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First report of Tobacco streak virus on faba bean in Sudan

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A ProMED-mail post
ProMED-mail is a program of the International Society for Infectious Diseases

A ProMED-mail post
<http://www.promedmail.org>
ProMED-mail is a program of the
International Society for Infectious Diseases <http://www.isid.org>

Date: April 8, 2008
Source: British Society for Plant Pathology, New Disease Reports (NDR) vol. 17 [edited]
<http://www.bspp.org.uk/ndr/july2008/2008-22.asp>

[Ref: MA Ali, et al: _Tobacco streak virus_ infecting faba bean (_Vicia faba_) reported for the 1st time. BSPP New Disease Reports 2008; 17]

During the period December 2005 to January 2006, unusual leaf symptoms suggestive of a virus infection were observed in faba bean (_Vicia faba_) in fields in the Gezira area and Northern parts of Sudan. Symptoms in beans were coincident with a high level of crop infestation by _Aphis craccivora_ that might play a role in the transmission of the virus. Chlorotic mottling and/or mosaic symptoms were accompanied by black streaks on stems and leaf petioles. In some bean varieties, severe leaf chlorosis (Fig. 1) subsequently developed into browning and blackening of the entire leaves (Fig. 2), resulting in plant death (Fig. 3).

Extracts from bean leaves were mechanically inoculated onto a range of host plants, and _Nicotiana benthamiana_ and _Chenopodium quinoa_ were identified as suitable propagation hosts. Electron microscope analysis of leaf extracts from infected _C. quinoa_ revealed virus-like particles with isometric particles approximately 30 nanometers in diameter.

A specific antiserum against the purified virus was produced, and the size of the putative coat protein was estimated to be between 29 and 30 kDa. Using several reference viruses for a serological comparison, the virus isolated from faba bean was found to be related to _Tobacco streak virus_ (TSV), a virus that is a serious pathogen of groundnut, sunflower, and okra in India.

The identity of the faba bean virus isolate was confirmed by reverse transcription-polymerase chain reaction (RT-PCR) and sequence analysis. A comparison of the deduced 237 amino acid coat protein sequence revealed between 90 and 92 percent sequence identity with the coat proteins of TSV isolates from sunflower, cotton, and a
number of other crops in India. The closest relationship (98 percent identity) of TSV from the Sudan was found with a TSV isolate from the ornamental _Impatiens neuguinea_. An analysis of TSV isolates from legumes including _V. faba_ revealed a 92 percent amino acid sequence identity with a soybean isolate from India, and only a distant relationship to a TSV soybean isolate from Brazil (83 percent). This shows a distinct geographic distribution of the TSV isolates from faba bean in Sudan.

To our knowledge this is the 1st report of the natural occurrence of TSV in _V. faba_.

Figures
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1. severe leave chlorosis caused by TSV on faba bean
<http://www.bspp.org.uk/ndr/july2008/2008-22-1.jpg>
2. browning and blackening of faba bean leaves caused by TSV
<http://www.bspp.org.uk/ndr/july2008/2008-22-2.jpg>
3. death of faba bean plant due to TSV infection
<http://www.bspp.org.uk/ndr/july2008/2008-22-3.jpg>

--
Communicated by:
ProMED-mail
<promed@promedmail.org>

[_Tobacco streak virus_ (genus _Ilarvirus_] affects a number of crops, including bean, sunflower, peanut, maize, soybean, and a range of vegetable and ornamental species. It is probably distributed worldwide and has been reported to be spreading in North America and Oceania. It is transmitted by thrips vectors (_Frankliniella
occidentalis_ and _Thrips_ spp.), possibly by allowing virus from the surface of infected pollen to enter through feeding wounds. Weed species, for example _Parthenium_ species, may serve as pathogen reservoirs and potential sources of infected pollen (see previous ProMED-mail post no. 20070419.1289). TSV can also be transmitted by mechanical inoculation and grafting, by pollen to the pollinated plant, and it is seed-transmitted in some species to different extents. It is not transmitted by contact between plants.

While this is the 1st report of a natural field infection of faba beans with TSV, _V. faba_ has been reported previously as an experimental host susceptible to mechanical inoculation. Furthermore, aphids do not cause major feeding wounds like thrips and are not known to transmit TSV, and therefore the _A. craccivora_ reported
above to have been present in the same crop are not likely to have been involved as vectors. It appears that further work is needed to elucidate the epidemiology of TSV in field crops of faba beans.

Maps
Sudan:
<http://www.mapsofworld.com/sudan/maps/sudan-map-political.jpg> and
<http://healthmap.org/promed?v=13.8,30,5>
Location of El Gezira administrative region:
<http://www.sudan.net/government/admnmap.html>

Pictures
TSV symptoms on sunflower:
<http://www.dpi.qld.gov.au/images/PlantIndustries_HealthPestsDiseaseAndWeeds/Sunflower-TSV-SeedlingDeath-168_rdax_168x134.jpg
and
<http://www.dpi.qld.gov.au/images/PlantIndustries_HealthPestsDiseaseAndWeeds/Sunflower-TSV-RottenPith-168_rdax_168x134.jpg>
TSV on raspberries:
<http://www.canr.msu.edu/vanburen/rbfig3.jpg>

Links
TSV infection of sunflower:
<http://www.dpi.qld.gov.au/cps/rde/xbcr/dpi/CQSFS-Sunflower-TobaccoStreakVirus.pdf>
TSV on soybean:
<http://www.planthealth.info/viruses_symptoms.htm>
TSV taxonomy and description:
<http://www.ncbi.nlm.nih.gov/ICTVdb/ICTVdB/00.010.0.02.017.htm>. - Mod.DHA]

[see also in the archive:
2007
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TSV, mungbean - Australia (QLD): 1st report 20070419.1289
2006
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Tobacco streak virus, sunflower - Australia: 1st report 20060731.2118
2005
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Tobacco streak virus, mung bean - India: 1st report 20051214.3595
2003
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Tobacco streak virus, cucumber - India: 1st report 20030918.2363
2002
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Soybean viruses, first reports - Iran 20020513.4189
2001
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Tobacco streak disease, peanut - India 20011118.2839
Tobacco streak virus, sunflower - India 20010830.2057]



 

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