Mealybug Transmission of Grapevine Leafroll Viruses: An Analysis of Virus–Vector Specificity

TLDR

Grapevine leafroll disease is caused by a complex of closteroviruses, some of which are transmitted by insect vectors, but the specificities of these virus–vector interactions remain poorly understood, especially as mealybug-mediated spread becomes increasingly important worldwide. The study aimed to identify vector species and assess vector–pathogen specificity in grapevine leafroll virus transmission by conducting biological assays and phylogenetic analyses of several GLRaVs and their mealybug vectors, and it calls for further testing of additional mealybug species. The authors used biological assays and phylogenetic analyses on plants infected with multiple GLRaVs, screening transmission by the mealybug species Planococcus ficus and Pseudococcus longispinus. They found that GLRaV-4 and GLRaV-9 are transmitted by mealybugs, that Planococcus ficus can transmit five GLRaVs, and overall there is no evidence of vector–virus specificity in mealybug transmission of GLRaVs.

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.