A
ProMED-mail post
ProMED-mail is a program of the
International Society for Infectious Diseases
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: Wed 7 August 2008
Source: Stabroek News [edited]
<http://www.stabroeknews.com/news/blast-disease-reported-in-some-rice-areas/>
Blast disease reported in some rice areas
Farmers in regions 2 and 3 have reported a moderate incidence of
blast disease in their fields, a press release from the Guyana
Rice Development Board (GRDB) said yesterday [6 Aug 2008].
The GRDB said farmers, particularly those cultivating the rustic
line, have found evidence of the disease on their farms. It said
the disease is normally prevalent in the 2nd growing season (2nd
crop) and its severity increases with distance from the tidal
flat. Areas 3-5 miles
[5-8 km] from the tidal flat or riverbank are vulnerable to the
disease "because of the high relative humidity and lack of air
movement."
Plants affected by the disease will have lesions or spots on the
leaf blade or necrotic areas on the borders of older leaves. It
may also affect the panicle -- defined by an online dictionary
as "any loose, diversely branching flower cluster" -- by
developing necrotic areas at its base which may result in no
grain set or may cause only the upper section of the panicle to
produce normal grains, depending on the time the disease
occurred.
The GRDB said too high nitrogen (urea) application rates, high
relative humidity, high plant density, prolonged overcast
conditions along with frequent drizzles or dew are all factors
that contribute to the onset and severity of the disease.
Control measures include using resistant varieties especially
during the 2nd growing season as rustic [rice] is susceptible to
the blast disease organism. Farmers can also avoid high plant
density (seed
rate) and avoid [large] quantities of nitrogen (urea)
application in a single dose on susceptible varieties. The GRDB
said chemicals
(fungicides) are also available that can provide acceptable
control of blast disease.
--
Communicated by:
ProMED-mail
<promed@promedmail.org>
[Rice blast is caused by the fungus _Magnaporthe grisea_. It is
one of the most destructive diseases of rice worldwide, often
killing the host. Yield losses of more than 50 percent are
reported in infected fields. Symptom severity and spread of the
blast fungus are influenced by climatic conditions. More than 50
species of grasses and sedges can be affected, but most strains
isolated from rice can only infect a limited number of
cultivars. 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.
For more information see links and previous posts below.
Maps
Guyana:
<http://www.guyana.org/special/gy-map-big.jpg>
Administrative regions of Guyana:
<http://www.iwokrama.org/library/gisimages/GIS_Iwokrama_GuyanaRegions.jpg>
Pictures of rice blast symptoms:
<http://www.imtech.res.in/raghava/rbpred/leaf_blast.jpg> and
<http://www.imtech.res.in/raghava/rbpred/lesion.jpg>
Links
Rice blast fact sheet (with pictures):
<http://www.knowledgebank.irri.org/ricedoctor/default.htm#Fact_Sheets/Diseases/R
ice_Blast.htm>
Information on rice blast:
<http://www.imtech.res.in/raghava/rbpred/home.html>,
<http://ascus.plbr.cornell.edu/blastdb/about.html>
_M. grisea_ taxonomy:
<http://www.indexfungorum.org/Names/SynSpecies.asp?RecordID=317113>
- Mod.DHA]
[see also in
the
archive:
Yellow mottle & blast diseases, rice - Uganda 20080504.1527
Blast disease, rice - Kenya (02): (CP) 20080421.1413 Blast
disease, rice - Kenya (CP) 20080402.1211 Virus & blast diseases,
rice - Viet Nam (Mekong Delta) 20080204.0454
2005
----
Rice blast fungus, genome sequence - China 20050424.1147
2001
----
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] |
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