Mealybug transmission of Grapevine leafroll viruses: an analysis of virus-vector specificity.

Department of Entomology, National Taiwan University, Taipei 106, Taiwan.
Phytopathology (Impact Factor: 2.75). 08/2010; 100(8):830-4. DOI: 10.1094/PHYTO-100-8-0830
Source: PubMed

ABSTRACT To understand ecological factors mediating the spread of insect-borne plant pathogens, vector species for these pathogens need to be identified. Grapevine leafroll disease is caused by a complex of phylogenetically related closteroviruses, some of which are transmitted by insect vectors; however, the specificities of these complex virus-vector interactions are poorly understood thus far. Through biological assays and phylogenetic analyses, we studied the role of vector-pathogen specificity in the transmission of several grapevine leafroll-associated viruses (GLRaVs) by their mealybug vectors. Using plants with multiple virus infections, several virus species were screened for vector transmission by the mealybug species Planococcus ficus and Pseudococcus longispinus. We report that two GLRaVs (-4 and -9), for which no vector transmission evidence was available, are mealybug-borne. The analyses performed indicated no evidence of mealybug-GLRaV specificity; for example, different vector species transmitted GLRaV-3 and one vector species, Planococcus ficus, transmitted five GLRaVs. Based on available data, there is no compelling evidence of vector-virus specificity in the mealybug transmission of GLRaVs. However, more studies aimed at increasing the number of mealybug species tested as vectors of different GLRaVs are necessary. This is especially important given the increasing importance of grapevine leafroll disease spread by mealybugs in vineyards worldwide.


Available from: Kent Daane, Jun 14, 2015
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    ABSTRACT: The Grape Mealybug (Pseudococcus maritimus) is a known vector of grapevine leafroll associated viruses (GLRaVs) and is implicated in the potential spread of these viruses within wine grape vineyards (Vitis vinifera cv.). Grapevine leafroll disease, caused by GLRaVs, is the most devastating viral disease of wine grapes worldwide. However, in Concord juice grapes (Vitis labrusca), GLRaVs appear to produce latent infections, therefore little attention has been paid to the role of mealybugs as vectors in Concord vineyards. In Washington State, the most common GLRaV is GLRaV-3 and has been confirmed in Concord vineyards. In this study, grape mealybugs were reared on Pixie cv. grapes. First instar crawlers were allowed to feed on an infected grapevine for three days and were then transferred to virus free Concord vines. Concord vines were tested at intervals of two weeks, one month, three months, and six months. To detect the virus, plant material was tested using RT-PCR and real-time PCR techniques using primers for various genes for GLRaV-3. When tested for Hsp70, all Concord samples tested negative. When tested for the RdRp gene, all Concord samples tested positive for the presence of GLRaV-3. Samples were also tested for CP, p20a, and p20b. No virus was detected when tested for p20a or CP but two samples tested positive for p20b. Based on these preliminary data, it appears that the grape mealybug can vector GLRaV-3 in Concord juice grapes.
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    ABSTRACT: A statewide survey of commercial vineyards in Virginia (VA), USA was conducted in 2009–2011 seasons to examine the occurences of Grapevine leafroll-associated virus-2 (GLRaV-2), Grapevine leafroll-associated virus-3 (GLRaV-3), Grapevine fleck virus (GFkV), and mealybugs. Out of 415 samples (comprising 41 wine grape cultivars) from 77 locations (vineyards), GLRaV-2, GLRaV-3 and GFkV were detected by RT-PCR in 8, 25, and 1 %, respectively, and 64 % of vineyards were positive for at least one of the three viruses. Samples from 100 wild Vitis sp. tested negative for the three viruses. Both the grape (Pseudococcus maritimus) and Gill’s (Ferrisia gilli) mealybug were found in VA vineyards. Although regional effect was not significant (P > 0.05), examination of variance showed higher variability of GLRaV-3 incidence at cultivar scale within a vineyard than at a smaller spatial scale (i.e., at sampling site). In addition, the probability of finding a GLRaV-3-infected vine was higher in the presence of mealybugs (P P Ferrisia gilli, GLRaV-2, GLRaV-3, and GFkV in VA vineyards.
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    ABSTRACT: New insights into the genetic structure and variability of grapevine leafroll-associated viruses (GLRaVs) gained through worldwide efforts in the last decade or so, and the production and use of new sets of serological reagents, have provided the solid foundation on which the present revision of the taxonomic structure of the family Closteroviridae, and the genus Ampelovirus in particular, is based. A comparative examination of the amino acid sequence divergence of three taxonomically relevant genes [RNA-dependent RNA polymerase (polymerase), heat shock protein 70 homologue (HSP70h) and coat protein (CP)] disclosed a difference among Grapevine leafroll-associated virus 4 (GLRaV-4), -5, -6 and -9 and a group of more recently described viruses (GLRaV-Pr, GLRaV-De and GLRaV-Car) below the 25% limit recently set by the International Committee on Taxonomy of Viruses (ICTV) as a discriminating criterion for the identification of species in the family Closteroviridae. This, plus the recognition that GLRaV-4, -5, -6 and -9 are serologically related, have similar biological and epidemiological traits, and that these viruses and GLRaV-Pr, GLRaV-De, GLRaV-Car have a genome with the same structure and size, supports the notion that they are all genetically divergent variants of a single species, GLRaV-4. The genus Ampelovirus is split into two subgroups designated I and II in recognition of the wide difference in the size and structure of the genome of the present members. Finally, the establishment of a fourth genus within the family Closteroviridae, comprising the unassigned putative species Grapevine leafroll-associated virus 7 (GLRaV-7), Little cherry virus 1 (LChV-1) and Cordyline virus 1 (CoV-1), is justified based on their molecular and biological characteristics that differ from those of members of the other three genera of the family.