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