Characterisation of Tomato fruit yellow ring virus: a new Tospovirus species infecting tomato in Iran

During surveys for Tomato spotted wilt virus (TSWV) in the major tomato production areas of Iran, tomato fruits showing a bright yellow ring pattern were observed, from which a tospovirus was isolated by mechanical transmission to herbaceous hosts. The virus originated from the Varamin area where >30% of the tomato crop was infected with TSWV. Although typical tospovirus virions were found by electron microscopy, a panel of antibodies used for detection and identification of tospoviruses by ELISA failed to react with this isolate. An antiserum against virus nucleoprotein preparations (DSMZ-AS0526) reacted specifically with plants infected with the new isolate but not with other tospoviruses.

Analysis of the S RNA genome comprising the N protein gene (275 aa; GenBank accession AJ493270) and a segment of the L Gene (GenBank accession AJ493271), to determine the taxonomic position of the virus, confirmed that this is a distinct tospovirus species, sharing 72-75% nucleoprotein aa identity with isolates of Iris yellow spot virus (IYSV), it's closest relative. A 42-45% N protein similarity with N gene sequences of tospoviruses from Asia (Watermelon silver mottle virus, Melon yellow spot virus and Watermelon bud necrosis virus) and only 28-30% aa sequences in common with tospoviruses from Europe-Africa (TSWV, Tomato chlorotic spot virus and Groundnut ringspot virus), further confirmed it's taxonomic position.

The absence of any detectable serological relationships and the limited sequence similarity with IYSV and other tospoviruses, justifies the classification of this new virus as a distinct species of the genus Tospovirus for which we propose the name Tomato fruit yellow ring virus (TFYRV). This virus has an extensive host range (Ghotbi et al., 2005) but it is found most often in tomato and in mixed virus infections with TSWV.