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[1] New Liberibacter species, tomato and potato
[2] New virus, tomato - California


[1] New Liberibacter species, tomato and potato
Date: Mon 11 Aug 2008
Source: University of California Riverside (UCR), News Release [edited]
<http://www.info.ucr.edu/cgi-bin/display.cgi?id=1903>

Bacterium linked to psyllid yellows, a tomato and potato disease

Allison Hansen, a doctoral student at UCR, has discovered a new bacterial pathogen that could be responsible for "psyllid yellows," a disease that infects and kills tomato and potato plants. The disease is spread from plant to plant by the psyllid, a sap-sucking insect.
This psyllid commonly is called potato or tomato psyllid. She named the pathogen "_Candidatus_ Liberibacter psyllaurous"; psyllaurous means psyllid yellows in Latin.

In tomato alone, psyllid yellows resulted in yield losses up to 85 percent and 50 percent in commercial tomato crops in western North America during 2001 and 2004, respectively. "The saliva of the tomato psyllid has been known to cause yellowing of tomato and potato leaves. The cause of this symptom has been a mystery for over a century. One symptom of this bacterium is yellowing of the foliage,"
said Hansen.

The discovery has the potential to help plant breeders develop resistant cultivars of potato and tomato. "We know the bacterium is vectored by the psyllid causing yellowing and death of the plant,"
Hansen said. "We're now working to confirm whether _Ca._ L.
psyllaurous is the cause of psyllid yellows."

The new bacterium is closely related to huanglongbing or HLB, also known as citrus greening disease. A huge scientific effort currently is underway to study HLB of citrus, a disease that is threatening to destroy Florida's citrus industry. "L. psyllaurous could be a good model system to come up with methods for combating citrus greening,"
Hansen said. She is trying to sequence the bacterium's genome.

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[2] New virus, tomato - California
Date: Fri 15 Aug 2008
Source: Daily Democrat, Ag Alert (California Farm Bureau Federation) report [edited] <http://www.dailydemocrat.com/business/ci_10214365>

Mysterious new tomato virus found

A new and unidentified virus has appeared in a number of processing tomato fields in northern California. This new virus looks a lot like _Tobacco streak virus_, which is fairly common in the area. But when University of California (UC) plant pathologists ran DNA tests for tobacco streak on tissue samples from these mysteriously diseased plants they came back negative. Tests for other familiar tomato viruses have also come back negative.

While this new virus has already shown up early this summer [2008] in quite a few tomato fields, it has not yet caused significant crop damage. "The virus is very widespread in our area," said Gene Miyao, UC Cooperative Extension farm adviser in the Sacramento Valley. Miyao said he first began to hear reports of the new virus in June [2008] from pest control advisers. He has since seen it or heard of it in fields in southern Colusa County, around Woodland and in the delta region of San Joaquin County.

"The symptoms on plants are an odd combination between tobacco streak and spotted wilt. Young branches have necrotic streaks beginning near the apical growth but extending 5 inches (about 13 cm) or so at times down the stem, like tobacco streak. Flower bracts on these branches often are blighted. Necrotic spotting on the new leaves appears spotted wilt-like. Fruit is without symptoms at this point. The symptoms would indicate that the problem is a virus, rather than one of the familiar soil borne fungal diseases that attack the vascular system of tomatoes," Miyao said.

A number of UC plant pathologists began trying to figure out what this ailment is. _Tobacco streak virus_ is transmitted by thrips, and this new virus may also be transmitted by thrips. Miyao said that it is unnerving not to know what the disease is, because that means no one knows how serious it could become or how it should be managed.

"Virus infected plants are more prevalent in our area this year [2008]," Miyao said. "Annually, curly top and alfalfa mosaic [viral diseases] are commonly found in local fields but at low levels." The increasing incidence of tomato viruses in the Sacramento Valley is, so far, worth noticing to make sure it does not grow into a more serious problem in the future.

