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: 13 Oct 2008
Source: Viet Nam News (VNS) [edited]
<http://vietnamnews.vnagency.com.vn/showarticle.php?num=01DOM131008>

Pests threaten rice fields across the country

More than 10 600 ha (26 193 acres) of rice in the Cuu Long (Mekong) Delta have been affected by ragged stunt rice disease and yellow stunt rice disease, according to the Ministry of Agriculture and Rural Development.

The diseases have also spread to 6200 ha (15 321 acres) of rice in the southeastern provinces of Tay Ninh and Binh Duong. Southern provinces have destroyed more than 600 ha (1483 acres) of infected rice.

Northern provinces in the Hong (Red) Delta, including Bac Giang, Bac Ninh, and Nam Dinh, have 13 600 ha (33 606 acres) of rice affected by rice leaf blight. The northern provinces plant protection departments have told farmers to spray chemicals on affected rice fields.

--
Communicated by:
PRO/MBDS
<promed-mbds@promedmail.org>

[_Rice ragged stunt virus_ (RRSV; genus _Oryzavirus_) is know from a number of countries in Asia. Symptoms include ragged appearance of plants, twisted leaves, vein swelling, and severe stunting. Its only way of spread is vector transmission by brown planthoppers (_Nilaparvata lugens_). Besides rice (_Oryza sativa_), the related
species _O. latifolia_ and _O. nivara_ can also be affected.

_N. lugens_ is one of the worst pests of rice in the Australasian and Pacific Island region. In addition to being a virus vector, it causes yellowing, browning, and drying of plants ('hopper burn') and leaves small injuries exposing the plant to fungal and bacterial infections (for example leaf blight as reported here). _Rice grassy stunt virus_
(RGSV; genus _Tenuivirus_) is transmitted by the same vector and therefore it often occurs together with RRSV. However, RGSV has not been mentioned in the report above.

Rice yellow stunt virus_ (RYSV; genus _Nucleorhabdovirus_; synonym _Rice transitory yellowing virus_) affects only rice causing leaf yellowing, reduced tillering, and mild stunting. Plants may recover temporarily and appear healthy, but symptoms may reappear. RYSV is transmitted by green rice leafhoppers (_Nephotettix_ species). The
incidence of RYSV is generally low in the 1st crop and high in the 2nd. After the harvest of late-planted rice, RTYV overwinters in rice stubble or in the vector.

In tropical regions, levels of rice virus infection and vector density may be very high. Crop losses of up to 100 percent due to some virus diseases have been reported. 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.

Bacterial leaf blight (BLB) of rice is caused by _Xanthomonas oryzae_ pv. _oryzae_. The pathogen causes yellowing and drying of leaves and wilting of seedlings. Yield losses of up to 60 percent have been reported in Asia. The bacterium is short-lived in soil and suspected to be seed-borne, and it is spread mainly by windblown rain and mechanical means. Disease management includes phytosanitation, cultural measures, and use of resistant crop varieties. For more information on BLB, please see previous ProMED-mail posts and links below.

Maps
Map of Viet Nam and neighbours:
<http://www.lib.utexas.edu/maps/middle_east_and_asia/vietnam_pol01.jpg>
<http://healthmap.org/promed?v=14.9,108.5,5>
Viet Nam provinces:
<http://www.angelfire.com/co/hongnam/vnmap.html>

Pictures
RRSV symptoms:
<http://www.ricethailand.go.th/rkb/data_005/Image_Disease/rice_ragged%20stunt-05-012_B.jpg> 
and
<http://plantpro.doae.go.th/diseasegroup/rice/ragged/r_ragg25.jpg>
Brown planthoppers:
<http://www.dpvweb.net/dpv/showfig.php?dpvno=320&figno=03>
Green rice leafhoppers:
<http://www.sut.ac.th/e-texts/Agri/insectfinal2/Insects%20web/Images/chapter2_6_clip_image002.jpg>
BLB symptoms on leaves and whole plants via:
<http://www.invasive.org/browse/subject.cfm?sub=11182>
Comparison of BLB effect on resistant and susceptible cultivars:
<http://www.tari.gov.tw/tarie/photos/introduction/introduction_PPD_02.jpg>

Links
Ragged stunt disease information:
<http://www.knowledgebank.irri.org/ricedoctor/Fact_Sheets/Diseases/Rice_Ragged_Stunt.htm#top>
RRSV description and taxonomy:
<http://www.ncbi.nlm.nih.gov/ICTVdb/ICTVdB/00.060.0.09.003.htm>
RYSV description and taxonomy:
<http://www.ncbi.nlm.nih.gov/ICTVdb/ICTVdB/01.062.0.05.008.htm>  and
<http://phene.cpmc.columbia.edu/ICTVdB/01.062.0.00.347.htm>
Review of rice viruses, biology and epidemiology:
<http://arjournals.annualreviews.org/doi/abs/10.1146/annurev.phyto.34.1.249?journalCode=phyto>
Brown planthopper information:
<http://www.knowledgebank.irri.org/RiceDoctor/Fact_Sheets/Pests/Planthopper.htm#Common>
Green leafhopper information:
<http://www.knowledgebank.irri.org/RiceDoctor/Fact_Sheets/Pests/Green_Leafhopper.htm>
BLB disease information:
<http://www.knowledgebank.irri.org/RiceDoctor/Fact_Sheets/Diseases/Bacterial_Leaf_Blight.htm> 
and
<http://www.oisat.org/pests/diseases/bacterial/bacterial_leaf_blight.html>
Comprehensive BLB review:
<http://www.ias.ac.in/currsci/dec101999/REVIEWARTICLE.PDF>
Genus _Xanthomonas_ taxonomy and species list:
<http://www.bacterio.cict.fr/xz/xanthomonas.html>.  - Mod.DHA]