A ProMED-mail post
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International Society for Infectious Diseases <http://www.isid.org>
Date: Mon 29 Mar 2010
Source: Viet Nam News (VNS) [edited]
Farmers should not underestimate the black streaked dwarf rice disease, which has been causing widespread panic because of its complicated development and unexpected consequences, according to agricultural officials.
The warning was made after farmers at some northern locales reported that infected crops had shown signs of recovery. Tran Xuan Dinh, Thai Binh Department of Agriculture and Rural Development, said that the rice may look healthy on the outside, but the disease may still be affecting its quality, and farmers could see poor harvests and heavy losses. He said that the disease had affected paddy fields in the province last year  and had ruined more than 3000 ha [approx 7400 acres] of rice.
Ngo Tien Dung, Plant Protection Department, said that there was currently no way of stamping out the disease. A report showed that currently 23 of the 41 provinces and cities have their rice fields infected, covering a total area of over 20 360 ha [approx 50 000 acres]. About 10 percent of these fields were completely ruined. Thai Binh was the worst-hit province, with nearly 18 000 ha [approx 44 000 acres] of infected rice. The disease was reported to have rapidly spread across northern Lai Chau, Ninh Binh, and Bac Giang and in central Thua Thien-Hue. In Ninh Binh, for example, more than 200 ha [approx 500 acres] of rice were found to be infected with the disease each day. Initial tests showed that rice fields in 5 disease-free districts in the province were also showing signs of stunting. Thus, more than 700 ha [approx 1700 acres] of infected rice were pulled up.
Bui Si Doanh, Plant Protection Department, said the State would supply agrochemicals, financial support, and rice for each person for the next 6 months. Vice minister Bui Ba Bong said that the disease was predicted to be more complicated than last year . Thus, farmers should keep an eye on their fields and promptly report any problems to local authorities.
[Black streaked dwarf disease (BSDD) of rice due to _Rice black streaked dwarf virus_ (RBSDV; genus _Fijivirus_) is known to cause serious crop losses in South-East Asia. Symptoms include darkening and distortion of leaves, black streaked tumours along leaf veins, and severe stunting of plants. It also affects some other graminaceous hosts including maize, wheat, oat and barley and is spread by planthoppers including _Laodelphax striatellus_ and _Unkanodes_ species.
In 2009, the spread of a new virus associated with BSDD symptoms, but transmitted by the white backed planthopper (WBPH, _Sogatella furcifera_), which is not a vector of RBSDV, was reported from southern China and northern Viet Nam. The new virus has been tentatively named Southern rice black streaked dwarf virus (SRBSDV).
RBSDV and the closely related _Maize rough dwarf virus_ (MRDV) have both been classed into the serogroup 2 of _Fijivirus_, and SRBSDV appears to belong to the same group. Disease management for rice viruses includes cultural practices, vector control, and use of cultivars with reduced sensitivity or resistance to the virus, the vector, or both.
Besides BSDD, other rice virus diseases are also being reported from Viet Nam (see ProMED-mail posts listed below). While the new SRBSDV and an increase in WBPH numbers in the region are doubtless a major concern, it is not certain that the disease statistics in the item above are confirmed to be only due to SRBSDV, or whether they may represent the combined effect of several of the rice viruses.
Viet Nam and neighbours:
Viet Nam provinces:
Black streaked dwarf symptoms on rice leaf:
Symptoms of SRBSDV:
White backed planthopper:
_Fijivirus_ particles, electron micrograph:
Additional news story:
Description and preliminary taxonomy of SRBSDV:
RBSDV taxonomy and description:
Genus _Fijivirus_ taxonomy:
Information on rice planthoppers, including white backed:
Review of rice viruses (including RBSDV), biology and epidemiology:
Multiple disease, rice - Viet Nam (02) 20100322.0906
Multiple disease, rice - Viet Nam 20100307.0749
Undiagnosed diseases, rice - Viet Nam: (northern) 20100114.0162
Black streaked dwarf, rice - China, Viet Nam: new virus 20091217.4263
Ragged stunt, rice - Viet Nam 20090803.2722
Rice viruses - Viet Nam: alert 20090608.2118
Rice diseases - Viet Nam 20081017.3291
Virus diseases, rice - Viet Nam: update (02) 20080322.1093
Virus & blast diseases, rice - Viet Nam (Mekong Delta) 20080204.0454
Virus diseases, rice - Viet Nam: update 20080118.0221
Rice grassy stunt virus - Viet Nam (Mekong Delta) 20070725.2382
Virus disease, rice - Viet Nam (02) 20070614.1939
Virus disease, rice - Viet Nam 20070611.1899
Ragged and grassy stunt, brown planthopper, rice - Viet Nam 20061103.3157
Maize rough dwarf virus, maize - Greece: 1st report 20031115.2840]