[Byline: Bob Johnson]

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[A group of symptoms known as psyllid yellows has been associated with feeding by these insects and was thought to be due to the injection of toxic saliva. The presence of a new Liberibacter in plants with these symptoms has been shown in report [1] above, but proof of causation (Koch's postulates) is still being sought.
Recently, a new species of _Candidatus_ Liberibacter has been found which affects tomato and capsicum crops in New Zealand and can also be associated with zebra chip disease of potato in the USA. The tomato (or potato) psyllid _Paratrioza cockerelli_ is also suspected to be a vector. For both psyllid yellows and zebra chip there remains a possibility that similar symptoms may also be due to factors other than the Liberibacters. The relationships between the 2 new Liberibacter species and the various diseases transmitted by tomato
psyllids need to be clarified.

Only few members of _Ca._ Liberibacter have been characterised so far, including the pathogens causing citrus greening (huanglongbing, HLB). HLB is one of the most damaging diseases of citrus (further information via ProMED post no. 20080701.2006), but is limited to these crops due to the host specificity of its vector, the citrus
psyllid. In contrast, tomato psyllids have a wider host range including species in 20 plant families, and this can be expected to impact on the epidemiology and importance of the new pathogens.

Close to 20 viruses are known to affect tomato, including several new species discovered recently. Both _Tobacco streak virus_ (TSV, genus _Ilarvirus_] and _Tomato spotted wilt virus_ (TSWV, genus _Tospovirus_) are transmitted by thrips vectors (for example _Frankliniella_ and _Thrips_ species). Both TSV and TSWV can cause
considerable damage to a range of crops. Further characterisation including genomic sequencing of the new virus will be required to determine its relationship to other known tomato viruses, its host range, and its potential economic impact.

Maps
USA:
<http://www.mapsofworld.com/usa/usa-road-map-enlarge-view.html> and
<http://healthmap.org/promed?v=40,-97.6,4>
US states:
<http://www.census.gov/geo/www/us_regdiv.pdf>

Pictures
Psyllid yellows on potato plant:
<http://www.ext.colostate.edu/PUBS/INSECT/insimg/05540F04_Web.jpg>
Tomato/potato psyllids:
<http://insects.tamu.edu/images/insects/common/images/a-txt/aimg91.html> 
(adults),
<http://www.insectimages.org/browse/detail.cfm?imgnum=1327131> (immatures)
TSV symptoms on tomato:
<http://www.ipm.ucdavis.edu/PMG/T/D-TO-TBSV-FO.001.html>
TSWV symptoms on tomato:
<http://www.ag.auburn.edu/aaes/organicveg/images/clip_image002_000.jpg>
Western flower thrips:
<http://www.insectimages.org/images/768x512/4387048.jpg>

Links
Additional source for story [1]:
<http://www.sciencedaily.com/releases/2008/08/080812094532.htm>
Genus _Ca._ Liberibacter taxonomy and species list:
<http://beta.uniprot.org/taxonomy/34019>
Citrus greening data sheet:
<http://spdn.ifas.ufl.edu/EPPO_data_sheet.pdf>
Information on psyllid yellows:
<http://www.colostate.edu/programs/pestalert/vol16/1609.pdf>,
<http://www.colostate.edu/Depts/Entomology/theses/aljabr/thesis.html> and
<http://www.coopext.colostate.edu/jefferson/hort/diseases/tomatoproblems_doc.htm>
Information on tomato/potato psyllid:
<http://insects.tamu.edu/fieldguide/aimg91.html> and
<http://www.academicjournals.org/AJAR/PDF/pdf%202008/Jan/Abdullah.pdf>
_P. cockerelli_ taxonomy:
<http://zipcodezoo.com/Animals/P/Paratrioza_cockerelli.asp>
Tobacco streak disease of tomato:
<http://www.ipm.ucdavis.edu/PMG/r783102311.html>
TSWV fact sheet:
<http://vegetablemdonline.ppath.cornell.edu/factsheets/Virus_SpottedWilt.htm>
Thrips information:
<http://www.cals.ncsu.edu/course/ent425/text18/plantvectors.html>
ICTV virus taxonomy index:
<http://www.ncbi.nlm.nih.gov/ICTVdb/Ictv/index.htm>
List of some tomato viruses via:
<http://www.apsnet.org/online/common/names/tomato.asp>.  - Mod.DHA]