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Date: June 11, 2007
Source: Viet Nam News [edited]
<http://vietnamnews.vnagency.com.vn/showarticle.php?num=01COM110607>

Crops still at risk of epidemics

The Vietnam Economic Times newspaper spoke with Nguyen Quang Minh, director of the Plant Protection Department, about eradicating brown hoppers and related plant diseases:

"By June 8 [2007], the brown hopper area was 10 419 ha [25 745 acres], a decrease of 73 ha [180.38 acres] from the previous week.
The infection rate is low at 1000 hoppers per square metre. The areas of rice with yellow stunt disease have lessened since last week to
52.4 ha [129.48 acres], a decrease of 742 ha [1833.5 acres] week-on-week. About 356 ha [879.7 acres] of Dong Thap, Vinh Long, Bac Lieu, Hau Giang, Long An and Tay Ninh provinces reportedly are still battling the diseases.

"The eradication of yellow and stunt rice diseases in the districts of Hong Dan (Bac Lieu Province), Chau Thanh, Long My (Hau Giang) and the province of Tay Ninh is very slow. There isn't enough machinery to take care of the problem; farmers are waiting around for assistance.

"The Plant Protection Department is co-operating with local areas to find a solution. We focus on helping farmers be vigilant over their rice fields and spray insecticide that kills brown hoppers. In provinces like Kien Giang, An Giang and Dong Thap, better brown hopper prevention methods should be put in place so summer-autumn and autumn-winter rice crops aren't affected.

"The growing seasons have been affected by brown hoppers. Officials of the Food and Agriculture Organisation were surprised at our method of minimising the spread of brown hoppers, but it's the most effective way we've found so far. It's necessary to raise water levels to cover the rice seedlings so brown hoppers will emerge and be easily seen, making killing them much easier. Farmers who don't follow the schedule we've set for crop seasons will get more brown hoppers.

"The Ministry of Agriculture and Rural Development asked the Mekong Delta Rice Institute and Plant Protection Institute to test any chemical products against these rice diseases. But as far as we know, there hasn't been any treatment for the viruses. A kind of fertiliser was used for some fields in Long An which helps brings yellow leaves back to life but can't kill the virus."

--
Communicated by:
J. Allan Dodds
Former ProMED-mail plant disease moderator <dodds@ucr.edu>

[In addition to _Rice grassy stunt virus_ (RGSV) and _Rice ragged stunt virus_ (RRSV) discussed in the previous post no. 20070611.1899 ('Virus disease, rice - Viet Nam'), at least one further rice virus is implicated in this report: _Rice yellow stunt virus_ (RYSV; genus _Nucleorhabdovirus_, family _Rhabdoviridae_; synonym _Rice transitory yellowing virus_, RTYV). Its only natural host is rice where it causes leaf yellowing, reduced tillering, and mild stunting. Later, infected plants develop normal-looking leaves and may appear healthy, but symptoms may reappear after this temporary recovery. RYSV is transmitted in a persistent manner by the green rice leafhoppers _Nephotettix cincticeps_, _N. nigropictus_ and _N. virescens_. Since RGSV and RRSV are transmitted by brown planthoppers (_Nilaparvata lugens_) it appears that there may be a mixture of different brown and green hopper species in the region.

The incidence of RYSV is generally low in the 1st rice crop and high in the 2nd crop. After the harvest of late-planted rice, RTYV overwinters in rice stubble or in the vector.

Weed hosts may also play a role in the infection cycle. RYSV shares common vectors (_N. cincticeps_ and _N. nigropictus_) with _Rice dwarf virus_ (RDV; genus _Phytoreovirus_, family _Reoviridae_) and they frequently occur together. Whether this is the case in southern Viet Nam is unclear from the report above.

Green rice leafhoppers (_N. virescens_ and other spp.) are also vectors of _Rice tungro bacilliform virus_ (RTBV; genus "_RTBV-like viruses_", family _Caulimoviridae_) and _Rice tungro spherical virus_ (RTSV; genus _Waikavirus_, family _Sequiviridae_). Both these viruses together cause the rice tungro disease and are also present in parts of the Mekong Delta area (see link for distribution map below).
Tungro is one of the most damaging rice diseases in South East Asia with losses up to 100 percent.

Maps:
Map of Viet Nam and neighbours:
<http://www.lib.utexas.edu/maps/middle_east_and_asia/vietnam_pol01.jpg>
Distribution map of several rice viruses in southern Viet Nam:
<http://www.kper.or.kr/img/board/75ho_info_05.jpg>

Pictures
_Nucleorhabdovirus_ particles, electron micrograph:
<http://www.rothamsted.bbsrc.ac.uk/ppi/links/pplinks/virusems/b7.jpeg>
_Rice dwarf virus_ particles, electron micrograph:
<http://www.apsnet.org/education/IntroPlantPath/PathogenGroups/plantViruses/images/fig03.jpg> 

_N. virescens_:
<http://www.deptan.go.id/ditlin-tp/PHOTO%20DAN%20PETA/PHOTO/OPT/Padi/Copy%20of%20WDH1.jpg> 
_Nephotettix cincticeps_:
<http://www.ne.jp/asahi/rhyncha/index/image7/0616.jpg>
_N. nigropictus_:
<http://www.ento.csiro.au/aicn/images/cain3872.jpg>
Tungro symptoms on rice plant:
<http://www.irri.org/media/achievements/images/Tungro.jpg>

Links:
_Rice yellow stunt virus_ description:
<http://www.ncbi.nlm.nih.gov/ICTVdb/ICTVdB/01.062.0.05.008.htm>
_Rice dwarf virus_ description: 
<http://image.fs.uidaho.edu/vide/descr686.htm>
_Rice tungro bacilliform virus_ description:
<http://image.fs.uidaho.edu/vide/descr695.htm>
_Rice tungro spherical virus_ description:
<http://image.fs.uidaho.edu/vide/descr696.htm>
Rice tunrgo fact sheet:
<http://www.knowledgebank.irri.org/ricedoctor_mx/Fact_Sheets/Diseases/Tungro.htm>
H. Hibino (1996). Biology and epidemiology of rice viruses. Annu.
Rev. Phytopathol. 34, 249-74:
<http://arjournals.annualreviews.org/loi/phyto>
Green leafhopper information:
<http://www.knowledgebank.irri.org/RiceDoctor_MX/Fact_Sheets/Pests/Green_Leafhopper.htm>
Brown planthopper information:
<http://www.knowledgebank.irri.org/RiceDoctor_MX/Fact_Sheets/Pests/Planthopper.htm#Common>
Brown planthopper biotypes:
<http://www.springerlink.com/index/V2N89L31T2573778.pdf>
- Mod.DHA]

[see also in the archive:
Virus disease, rice - Viet Nam 20070611.1899
2006
----
Ragged and grassy stunt, brown planthopper, rice - Viet Nam 20061103.3157]

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