A ProMED-mail post
ProMED-mail is a program of the
International Society for Infectious Diseases
Date: Mon 26 Jul 2021 10:38 PM
Source: Eastern Mirror Nagaland (EMN) [abridged, edited]
The Department of Agriculture has informed that blast disease of rice has been reported in Mon district [Nagaland]. Immediately after receiving a report, local agricultural officers carried out an extensive survey and spot verification in infected fields. It was found that the fields were infected with rice blast. The crops were in late tillering to panicle initiation stages.
A total of almost 1000 ha [2471 acres] are infected, constituting about 60% of the total cropping area within the affected sub-division. The incidence is 80-90% and over 1000 smallholders are affected.
[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 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; 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.
India (with states):
Rice blast symptoms:
http://www.knowledgebank.irri.org/ricebreedingcourse/blast.jpg (different symptomatic forms),
Rice fields affected by blast:
Information on rice blast:
http://www.knowledgebank.irri.org/training/fact-sheets/pest-management/diseases/item/blast-leaf-collar (with pictures),
Rice blast disease cycle:
Research on rice blast host resistance:
Impact of rice blast (and other fungal crop diseases):
Information on wheat blast:
_P. oryzae_ taxonomy and synonyms:
Blast disease, rice - Bangladesh: (KH) 20210422.8321022
Blast disease, wheat - global epidemiology 20210324.8267471
Neck blast, rice - Nepal: (CH) 20200611.7459995
Blast disease, rice - Viet Nam: alert 20200409.7202041
Blast & undiagnosed rust, wheat - Bangladesh: (RP) 20200323.7132348
Blast disease, rice - India: (TG) 20200303.7042063
Blast & bacterial leaf blight, rice - India: (TN) 20191110.6771677
Blast disease, rice - Bangladesh: (DH) 20190506.6457423
Blast & bacterial leaf blight, rice - India 20180914.6028737
Virus & blast diseases, rice - Viet Nam: (Mekong Delta) 20180712.5901134
Blast disease, rice - Bangladesh: (RJ) 20180419.5756531
False smut & blast, rice - Bhutan, India 20171102.5419405
Blast disease, rice - India: (JK) 20170725.5202371
Blast disease, rice - Bangladesh 20170428.5000484
Blast disease, wheat - India: 1st rep (WB) 20170306.4883233
Blast disease, wheat - Bangladesh: (KH) 20170123.4784298
Blast disease, wheat & rice - Bangladesh 20160419.4168271
Blast disease, rice - India (02): (JK) origin 20160407.4145967
Blast disease, rice - India: (TN) 20160108.3918812
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