A ProMED-mail post

• <http://www.promedmail.org>
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  International Society for Infectious Diseases
  <http://www.isid.org>
  
  Date: Thu 21 Jun 2018
  Source: VietnamNet [edited]
  <http://m.english.vietnamnet. vn/fms/society/202815/delta- summer-autumn-rice-planted- too-early--threatened-by- diseases.html>
  
  Farmers in the Mekong Delta who sowed the summer - autumn rice crop
  early are facing a threat of disease outbreaks. Nguyen Van Hien, Plant
  Cultivation and Protection, said [that] unfavourable weather has
  brought rice diseases which could hit yields. Diseases often occur
  when rice is sowed early or late since brown-plant hoppers and other
  pests from unharvested fields from the previous crop move to the newly
  sowed fields, he said.
  
  In Dong Thap Province some 560 ha sowed early have been affected by
  brown plant hoppers. [A farmer] said local agricultural officials did
  warn they had to have a gap of at least 3 weeks between crops to
  eliminate diseases. "But since the price of rice was high, farmers
  here sowed early."
  
  In Kien Giang Province, more than 252 140 ha have been planted, with
  15 500 ha being affected by diseases such as rice grassy stunt, rice
  ragged stunt and rice blast. 
  
  Plant Cultivation and Protection has instructed district bureaus to
  regularly report about diseases and warned farmers to destroy rice
  plants which are severely affected. This [2018] summer - autumn the
  delta has planted more than 1.65 million ha, according to the Ministry
  of Agriculture and Rural Development. 
  --
  Communicated by:
  ProMED-mail
  <promed@promedmail.org>
  
  [Rice viruses
  ------------
  _Rice ragged stunt virus_ (RRSV; genus _Oryzavirus_) has been reported
  to cause yield losses of up to 90 per cent in several Asian countries.
  Symptoms include ragged appearance of plants, twisted leaves, vein
  swelling, unfilled grains and severe stunting of plants. Its only way
  of spread is vector transmission by brown plant hoppers (BPH;
  _Nilaparvata lugens_). The insects transmit the virus in a persistent
  manner and remain infectious for life. Infected hoppers can be
  transported on air currents to spread the virus quickly over long
  distances.
  
  _Rice grassy stunt virus_ (RGSV; genus _Tenuivirus_) has been reported
  to cause serious damage in limited areas during sporadic outbreaks of
  its vector. It is spreading in large parts of the rice-growing areas
  of Asia. RGSV is also transmitted exclusively by vectors (_N. lugens_
  and other species in the genus) in the same way as RRSV. Symptoms
  include severe stunting, excessive tillering ('grassy' appearance),
  erect growth habit, leaf spots and reduced pale leaves. Infected
  plants usually survive until maturity, but produce no panicles.
  
  A number of other rice viruses (several also present in the region)
  are spread by different species of plant - or leaf hoppers. In
  tropical regions, levels of virus infection and vector density may be
  very high. High vector populations are often associated with virus
  outbreaks with crop losses of up to 100 per cent reported. In its own
  right, BPH causes yellowing, browning and drying of plants ('hopper
  burn') and leaves small injuries exposing the plant to fungal (such as
  rice blast) and bacterial infections.
  
  Disease management for these viruses includes cultural practices (such
  as short term draining of rice fields, crop rotation, or rice-free
  periods), vector control and use of cultivars with reduced sensitivity
  or resistance to the virus, the vector, or both. Crop cultivars
  resistant to BPH have low disease incidence, but insect adaptation
  overcoming plant resistance has been a problem. The application of
  insecticides to migratory plant hoppers is being used in some areas to
  reduce disease incidence.
  
  Rice blast
  ----------
  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 per
  cent. 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 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.
  
  Maps
  Viet Nam and neighbours:
  <http://www.lib.utexas.edu/ maps/middle_east_and_asia/ vietnam_pol01.jpg>
  Viet Nam provinces:
  <http://en.wikipedia.org/wiki/ File:VietnameseProvincesMap. png>
  
  Pictures
  RRSV symptoms:
  <http://farmextensionmanager. com/English/Rice%20technology% 20bank/pest%20doctor/images/ ragged%20stunt%20virus.jpg>,
  <http://eagri.org/eagri50/ PATH272/lecture01/0024.jpg> and
  <http://www.knowledgebank. irri.org/images/stories/ ragged-stunt-1.jpg>
  RGSV symptoms:
  <http://www.knowledgebank. irri.org/images/stories/rice- grassy-stunt.jpg>,
  <http://agritech.tnau.ac.in/ crop_protection/images/rice_ diseases/grassy%20stunt% 20disease.jpg>
  and
  <http://www.dpvweb.net/dpv/ showfig.php?dpvno=320&figno=04>
  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>
  Brown plant hoppers:
  <http://www.dpvweb.net/dpv/ showfig.php?dpvno=320&figno=03>
  
  Links
  Information on RRSV:
  <http://www.knowledgebank. irri.org/training/fact-sheets/ pest-management/diseases/item/ rice-ragged-stunt>,
  <https://www.plantwise.org/ KnowledgeBank/Datasheet..aspx? dsid=47647>,
  <https://www.genome.jp/ virushostdb/42475> and
  <http://sdb.im.ac.cn/vide/ descr691.htm>
  Information on RGSV:
  <http://www.knowledgebank. irri..org/training/fact-sheets/ pest-management/diseases/item/ rice-grassy-stunt>,
  <https://www.plantwise.org/ KnowledgeBank/Datasheet.aspx? dsid=47614>,
  <http://agritech.tnau.ac.in/ expert_system/paddy/ cpdisstunragg.html>
  and
  <https://www.sciencedirect. com/science/article/pii/ S0168170214001701>
  Virus taxonomy via:
  <https://talk.ictvonline.org/ taxonomy/>
  Brown plant hopper information via:
  <http://www.knowledgebank. irri.org/training/fact-sheets/ pest-management/insects/item/ planthopper>
  (with pictures)
  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: