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Date: April 29, 2008
Source: AllAfrica, New Vision (Kampala) report [edited]
<http://allafrica.com/stories/200804300248.html>

Dr Dennis Kyetere, the head of the Ugandan National Agricultural Research Organisation (NARO), was speaking at the inaugural meeting of the Rice Breeders Network in Kampala recently. Researchers and seed companies from over 10 African countries attended. The meeting highlighted efforts to develop and release improved disease-resistant rice varieties and overcome the barriers that prevent new varieties from reaching farmers to improve food security.

The meeting also addressed efforts to tackle diseases such as rice yellow mottle and rice blast that are devastating farmers in several regions. In Kenya recently, rice farmers lost up to half of this season's crop.

Meanwhile, Tanzania breeder Dr Nkonki Kibanda reported that the country's Department of Agricultural Services had identified local varieties resistant to rice yellow mottle virus, which can decimate 90 percent of the rice yield. Kibanda expects new disease-resistant versions of farmers' favourite variety, Supa, to be available by 2009.

[Byline: Fred Ouma, Ronald Kalyango]

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[Yellow mottle
--------------
This disease is caused by _Rice yellow mottle virus_ (RYMV, genus _Sobemovirus_, not yet assigned to family or order) and was originally confined to one district of Kenya. However, large-scale rice irrigation projects lead to build up and wide dissemination of the virus and its vectors in sub-Saharan Africa. It is now the most serious pathogen of irrigated and lowland rainfed rice in West and Central Africa, and losses of up to 100 percent have been reported.
In Uganda, RYMV-like symptoms were first observed in 2000 and presence of the virus was confirmed in 2006. From the report above, it appears to be spreading in this country.

Besides rice, the virus also affects a number of other grass species.
Symptoms include stunting, reduced tillering, mottling and yellowish streaking of the leaves, delayed flowering or incomplete emergence of the panicles and, in extreme cases, death of plants. RYMV is spread by a number of insect vectors, mainly by several species of beetles (for example _Chaetocnema pulla_). It does not appear to be seed transmitted in rice, but it can be spread by mechanical means, which is thought to account for much of its spread in the field. For example, a severe increase of RYMV incidence was noted in areas that switched rice cultivation methods from direct seeding to transplanting of seedlings. The virus survives in crop residues, and volunteer rice and grassy weeds serve as pathogen reservoirs. Disease management includes cultural practices as well as control of vectors and reservoir hosts.

RYMV is highly variable, and different strains may have different levels of virulence. Isolates originating in closely related agro-ecological zones show variability in the coat protein.
Consequently, specific resistance breeding programmes need to be carried out in different areas for local virus strains and local rice varieties. Therefore the resistant varieties reported above to be available for Tanzania may not be suitable for Uganda.

Blast disease
-------------
Rice blast is caused by the fungus _Magnaporthe grisea_. It is one of the most destructive diseases of rice worldwide with reported losses of more than 50 percent in infected fields. Symptoms include lesions on all parts of the shoot, stem rot, and panicle blight. When nodes are infected, all plant parts above the infection die and yield losses are severe. When infection occurs at the seedling or tillering stages, plants are often completely killed. More than 50 species of grasses and sedges can be affected by different strains of the fungus, but most strains isolated from rice can only infect a limited number of cultivars.

Symptom severity and spread of the blast fungus are influenced by climatic conditions. The disease is spread by infected plant debris, mechanical means, water, and wind. Disease management may include fungicides and cultural practices, but relies mainly on resistant varieties. The fungus is highly variable, however, and new strains are emerging, breaking down host resistance.

The report above refers to the serious outbreak of rice blast, which is currently being reported from Kenya (see previous ProMED-mail posts 20080402.1211 and 20080421.1413). A loss of 10 to 20 percent of the annual national rice crop is estimated as a result of this outbreak, which has been attributed largely to heavy rains, poor cultural practices, and infected rice seed.

Maps
Uganda:
<http://unimaps.com/uganda/mainmap.gif> and <http://healthmap.org/promed?v=1.3,32.4,6>
African countries:
<http://worldatlas.com/webimage/countrys/africa/maps/africa.htm>

Pictures
RYMV symptoms:
<http://www.innovations-report.de/bilder_neu/70653_Unbenannt-1.jpg>  and <http://www.ird.fr/fr/imagesTEST/34971.jpg>
_C. pulla_ RYMV vector:
<http://www.dpvweb.net/dpv/showfig.php?dpvno=149&figno=05>
Rice blast symptoms:
<http://www.imtech.res.in/raghava/rbpred/lesion.jpg>,

Links
Information on RYMV:
<http://www.warda.org/publications/AR2000/F3.pdf>
Research on RYMV host resistance and epidemiology:
<http://www.innovations-report.de/html/berichte/agrar_forstwissenschaften/bericht-70653.html>,
<http://www.agbioforum.org/v7n12/v7n12a06-datta.htm> and via <http://www.warda.org/africa-rice-congress/presentations.html>
Detection and transmission of RYMV:
<http://library.wur.nl/wda/dissertations/dis3747.pdf>
RYMV strains:
<http://www.springerlink.com/content/2lja0tcu3dc27qwb/>
RYMV taxonomy:
<http://www.ncbi.nlm.nih.gov/ICTVdb/ICTVdB/00.067.0.01.005.htm>
Rice blast fact sheet (with pictures):
<http://www.knowledgebank.irri.org/ricedoctor/default.htm#Fact_Sheets/Diseases/Rice_Blast.htm>
Information on rice blast:
<http://www.imtech.res.in/raghava/rbpred/home.html>,
<http://ascus.plbr.cornell.edu/blastdb/about.html>, and _M. grisea_ taxonomy:
<http://www.indexfungorum.org/Names/SynSpecies.asp?RecordID=317113>.  - Mod.DHA]

[see also in the archive:
Blast disease, rice - Kenya (02): (CP) 20080421.1413 Blast disease, rice - Kenya (CP) 20080402.1211 Rice yellow mottle virus - Gambia: 1st rep. 20080208.0507 Virus & blast diseases, rice - Viet Nam (Mekong Delta) 20080204.0454
2006
----
Rice yellow mottle virus - Uganda: 1st report 20060427.1221
2005
----
Rice blast fungus, genome sequence - China 20050424.1147
2001
----
Rice yellow mottle virus, rice - Africa (Central) 20010806.1857 Magnaporthe grisea, rice blast - Vietnam 20010214.0298 2000
----
Rice blast: new method of control (02) 20000928.1678 Rice blast: new method of control 20000825.1419
1998
----
Rice blast - USA (California) 19980224.0361
1997
----
Emergence of plant diseases 19970305.0493]