December 13, 2005
From: ProMED-mail<promed@promedmail.org>
Source: British Society for Plant Pathology, New Disease Reports, Vol. 12 [edited] <http://www.bspp.org.uk/ndr/jan2006/2005-74.asp>

First report of the natural occurrence of tobacco streak virus on blackgram (Vigna mungo)
D Ladhalakshmi, M Ramiah, T Ganapathy, Salah Eddin Khabbaz, Merin Babu, Department of Plant Pathology, Tamil Nadu Agricultural University, Coimbatore, India; M Krishna Reddy, A
Kamalakannan, Indian Institute of Horticultural Research, Hassargutta, Bangalore, India. Accepted for publication 2 Sep 2005.

Blackgram (_Vigna mungo_; family _Fabaceae_) is an important pulse crop in India, Nepal, Bangladesh, and Myanmar. During kharif season of the south west land wind during the monsoon (Jun-Sep 2002), a new disease was observed in the majority of the blackgram growing areas of India.

Symptoms of the disease consisted of brown necrotic lesions on young leaves, with brown streaks on petioles and stems. In severe cases, infected plants were dead. Mechanical inoculation of plant sap from infected plants onto various plant species: _Vigna unguiculata_ cv. 152 (_Fabaceae_), _Nicotiana tabaccum_ (_Solanaceae_), _Chenopodium amaranticolor_ (_Chenopodiaceae_), and _Gomphrena globosa_ (_Amaranthaceae_) produced
necrotic lesions on leaves and streaks on stems. Alternate hosts may also play role in disease epidemiology, since tobacco streak virus (TSV) infects many widely distributed weeds. For example, _Parthenium hysterophorus_
probably plays a major role in the spread of TSV in peanut (_Arachis hypogaea_) (Prasada Rao, et al. 2003).

Infected leaf samples of blackgram tested positive for TSV by DAC-ELISA (Bhat, et al. 2001) using a specific polyclonal antibody (a gift from G Cook, Plant Protection Research Institute, South Africa). Electron microscopic observations of negatively-stained preparations of purified virus from infected blackgram leaves revealed spheres with a diameter of 27 nm; consistent with TSV infection. RT-PCR tests of tissue from diseased blackgram plants using primers specific for the coat protein gene of TSV (Bhat, et al. 2002) resulted in an amplicon of the expected size: ca. 700bp).

SV infects a wide range of hosts in India (Prasada Rao, et al. 2003). This is the 1st report of the natural occurrence of TSV on _Vigna mungo_.

References:
Bhat AI, Anil Kumar, Jain RK, Chander Rao S, Ramiah M. Development of  serological based assays for the diagnosis of sunflower necrosis disease. Annals of Plant Protection Science 2001; 9: 292-6.
Bhat AI, Jain RK, Ramiah M. Detection of tobacco streak virus from sunflower and other crops by reverse transcription polymerase chain reaction. Indian Phytopathology 2002; 55: 216-8.
Prasada Rao RDVJ, Reddy AS, Reddy SV, Thirumala Devi K, Chander Rao S, Manoj Kumar V, et al. The host range of tobacco streak virus in India and transmission by thrips. Annals of Applied Biology 2003; 142: 365-8.

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[TSV is transmitted by _Frankliniella occidentalis_ and _Thrips tabaci_; _Thysanoptera_ (possibly by allowing virus from the surface of infected pollen to enter through feeding wounds; Sdoodee and Teakle, 1987). The virus is transmitted by mechanical inoculation and grafting. TSV is readily transmitted via seed to high levels in _Phaseolus vulgaris_. It is also transmitted by pollen to pollinated plants. Disease management depends mainly on planting virus-free seed.

Links:
<http://www.ingentaconnect.com/content/aab/annals/2003/00000142/00000003/art00014> 
<http://www.apsnet.org/pd/searchnotes/2003/0804-03N.asp>
<http://www.plantpath.wisc.edu/soyhealth/virusepid.htm>
- Mod.DH]

[see also in the archive:
2003
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Tobacco streak virus, cucumber - India: first report 20030918.2363
2001
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Tobacco streak disease, peanut - India 20011118.2839
Tobacco streak virus, sunflower - India 20010830.2057]