higher risk (14.8%) than vines at a distance greater than 3 m from infected vines. The risk of the latter vines was half of that from the directly neighboring vines (7%). The identification of vines at high risk of infestation according to their distance from infected vines may be useful in developing strategies for potential site-specific controls for preventing GLD spread.

Tamar Sokolsky

Papers

Mating disruption method against the vine mealybug, Planococcus ficus: effect of sequential treatment on infested vines

Potential efficiency of grapevine leafroll disease management strategies using simulation and real spatio-temporal disease infection data

Modified Hot-Spot analysis for spatio-temporalanalysis: a case study of the leaf-roll virus expansion in vineyards

Trap plants reduces grapevine yellows disease incidence in commercial vineyards

Risk assessment of grapevine leafroll disease for developing future site-specific disease spread control tactics and strategies