Strawberry Necrotic Shock Virus: A New Virus Previously Thought to Be Tobacco Streak Virus

Tobacco streak virus (TSV) has a wide host range that exceeds 80 species (Fulton, 1948). Most of the efforts carried out previously comparing TSV isolates was based on immunological relations between them. The isolates of the virus from Fragaria and Rubus have been considered to be very closely related if not identical while they are distinct from isolates of other hosts. While trying to characterize the viruses associated with pallidosis disease, we cloned part of the genome of a virus with homology to TSV but distinct enough to be considered a unique virus and not an isolate of TSV. Here we report the complete sequence of RNA 3 of the virus from a strawberry isolate as well as the sequence of the coat protein gene from an additional nine strawberry as well as five Rubus isolates. The data suggest that Fragaria and Rubus are infected with a virus closely related to TSV, designated as Strawberry necrotic shock virus from the name given by Frasier et al. in the first report of the virus infecting strawberry. We were unable to acquire any amplicons utitizing reverse transcription-polymerase chain reaction with primers derived from the published sequence for TSV, an indication that strawberry and Rubus may not be hosts for TSV. INTRODUCTION Tobacco streak virus (TSV) is one of the more than 30 virus and virus-like agents infecting strawberry (Spiegel and Martin 1998). TSV is the type member of the Ilarvirus group of the family Bromoviridae. Viruses belonging to the family have tripartite genomes that are encapsidated in quasi-isometric particles of 27-35 nm. RNA 1 encodes the viral replicase that has methyltransferase and helicase motifs and in the case of Brome mosaic virus is involved in the anchoring of the replication complex in the membranes (den Boon et al., 2001). RNA 2 encodes the viral polymerase and some members of the family also encode a protein that may function as a suppressor of RNA interference (gene silencing) (Xin et al., 1998). RNA 3 encodes the movement and coat protein of the virus. The coat protein is expressed from a subgenomic RNA (RNA 4) and is needed for long distance movement and genome activation (Jaspars, 1999). Ilarviruses are pollen and seed transmitted and thrips transmission has been demonstrated for several members of the genus (Sdoodee and Teakle 1987). TSV in small fruits was documented first in the 1960’s (Frazier et al., 1962) when it was thought to be a new virus species and given the name Strawberry necrotic shock virus (SNSV). Black raspberry latent virus (BRLV) also was originally thought to be a distinct virus (Converse and Lister 1969). Previous studies with TSV in small fruits were based on symptomatology on indicator plants, serological relationships and/or hybridization studies. Several of the previous studies demonstrated differences between small fruit strains and other strains of TSV. Small fruit strains of TSV were not able to cross-protect plants when challenged with other strains (Fulton, 1978). Stenger et al. (1987) performed Northern blot analysis and where unable to detect the Rubus and strawberry isolates of the virus when using probes developed from the white clover (WC) strain of the virus and vice versa. Proc. X IS on Small Fruit Virus Diseases