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Published Date: 2019-11-10 22:50:50
Subject: PRO/PL> Blast & bacterial leaf blight, rice - India: (TN)
Archive Number: 20191110.6771677
BLAST DISEASE AND BACTERIAL LEAF BLIGHT, RICE - INDIA: (TAMIL NADU)
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Date: Tue 5 Nov 2019
Source: The New Indian Express [edited]
http://www.newindianexpress.com/states/tamil-nadu/2019/nov/05/rice-blast-disease-confirmed-in-nagapattinam-2057307.html


Experts have confirmed the presence of Rice Blast fungal disease in Nagapattinam district, following complaints from farmers.

Scientists spotted presence of the disease in around 20 to 30 acres with crop varieties such as 'BPT 5204'. BPT 5204 is not very disease-resistant compared to a few other varieties and is more susceptible to the disease. If it is not controlled, the [leaf spots] will expand and cause complete crop damage, scientists added.

"We found the disease in fields which were mostly waterlogged and had excess of urea fertiliser. We will conduct a case study on this and educate farmers about the disease," said the Agriculture Department. It is to note that farmers [recently] complained of lack of urea fertiliser stock in Agriculture extension centres.

The scientists also found some crops affected by 'Bacterial Leaf Blight'. They advised cow dung [fertiliser] and Pseudomonas [biocontrol agent] as a remedy.

[Byline: Antony Fernando]

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Communicated by:
ProMED-mail
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[Blast
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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 percent. 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 20170306.4883233 and 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 fertilizers). 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. However, the fungus is highly variable and this favours the emergence of new strains with increased virulence. Use of certified clean seed is essential, and farm saved seed poses a high risk of carry-over of the fungus to subsequent crops.

Leaf blight
-----------
Bacterial leaf blight (BLB) of rice is caused by _Xanthomonas oryzae_ pv. _oryzae_ (Xoo). In Asia, millions of hectares of rice paddies are severely affected every year, with reported yield losses of up to 60 percent. The pathogen causes yellowing and drying of leaves and wilting of seedlings. Blight lesions caused by severe strains elongate over the entire length of the flag leaf, giving a striped appearance. Severe strains may also affect panicles. Mild strains cause only small leaf lesions and may not lead to any detectable yield loss. Various saprophytic fungi may invade the lesions, contributing to the damage. Field patches infested with bacterial blight have a whitish, ragged appearance.

BLB is favoured by rain, high levels of fertilizer, high humidity, standing pools of water and warm temperatures. The bacterium is short-lived in soil and suspected to be seed borne 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 primary pathogen reservoirs. The disease spreads by windblown rain and mechanical means (for example when transplanting seedlings or by high insect activity).

Disease management usually includes phytosanitation (control of weed and volunteer rice reservoir hosts, removal of contaminated materials), cultural measures (optimal plant spacing and fertilizers) and use of resistant crop varieties. Control of insect populations by insecticides may help reduce the unspecific spread of bacteria via their scratching and sucking wounds. Antibacterial sprays containing antibiotics are rarely used because they often provide little benefit, and agricultural application of antibiotics is strictly regulated in most countries. The related _X. oryzae_ pv. _oryzicola_ causes bacterial leaf streak of rice.

_Pseudomonas_ spp. are ubiquitous soil bacteria. Some strains can be used as biocontrol agents of fungal and bacterial pathogens. Their biocontrol mechanisms include direct antagonism of pathogens and induction of disease resistance in the host plant.

Traditional rice cultivars previously grown in India are frequently being replaced by modern varieties. While these generally provide higher yields, some have shown a higher sensitivity to certain pathogens, for example to rice blast. For that reason, farmers were warned previously against cultivating BPT 5204 (see link below). Government departments stopped distributing the seeds and subsidies were cut, but private sources continue to supply BPT 5204 seeds.

