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

Department of Entomology, National Taiwan University, Taipei 106, Taiwan.
Phytopathology (Impact Factor: 2.97). 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.

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    ABSTRACT: Grapevine leafroll disease (GLD) is one of the most important grapevine viral diseases affecting grapevines worldwide. The impact on vine health, crop yield, and quality is difficult to assess due to a high number of variables, but significant economic losses are consistently reported over the lifespan of a vineyard if intervention strategies are not implemented. Several viruses from the family Closteroviridae are associated with GLD. However, Grapevine leafroll-associated virus 3 (GLRaV-3), the type species for the genus Ampelovirus, is regarded as the most important causative agent. Here we provide a general overview on various aspects of GLRaV-3, with an emphasis on the latest advances in the characterization of the genome.The full genome of several isolates have recently been sequenced and annotated, revealing the existence of several genetic variants.The classification of these variants, based on their genome sequence, will be discussed and a guideline is presented to facilitate future comparative studies. The characterization of sgRNAs produced during the infection cycle of GLRaV-3 has given some insight into the replication strategy and the putative functionality of the ORFs. The latest nucleotide sequence based molecular diagnostic techniques were shown to be more sensitive than conventional serological assays and although ELISA is not as sensitive it remains valuable for high-throughput screening and complementary to molecular diagnostics.The application of next-generation sequencing is proving to be a valuable tool to study the complexity of viral infection as well as plant pathogen interaction. Next-generation sequencing data can provide information regarding disease complexes, variants of viral species, and abundance of particular viruses. This information can be used to develop more accurate diagnostic assays. Reliable virus screening in support of robust grapevine certification programs remains the cornerstone of GLD management.
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    ABSTRACT: The grape mealybug, Pseudococcus maritimus (Ehrhorn), and European fruit lecanium scale, Parthenolecanium corni (Bouché), are the predominant species of Coccoidea in Washington State vineyards. The grape mealybug has been established as a vector of Grapevine leafroll-associated virus 3 (GLRaV-3) between wine grape (Vitis vinifera L.) cultivars, elevating its pest status. The objective of this study was to determine if GLRaV-3 could be transmitted between Vitis x labruscana L. and V. vinifera by the grape mealybug and scale insects. Three transmission experiments were conducted with regard to direction; from V. vinifera to V. x labruscana L., from V. x labruscana L. to V. x labruscana L., and from V. x labruscana L. to V. vinifera. Each experiment was replicated 15 times for each vector species. Crawlers (first-instars) of each vector species were allowed 1-wk acquisition and inoculation access periods. The identities of viral and vector species were confirmed by reverse transcription-polymerase chain reaction, cloning, and sequencing of species-specific DNA fragments. GLRaV-3 was successfully transmitted by both species in all experiments, although Ps. maritimus was a more efficient vector under our experimental conditions. To the best of our knowledge, this study represents the first documented evidence of interspecific transmission of GLRaV-3 between two disparate Vitis species. It also highlights the potential role of V. x labruscana L. in the epidemiology of grapevine leafroll disease as a symptomless source of GLRaV-3 inoculum.
    Environmental Entomology 12/2013; 42(6):1292-8. · 1.31 Impact Factor

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