Closteroviridae

Abstract

Closteroviridae is a family of plant viruses with filamentous, helically constructed particles showing distinct cross‐banding and varying in length from 650 nm (species with fragmented genome) to over 2000 nm (species with monopartite genome). The genome is a single‐stranded, positive‐sense RNA ( ribonucleic acid ), with size varying from 13 000 to nearly 19 000 nucleotides, thus being among the largest known for plant viruses. The family comprises three genera, Closterovirus , Ampelovirus and Crinivirus , which differ in genome type (monopartite, bipartite or tripartite) and size, and in epidemiological behaviour. Closteroviruses are transmitted by aphids; ampeloviruses by pseudococcid mealybugs and soft scale insects and criniviruses by whiteflies. These viruses are mostly phloem‐restricted, are all transmitted with a semipersistent modality regardless of the type of vector and are pathogenic to a wide range of herbaceous and woody crops, to which they may cause extensive damage. Control is based on preventive measures such as sanitary selection, sanitation and induction of resistance, primarily through conventional breeding. Key concepts: Closteroviridae is a growing family of plant viruses with three genera. All members of the family have filamentous virions with open particle structures and distinct cross‐banding. Closteroviral genomes are among the largest for plant viruses and are highly diversified also within each genus. The family represents a monophyletic lineage that has evolved in a modular way. A characterizing trait of the genera is the type of vectors that mediate transmission from host to host. Virus particles are primarily restricted to the phloem from where they are acquired by the vectors. Virus dissemination over long distances is mediated by infected propagative material, rather than vectors. Most members of the family have a restricted natural host range. Many cause serious, if not devastating, epidemics to herbaceous and woody crops. Disease control relies on preventive measures aimed at reducing vector populations and sources of inoculum. Sanitary selection and sanitation are efficient means for producing certified stocks.

Pest categorisation of Little cherry pathogen (non‐EU isolates)

“…The graft transmissible agent responsible (‘Little cherry pathogen’) was previously considered to be a single virus species but studies have shown that two viruses belonging to the Closteroviridae family, Little cherry virus 1 (LChV1, Jelkmann, ) and Little cherry virus 2 (LChV2, Eastwell and Bernardy, ; Rott and Jelkmann, , ) are associated with the disease. LChV1 is a member of the Velarivirus genus, while LChV2 belongs to the Ampelovirus genus (Martelli et al., ,b; Martelli and Candresse, ). For the sake of simplicity, when collectively referred to, LChV1 and LChV2 will be designated in what follows as Little cherry viruses or LChV.…”

A divergent variant of Grapevine leafroll-associated virus 3is present in California

“…GLRD is caused by several related positive single-stranded RNA virus species in the family Closteroviridae , which contains the largest known plant RNA virus genomes [4]. All GLRD-causing viruses are phloem-limited [5] and infect Vitis hosts [6]. The mealybug-transmitted viruses are in the genus Ampelovirus , and Grapevine leafroll-associated virus 2 , which has no known vector, is in the genus Closterovirus [6].…”