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Date: November 2007
Source: The American Phytopathological Society, Plant Disease 2007; 91(11): 1513 [edited]
<http://apsjournals.apsnet.org/doi/abs/10.1094/PDIS-91-11-1513B>

[Reference: JA Mauricio-Castillo et al: 1st report of _Tomato golden mottle virus_ on _Lycopersicon esculentum_ and _Solanum rostratum_ in Mexico. Plant Dis 2007; 91(11): 1513; DOI: 10.1094/PDIS-91-11-1513B]

The Rioverde Valley is an important farming area of the San Luis Potosi State in the north-central region of Mexico, where a variety of horticultural crops (that is, tomato, pepper, cucumber, and watermelon) are annually cultivated. In the summer of 2005, a number of plants exhibiting a variety of symptoms, including leaf yellowing,
curling, and stunted growth, were observed in several tomato (_Lycopersicon esculentum_ L.) fields. The presence of whiteflies (_Bemisia tabaci_ Genn.) and the symptoms seemed to suggest a begomoviral etiology.

Leaves of 12 symptomatic tomato plants and 7 plants of the weed _Solanum rostratum_ growing in the same area were collected from several fields throughout the Rioverde area and assessed for the presence of begomoviruses (genus _Begomovirus_, family _Geminiviridae_) by PCR [polymerase chain reaction]. Amplicons [DNA products] of 1.4 kb [kilobasepairs] were derived from viral DNA-A present in all examined _S. rostratum_ and tomato samples and were analyzed by restriction fragment length polymorphism (RFLP). Several restriction fragment patterns were observed, indicating the occurrence of different begomoviruses in the sampled fields.

Sequencing of amplicons derived from one _S. rostratum_ plant revealed the concurrent presence of _Tomato severe leaf curl virus_ (ToSLCV) and a distinct virus displaying a high sequence identity with _Tomato golden mottle virus_ from Guatemala (ToGMoV). Restriction fragment patterns identical to that of the ToGMoV-like isolate were found in 3 additional _S. rostratum_ plants and 5 tomato samples. PCR products encompassing the complete DNA-A component of ToGMoV were obtained from one tomato sample. The 2614-bp DNA-A sequence of the Rioverde isolate displayed 93 percent sequence identity with the Guatemalan isolate of ToGMoV.

In addition, a number of _B. tabaci_ specimens of unidentified biotype were collected in one tomato field. PCR analysis of viral DNA present in the whiteflies was carried out. One of the begomoviral DNA-A genomes isolated from the whiteflies displayed 99 percent sequence identity with the virus isolated from plants.

Previously, ToGMoV had been found only in Central America, but this report considerably expands its known geographical distribution.

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[Begomoviruses affect many economically important crops causing symptoms often including leaf yellowing, distortion, stunting, reduced plant vigour, and yield losses. Tomato is a host of a number of these viruses, including for example species in the tomato leaf curl and tomato yellow leaf curl viral clades. Begomoviruses are
transmitted by whitefly vectors and can often also be transmitted by mechanical means and grafting. Whiteflies are widely distributed and have a very wide host range of more than 600 plant species. Weed species can serve as insect reservoirs making control difficult. Whiteflies have been reported to transmit over 100 virus species, including many begomoviruses, but also cause serious crop damage by direct feeding.

Disease management of begomoviruses relies on control of the vector and possible pathogen and/or vector reservoir plants. This has occasionally caused problems with chemical residues on fruits. In some cases, crop cultivars with increased virus resistance are available.

Both ToGMoV and ToSLCV have a bipartite genome (called DNA-A and DNA-B in the report above). While ToSLCV strains have been reported from Mexico, Guatemala, Honduras, Nicaragua, and Cuba from both tomato and cucumber, only one strain of ToGMoV from tomato from Guatemala had been reported previously. In the item above, a 2nd strain of ToGMoV is being reported as well as a 2nd natural host and a new location for this virus. Furthermore, the finding of ToGMoV sequences in _B. tabaci_ demonstrates that it is a vector of the new strain. _B. tabaci_ is believed to be a species complex with a number of recognised biotypes varying in their distribution and vector activities.

Maps
Mexico:
<http://www.mexico.us/map.htm> and
<http://healthmap.org/promed?v=24,-102.5,5>
San Luis Potosi:
<http://travelamap.com/mexico/sanluispotosi_I.htm>

Pictures
Yellowing and leaf curl begomovirus symptoms on tomato:
<http://www2.dpi.qld.gov.au/images/13644.jpg>
Electron micrograph of _Begomovirus_ particles:
<http://www.ncbi.nlm.nih.gov/ICTVdb/WIntkey/Images/em_gemin_2.jpg>
_B. tabaci_ picture gallery:
<http://www.eppo.org/QUARANTINE/insects/Bemisia_tabaci/BEMITA_images.htm>
_S. rostratum_ (buffalo burr):
<http://fireflyforest.net/images/firefly/2006/July/Solanum-rostratum-1.jpg>

Links
ToGMoV strains, distribution, taxonomy:
<http://gemini.biosci.arizona.edu/viruses/togmov/index.htm> and
<http://www.catalogueoflife.org/annual-checklist/show_species_details.php?record_id=1442570>
ToSLCV strains, distribution, taxonomy:
<http://gemini.biosci.arizona.edu/viruses/toslcv/index.htm> and
<http://www.catalogueoflife.org/annual-checklist/show_species_details.php?record_id=1442619>
Genus _Begomovirus_ taxonomy:
<http://www.ncbi.nlm.nih.gov/ICTVdb/ICTVdB/00.029.0.03.htm>
_Begomovirus_ species list via
<http://www.ncbi.nlm.nih.gov/ICTVdb/Ictv/index.htm>
List of viruses in tomato yellow leaf curl and leaf curl complexes:
<http://www.ncbi.nlm.nih.gov/ICTVdb/Ictv/vn_indxT.htm>
_B. tabaci_ taxonomy and biotypes:
<http://www.issg.org/database/species/ecology.asp?fr=1&si=106>
Scientific name of tomato:
<http://www.plantnames.unimelb.edu.au/Sorting/Lycopersicon.html>.  - Mod.DHA]