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Neck blast on rice in Nepal


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: Sun 7 Jun 2020

Source: The Kathmandu Post [abridged, edited] <https://kathmandupost.com/money/2020/06/07/neck-blast-disease-destroys-chitwan-s-spring-paddy-crop>

The standing spring paddy crops in east Chitwan [district, Province Three] have been afflicted by neck blast, which causes the grain to shrivel. This problem has been seen all over east Chitwan.

Farmers began planting varieties like Hardinath-1, Gheupuri, and PR in mid-March [2020]; 70% of the farmers plant Hardinath-1, and the outbreak occurred in fields that were planted with it. Hardinath-1 is a Nepali hybrid variety, and the crop acreage has increased in recent years. The variety is not only very productive, it can also withstand hail and wind better.

Last year [2019] too, this paddy variety had been afflicted with neck blast. But farmers still planted [it] this year [2020] because of its high yield. [It is estimated that] more than 50% of the crops would be damaged due to the neck blast.

[Byline: Ramesh Kumar Poudel]

--

Communicated by: ProMED-mail <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 posts
http://promedmail.org/post/20170306.4883233 and http://promedmail.org/post/20170123.4784298). 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. 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.

 

Maps

Nepal:

<http://www.lib.utexas.edu/maps/middle_east_and_asia/nepal_pol90.jpg>

Nepal provinces and districts:

<http://ncthakur.itgo.com/map15.htm> and <https://www.arcgis.com/sharing/rest/content/items/5625cbcb6b32420d9afb197450a238fc/resources/1574594769906.jpeg>

 

Pictures

Rice blast symptoms:

<http://www.knowledgebank.irri.org/ricebreedingcourse/blast.jpg>

(different symptomatic forms),

<https://impb.ethz.ch/research/research-nkb/resistancessources/_jcr_content/par/fullwidthimage/image.imageformat.lightbox.435463652.jpg>,

<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>,

<https://impb.ethz.ch/research/research-nkb/resistancessources.html>

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>

- Mod.DHA]

 

[See Also:

Blast disease, rice - Viet Nam: alert

http://promedmail.org/post/20200409.7202041

Blast disease, rice - India: (TG)

http://promedmail.org/post/20200303.7042063

2019

----

Blast & bacterial leaf blight, rice - India: (TN)

http://promedmail.org/post/20191110.6771677

Blast disease, rice - Bangladesh: (DH)

http://promedmail.org/post/20190506.6457423

2018

----

Blast & bacterial leaf blight, rice - India

http://promedmail.org/post/20180914.6028737

Virus & blast diseases, rice - Viet Nam: (Mekong Delta)

http://promedmail.org/post/20180712.5901134

Blast disease, rice - Bangladesh: (RJ)

http://promedmail.org/post/20180419.5756531

2017

----

False smut & blast, rice - Bhutan, India

http://promedmail.org/post/20171102.5419405

Blast disease, rice - India: (JK)

http://promedmail.org/post/20170725.5202371

Blast disease, rice - Bangladesh

http://promedmail.org/post/20170428.5000484

Blast disease, wheat - India: 1st rep (WB)

http://promedmail.org/post/20170306.4883233

2016

----

Blast disease, wheat & rice - Bangladesh

http://promedmail.org/post/20160419.4168271

Blast disease, rice - India (02): (JK) origin

http://promedmail.org/post/20160407.4145967

Blast disease, rice - India: (TN)

http://promedmail.org/post/20160108.3918812

and additional items in the archives]



More news from: ISID (International Society for Infectious Diseases)


Website: http://www.isid.org

Published: June 12, 2020

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