A ProMED-mail post
ProMED-mail is a program of the
International Society for Infectious Diseases <http://www.isid.org>
Date: Fri 28 Sep 2012
Source: Australian Broadcasting Corporation (ABC) Rural [edited] <http://www.abc.net.au/rural/news/content/201209/s3599808.htm>
Northern rice disease not matching anything known to science
The rice disease which destroyed crops in the Kimberley's Ord Irrigation Scheme last year [2011; see ProMED-mail post 20110812.2442] is not matching any other strains of rice blast known to science.
Samples were sent to France for testing, but early results suggest the disease is either an unknown native or a mutated version.
Dr Vincent Lanoiselet, WA Department of Agriculture, says growers shouldn't be too worried, but the results have definitely surprised researchers. "The samples were not closely related to any of the more than 3000 isolates from all over the world in the reference lab. But it [the strain] could be somewhere else and just hasn't been collected, it also could be a native isolate from Australia or a re-combination of different strains.
"It is a surprise that the isolates weren't closely related to those in Indonesia or East Timor. But this doesn't mean we can't control the disease or can't work with the breeders to find a [rice] variety that will be tolerant."
Strains of rice blast exist across the world and it's estimated that an extra 60 million people could be fed if the disease didn't exist.
[Byline: Matt Brann]
[Rice blast is caused by the fungus _Magnaporthe oryzae_ (previously classified as a strain of _M. grisea_). It is one of the most destructive diseases of rice 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. 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.
Symptom severity and spread of the blast fungus are influenced by climatic conditions. The disease is also favoured by high nitrogen levels (for example from fertilizers) and high humidity. The disease 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.
The outbreak in Western Australia in 2011 was the 1st occurrence of a major outbreak of the disease in Australia (ProMED-mail post 20110812.2442). Subsequently, early in 2012 rice blast was also discovered in a trial crop in the Northern Territory (ProMED-mail post 20120217.1044294). It is not clear as yet whether the fungal strain in NT is the same as the new strain now identified in WA, whether they both may have originated from the same source, or whether the 2 outbreaks may be due to spread between the regions. None of the rice varieties tolerant or resistant to rice blast are currently available in Australia, and breeding programmes of crop varieties suitable for local conditions are being established. The majority of Australia's rice crop is grown on the east coast where the disease has not yet been detected, but a potential spread to this area is of great concern and strict quarantine regulations are in place.
Australia (with states):
<http://www.ga.gov.au/image_cache/GA4073.jpg> and <http://healthmap.org/r/3AAa> Ord River region:
Pictures of rice blast symptoms
Leaf, collar, node, and neck:
Rice blast fact sheet (with pictures):
Information on rice blast:
<http://www.cbwinfo.com/Biological/PlantPath/PyG.html> and <http://www.imtech.res.in/raghava/rbpred/home.html>
Recent updates on rice blast:
(US, Louisiana), and
<http://agfax.com/2012/07/06/32796/> (US, Texas) _M. oryzae_ taxonomy:
Blast disease, rice - Australia: (NT) 20120217.1044294 Blast disease, rice - Malaysia: (KH) 20120103.0015
Blast disease, rice - Nepal: (JU) 20111111.3339 Blast disease, rice - Australia: (WA) 20110812.2442 Blast disease, rice - Philippines: (KA) 20110801.2311 Blast disease, rice - Kenya: (CE) 20110704.2025 Rice diseases - Costa Rica, Bangladesh 20110425.1289
Blast disease, rice - Thailand: (northeast) 20101201.4315 Blast disease, rice - Taiwan: (TA) 20101115.4146 Tungro, blast, bacterial blight, rice - India: (TN, OR) 20100912.3299 Blast disease, rice - Spain: (VC) 20100906.3194 Ragged & grassy stunt viruses, rice - Thailand 20100628.2155 Multiple disease, rice - Viet Nam 20100307.0749 Blast disease, rice - Viet Nam: (Mekong Delta) 20100129.0310
Blast disease, rice - Nepal: (JU) 20090731.2682 and older items in the archives]