ProMED
http://www.promedmail.org

Source: The Financial Express [abridged, edited]
https://thefinancialexpress.com.bd/national/blast-disease-shatters-jashore-boro-farmers-dream-1618720396

Rice farmers have been shattered by blast disease in Jashore district [Khulna division], like in previous years. Blast disease [occurred] just before the ripening of paddy. [Many] farmers have been affected by cultivating BRRI-28 and Miniket rice [varieties].

Even after applying various types of pesticides, the farmers are not getting any remedy. They are being forced to cut raw paddy. [They] complained that no advice from the agriculture office was available at the moment and field officials did nothing to help them. On a visit, several fields were seen destroyed by the blast. Sporadic blast attacks have been reported [also] in other areas. The Agriculture Office was quite unaware of the blast disease.
--
Communicated by:
ProMED
<promed@promedmail.org>

[Rice blast is caused by the fungus _Pyricularia oryzae_ (previously _Magnaporthe oryzae_). It is one of the most destructive diseases of the crop worldwide, with potential yield losses of more than 50%. Symptoms include lesions on all parts of the shoot, as well as 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; infection late in the growth cycle generally leads to less severe damage. Depending on which plant parts are affected, the disease may manifest itself as leaf, collar, node, or neck blast. More than 50 species of grasses and sedges can be affected by related pathogens, but most strains isolated from rice can only infect a limited number of cultivars.

The fungus also causes wheat blast (for example, see ProMED-mail post 20210324.8267471). Although the pathogens are currently classified as the same species, the wheat blast pathogen is a distinct population (referred to as _P. oryzae_ Triticum population) and does not cause disease in rice.

Symptom severity and spread of the blast fungus are influenced by climatic conditions, including high humidity. The disease is also favoured by high nitrogen levels (for example from fertilisers). The fungus is spread by infected plant debris, mechanical means (including insect activity), water, and wind. Disease management may include fungicides and cultural practices but relies mainly on resistant varieties. Use of certified clean seed is essential, farm-saved seed poses a high risk of carry-over of the fungus to subsequent crops.

The fungus is highly variable, and this favours the emergence of new strains with increased virulence, including host resistance breaking strains. Environmental factors may also affect plant resistance. Both resistance and defense-regulator genes have been found to be involved in host resistance against blast (see links below) and could potentially be combined ("pyramided") to develop rice varieties with broad-spectrum host resistance against blast that cannot be as easily overcome by the fungus as varietal resistance based on single genes.

BRRI rice varieties have been developed by the Bangladesh Rice Research Institute (BRRI). BRRI-28 was classed as 'moderately resistant to blast' (see links below). 'Miniket' does not seem to be a specific registered rice variety, but rather merely a collective term used in the region for commercial high quality rice.

Maps
Bangladesh:
http://www.nationsonline.org/maps/bangladesh_map.jpg and
http://healthmap.org/promed/p/1049
Bangladesh divisions and districts:
http://tinyurl.com/bw2fuve

Pictures
Rice blast symptoms:
http://www.knowledgebank.irri.org/ricebreedingcourse/blast.jpg (different symptomatic forms),
https://www.dpi.nsw.gov.au/__data/assets/image/0006/798765/RiceBlast5.jpg, and
https://www.eurekalert.org/multimedia/pub/web/214166_web.jpg
Rice fields affected by blast:
http://ucanr.edu/blogs/riceblog/blogfiles/22977_original.jpg,
https://guardian.ng/wp-content/uploads/2019/06/Rice-Blast.jpg, and
https://previews.123rf.com/images/imagethink/imagethink1411/imagethink141100067/33260576-rice-blast-Stock-Photo.jpg

Links
Information on rice blast:
http://www.knowledgebank.irri.org/training/fact-sheets/pest-management/diseases/item/blast-leaf-collar (with pictures),
http://www.oisat.org/pests/diseases/fungal/rice_blast.html,
http://www.plantwise.org/KnowledgeBank/Datasheet.aspx?dsid=46103,
https://www.dpi.nsw.gov.au/biosecurity/plant/insect-pests-and-plant-diseases/rice-blast, and
http://www.imtech.res.in/raghava/rbpred/home.html
Rice blast disease cycle:
https://ars.els-cdn.com/content/image/3-s2.0-B9780123820341000086-f08-05-9780123820341.jpg and
https://www.researchgate.net/profile/Darren_Soanes/publication/7891924/figure/fig2/AS:271700617068555@1441789883887/Life-history-of-Magnaporthe-griseaa-Asexual-spores-called-conidia-germinate-and-develop.png
Research on rice blast host resistance:
https://www.sciencedirect.com/science/article/pii/S1369526618301808 (review),
https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0211061, and
https://www.researchgate.net/publication/330889038_Molecular_and_field_level_screening_for_blast_resistance_gene_donors_among_traditional_rice_varieties_of_Kerala
Impact of rice blast (and other fungal crop diseases):
http://onlinelibrary.wiley.com/doi/10.1111/j.1364-3703.2011.00783.x/full
Information on wheat blast:
http://wheatblast.org/ and
http://wheat.org/wp-content/uploads/sites/4/2016/04/Wheat-Blast-Priority-Brief-web-07Apr2016.pdf
_P. oryzae_ taxonomy and synonyms:
http://www.indexfungorum.org/names/NamesRecord.asp?RecordID=224486 and
http://www.speciesfungorum.org/Names/SynSpecies.asp?RecordID=224486
BRRI:
http://www.knowledgebank-brri.org/brri-rice-varieties.php
Profile of BRRI-28 rice variety:
http://dhcrop.bsmrau.net/brri-dhan-28/
Miniket rice:
https://www.daily-sun.com/arcprint/details/244005/Miniket-Rice:-What-Is-It-and-Why-Is-It/2017-07-29
- Mod.DHA]