Maps
India (with states):
http://www.mapsofindia.com/maps/india/india-political-map.htm
Tamil Nadu districts:
http://www.mapsofindia.com/maps/tamilnadu/tamilnadu-district.htm

Pictures
Rice blast symptoms:
http://www.knowledgebank.irri.org/ricebreedingcourse/blast.jpg (different symptomatic forms) and
http://www.imtech.res.in/raghava/rbpred/lesion.jpg
Rice fields affected by blast:
http://ucanr.edu/blogs/riceblog/blogfiles/22977_original.jpg and
https://previews.123rf.com/images/imagethink/imagethink1411/imagethink141100067/33260576-rice-blast-Stock-Photo.jpg
BLB symptoms on rice leaves:
http://agropedia.iitk.ac.in/sites/default/files/uas%20raichur/diseases%20of%20paddy/blb00.jpg and
http://www.knowledgebank.irri.org/images/stories/bacterial-leaf-blight-4.JPG
BLB affected rice plants:
http://www.invasive.org/images/768x512/0162037.jpg
Droplets of Xoo exudate on leaf:
http://www.invasive.org/images/768x512/0162038.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 and
http://www.imtech.res.in/raghava/rbpred/home.html
Rice blast disease cycle:
http://www.imtech.res.in/raghava/rbpred/cycle.jpg
Impact of rice blast (and other fungal crop diseases):
http://onlinelibrary.wiley.com/doi/10.1111/j.1364-3703.2011.00783.x/full
_P. oryzae_ taxonomy and synonyms:
http://www.indexfungorum.org/names/NamesRecord.asp?RecordID=224486 and
http://www.speciesfungorum.org/Names/SynSpecies.asp?RecordID=224486
BLB of rice, disease information:
http://www.knowledgebank.irri.org/decision-tools/rice-doctor/rice-doctor-fact-sheets/item/bacterial-blight,
http://www.cabi.org/isc/datasheet/56956 (with distribution map),
http://www.apsnet.org/publications/PlantDisease/BackIssues/Documents/1993Articles/PlantDisease77n01_5.pdf and via
http://www.oisat.org/pests/diseases/bacterial/bacterial_leaf_blight.html
_X. oryzae_ pv. _oryzae_ taxonomy:
http://www.uniprot.org/taxonomy/64187
BPT 5204 disease warning:
https://www.thehindu.com/news/cities/Madurai/warning-issued/article19529434.ece
_Pseudomonas_ biocontrol agents:
https://link.springer.com/chapter/10.1007/978-81-322-2647-5_15 and
https://apsjournals.apsnet.org/doi/10.1094/PHYTO-97-2-0250
Information on Indian rice varieties:
http://www.agritech.tnau.ac.in/expert_system/paddy/TNvarieties.html and
https://www.ikisan.com/ap-rice-varieties.html
- Mod.DHA

HealthMap/ProMED map available at:
Tamil Nadu State, India: http://healthmap.org/promed/p/319]

See Also

Blast disease, rice - Nigeria: (BA) 20190704.6551673
Blast disease, rice - Bangladesh: (DH) 20190506.6457423
2018
----
Blast & bacterial leaf blight, rice - Nigeria 20181029.6119130
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
2017
----
False smut & blast, rice - Bhutan, India 20171102.5419405
Blast disease, rice - India: (JK) 20170725.5202371
Blast disease, rice - Bangladesh 20170428.5000484
Bacterial leaf blight, rice - Philippines: (NS) 20170327.4927699
2016
----
Bacterial leaf blight, rice - Peru: (PI) 20160405.4138616
Bacterial leaf blight, rice - India: (TN) 20161228.4729157
Bacterial leaf blight, rice - Bangladesh: (RJ) 20161101.4598659
Bacterial leaf blight, rice - Viet Nam: (Mekong Delta) 20161014.4558824
Blast & sheath blight, rice - Philippines: (II) 20160915.4489271
Blast disease, wheat & rice - Bangladesh 20160419.4168271
Blast disease, rice - India (02): (JK) origin 20160407.4145967
Bacterial leaf blight, rice - Peru: (PI) 20160405.4138616
Blast disease, rice - India: (TN) 20160108.3918812
2015
----
Bacterial leaf blight, rice - India: (TN) 20151216.3868035
Neck blast, rice - India: (HR) 20151014.3713941
Bacterial leaf blight, rice - Bangladesh: (DA) 20151009.3702001
Blast disease, rice - Spain: (VC) 20150903.3620399
Sheath blight, rice - India: (PB) 20150831.3612426
Blast disease, rice - India: (TN) 20150128.3124545
Rice diseases - Malaysia: (western) emerging strains 20150108.3080315
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