Date: 23 March 2007
From: ProMED-mail <promed@promedmail.org>
From: Richard Hamilton <rihamilto@shaw.ca>
Source: Plant Research International, Wageningen UR (report accessed on Fri 23 Mar 2007) [edited] <click HERE>

Scientists of Plant Research International, part of Wageningen UR [Wageningen University and Research Center in The Netherlands], have identified a dangerous tomato virus. This virus causes ever-increasing damage in Spanish tomato growing as cause of the Torrado ("roasted") disease. The scientists recently published their findings in Archives of Virology.

The identification of the virus will enable plant breeders to develop virus-resistant varieties for tomato growers facing the Torrado disease. The virus appears to be a completely new plant virus that could not be assigned to any existing virus genus. The virus causes necrosis of the leaves and thus may result in considerable yield loss. The plants look as if they are burned, hence the name Torrado.

There are recent reports of the new disease spreading further.

Spanish scientists suspect that the virus is spread by whiteflies.

Some years ago, the Wageningen scientists, in cooperation with the breeding company De Ruiter Seeds, investigated the 1st plant samples from the southeast of Spain. Large numbers of filamentous virus particles were found in the diseased plants. These were particles of the already known Pepino mosaic virus (PepMV). The scientists also found other, spherical, virus particles.

The use of so-called indicator plants, not susceptible to the Pepino mosaic virus but susceptible to the new virus, made it possible to separate the new virus from the PepMV and to propagate it for further research. The virus indeed appeared to be capable to cause the same disease symptoms in tomato plants as those observed in Spain.

The genetic material of this virus consists of two separate RNA segments. Determination of the RNA nucleotide sequence and comparison with data in worldwide databases yielded no viruses with similar sequences. The virus cannot only be considered as a new species; it is so different from known viruses that it can be said to it belongs to a yet unknown genus. In their publication in Archives of Virology the authors propose to name the virus 'tomato torrado virus'.

--

Dick Hamilton
Former Plant Disease Moderator
Canada
<rihamilto@shaw.ca>

[A new virus was isolated from tomato plants from the Murcia region in Spain which showed symptoms of 'torrado disease'; very distinct necrotic, almost burn-like symptoms on leaves of infected plants. The virus particles are isometric with a diameter of approximately 28 nanometers (nm). The viral genome consists of 2 (+)ssRNA (single-stranded RNA) molecules of 7793 (RNA1) and 5389 (non-transcribed spacer) nts (RNA2). RNA1 contains one open reading frame (ORF) encoding a predicted polyprotein of 241 kDa (kiloDalton) that shows conserved regions with motifs typical for a protease-cofactor, a helicase, a protease and an RNA-dependent RNA polymerase. RNA2 contains 2, partially overlapping ORFs potentially encoding proteins of 20 and 134 kDa. These viral RNAs are encapsidated by 3 proteins with estimated sizes of 35, 26 and 23 kDa.

Direct protein sequencing mapped these coat proteins to ORF2 on RNA2.

Phylogenetic analyses of nucleotide and derived amino acid sequences showed that the virus is related to but distinct from viruses belonging to the genera _Sequivirus_, _Sadwavirus_, and _Cheravirus_.

This new virus, for which the name tomato torrado virus is proposed, most likely represents a member of a new plant virus genus. - Former Mod. DH]