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Bacterial leaf blight on rice in Bangladesh

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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: April 14, 2008
Source: UN Integrated Regional Information Networks (IRIN) [edited]
<http://www.irinnews.org/Report.aspx?ReportId=77752>

Over the past week the retail price of rice has held steady. But in Dhaka long queues continued outside government open market sales centres. Although this month's [April 2008] 'boro' rice harvest, which accounts for some 60 percent of the country's yield, is expected to be a bumper one, severe crop losses as a result of monsoon floods last year [2007], coupled with a devastating cyclone, have helped keep stocks low.

Bacterial leaf blight (BLB), a serious rice disease, also poses a threat to stocks, but agriculture adviser CS Karim was optimistic this week, saying 'boro' production would exceed the target this year [2008] thanks in part to proper remedial measures having been taken.
His optimism was echoed by researchers and agricultural experts at Bangladesh Agricultural University who said the BLB outbreak in many areas would probably not cause extensive damage to the 'boro' yield.

However, Bangladesh's is far from being out of the woods, with government officials predicting the "crisis" likely to last quite some time. "Bangladesh could have a food surplus if different rice strains were grown properly. Good seeds, good plants, balanced growth of crops, and efficient irrigation at the right time can produce 6 to
7 metric tonnes of food grains per hectare," MA Hamid, a scientist at the International Rice Research Institute [IRRI], said.

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Communicated by:
ProMED-mail
<promed@promedmail.org>

[Bacterial leaf blight (BLB) of rice is caused by _Xanthomonas oryzae_ pv. _oryzae_ (previously _X. campestris_ pv. _oryza_). It was first noticed in Japan in 1884 and has since been reported from Asia, northern Australia, Africa, and the USA. The pathogen causes yellowing and drying of leaves, wilting of seedlings, and reduces yield. In Asia, millions of hectares of rice paddies are severely affected every year with reported yield losses of up to 60 percent.

Blight lesions caused by severe strains of the bacterium elongate over the entire length of the flag leaf, giving a striped appearance to leaves. Lesions caused by mild strains are usually only a few centimeters long. Mild strains may not cause any detectable yield loss. Various saprophytic fungi may invade the lesions, contributing to the damage. Panicles may also be infected by severe strains. Field patches infested with bacterial blight have a whitish, ragged appearance.

The bacterium is short-lived in soil and suspected to be seedborne, but also to be short-lived in seeds. Grassy weeds, infected plant material, such as rice stubble or ratoons, and contaminated irrigation systems are thought to be the primary pathogen reservoirs.
The disease spreads by windblown rain and mechanical means (for example when transplanting seedlings) and is favoured by rain, high levels of fertiliser, high humidity, standing pools of water, and temperatures above 25 deg C (77 deg F).

Boro rice is an irrigated, high-yielding, cold-tolerant, relatively pest-free, and photoperiod-insensitive rice cultivated during the winter months in India and Bangladesh. Other types of rice grown in the region are 'amon' and 'aus'. In addition to BLB, these have been reported to be currently affected in Bangladesh by other diseases as well (see ProMED-mail post no. 20071030.3524). Recent outbreaks of BLB have also been reported from India and Pakistan (see previous ProMED-mail posts listed below).

Maps
Bangladesh:
<http://www.lib.utexas.edu/maps/middle_east_and_asia/bangladesh_pol96.jpg>  and <http://healthmap.org/promed?v=23.8,90.3,5>
Districts and cities:
<http://www.mapsofworld.com/bangladesh/bangladesh-political-map.html>

Pictures
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
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>
Information on rice diseases, including BLB:
<http://msucares.com/pubs/publications/p1840.htm>
Genus _Xanthomonas_ taxonomy and species list:
<http://www.bacterio.cict.fr/xz/xanthomonas.html>
Details of rice varieties:
<http://dacnet.nic.in/rice/Rice%20Varieties%20-%2008.htm>
Bangladesh Rice Research Institute:
<http://brri.gov.bd/>
IRRI:
<http://www.irri.org>. - Mod.DHA]

[see also in the archive:
2007
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Rice diseases - Bangladesh 20071030.3524 Bacterial leaf blight, rice - Pakistan (Sindh, Punjab) 20071005.3293 Bacterial leaf blight, rice - India (Punjab) 20070824.2775
2005
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Flag smut, bacterial leaf blight, rice - India (Punjab & Haryana) 20050927.2841]
 



 

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