May 9, 2005
Source:  British Society for Plant Pathology, New Disease Reports, Vol 11 [edited]
<http://www.bspp.org.uk/ndr/july2005/2005-34.asp>

Characterisation of tomato fruit yellow ring virus: a new Tospovirus species infecting tomato in Iran
S Winter, M Koerbler, DSMZ Plant Virus Division, c/o BBA, Braunschweig, Germany; N Shahraeen, Plant Pests and Diseases Research Institute, Ministry of Agriculture, Tehran, Iran; D-E Lesemann, Institute of Plant Virology, Microbiology and Biosafety, BBA, Braunschweig, Germany. Accepted for publication 19 Apr 2005.

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 over 30 per cent 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 to 75 per cent nucleoprotein aa identity with isolates of Iris yellow spot virus (IYSV), its closest relative.

A 42 to 45 per cent 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 to 30 per cent aa sequences in common with tospoviruses from Europe-Africa (TSWV, Tomato chlorotic spot virus and Groundnut ringspot virus), further confirmed its 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.

Reference:
Ghotbi T, Shahraeen N, Winter S. Occurrence of Tospoviruses in ornamental and weed species in Markazi and Tehran Provinces in Iran. Plant Disease 2005; 89: 425-9.

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[This piece is a good example of virus evolution. The genus _Tospovirus_ (family _Bunyaviridae_) is one of 5 genera in the family, and the only one that infects plants. Tospoviruses, transmitted by thrips, are capable of
infecting a large range of important crops. The type member, Tomato spotted wilt virus (TSWV), has one of the broadest host ranges among plant viruses. It is well established in many parts of the world and affects crops such as potato, lettuce, tomato, pepper, groundnut, mungbean, and tobacco. Rough estimates calculate the worldwide loss due to tospoviruses at USD 1 billion.

Lettuce crops in Hawaii have suffered serious damage due to TSWV for several successive years, forcing growers to switch to other crops. Annual losses due to peanut bud necrosis virus (PBNV) in Asia are estimated at more than US$ 89 million. There are at least 15 recognized tospoviruses.

A new approach to disease management of TSWV is peptide-mediated, broad spectrum plant resistance, as described by Rudolf, Schreir, and Uhrig at the Max Planck Institute for Plant Breeding Research, Cologne and Bayer Crop Science in Mohnheim, Germany (<http://www.pnas.org/cgi/content/full/100/8/4429>, to which the numbered references in this comment refer, and which includes a comprehensive review). An example is the development of broad spectrum resistance which is expressed by specific viral proteins. There are unambiguous examples of protein-mediated virus resistance -- mainly expression of viral coat proteins (3,4,10) -- but cases of protein-dependent pathogen-derived resistance due to expression of viral movement proteins or replicases are
also known (9,11,12). In some instances, resistance is based on the expression of intact, functional proteins; in others the expression of the intact protein leads only to weak resistance or even to enhanced susceptibility. In contrast, expression of a dysfunctional protein may lead to strong resistance (12,13). Presence of the viral gene product in inappropriate amounts, form or time, is thought to interfere with viral infection. However, in some cases it is difficult to distinguish between an RNA- and protein-mediated resistance (8,9). Despite the number of
successful examples, the molecular basis of protein-mediated virus resistance is, in most cases, not understood. Further research and development are required.

Links: <http://www.mcb.uct.ac.za/tutorial/emerging%20plant%20viruses.htm>
<http://www.biotech-monitor.nl/3207.htm#box>
- Mod.DH]