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[1] _Ca._ L. psyllaurous - Mexico: 1st report
[2] _Ca._ L. solanacearum - USA, Mexico, Guatemala: epidemiology
[3] Liberibacter and psyllid vectors - New Zealand: economic
impact
******
[1] Candidatus Liberibacter psyllaurous - Mexico: 1st
report
Date: May 2009
Source: Plant Disease [edited]
<http://apsjournals.apsnet.org/doi/abs/10.1094/PDIS-93-5-0552A>
[ref: JE Munyaneza, et al. First report of '_Candidatus_
Liberibacter psyllaurous' in potato tubers with zebra chip
disease in Mexico. Plant Dis 2009; 93(5): 552; DOI:
10.1094/PDIS-93-5-0552A]
Zebra chip (ZC), an emerging disease of potato (_Solanum
tuberosum_ L.) first documented in potato fields around Saltillo
in Mexico in 1994, has been identified in the south western
United States, Mexico, and Central America and is causing losses
of millions of dollars to the potato industry. Recently, this
damaging potato disease was also documented in New Zealand. This
disease is characterized by a striped pattern of necrosis in
tubers produced on infected plants, and fried chips processed
from these infected tubers are commercially unacceptable.
Recent studies conducted in the United States and New Zealand
have associated ZC with a new species of '_Candidatus_
Liberibacter' vectored by the potato psyllid, _Bactericera
cockerelli_ Sulc. A bacterium designated '_Candidatus_
Liberibacter psyllaurous' has recently been identified in potato
plants with "psyllid yellows" symptoms that resemble those of
ZC.
To investigate whether liberibacter is associated with ZC in
Mexico, 11 potato (cv. Atlantic) tuber samples exhibiting strong
ZC symptoms and six asymptomatic tubers were collected from a
ZC-affected commercial potato field near Saltillo City,
Coahuila, Mexico in September 2008 and tested for this bacterium
by PCR. 7 of 11 (63.7 per cent) ZC-symptomatic tubers and one of
6 (16.7 per cent) asymptomatic potatoes yielded the expected
1168 bp [basepair] 16S rDNA and 669 bp amplicons, indicating the
presence of liberibacter.
Amplicons were sequenced and showed 100 per cent identity to
liberibacter 16S rDNA sequences amplified from potato psyllids
from Texas and potato tubers from Kansas. The ZC 669 bp sequence
was 98 per cent identical to liberibacter ribosomal protein gene
sequences amplified from several solanaceous plants in New
Zealand. The 1168 bp sequence was also identical to the 16S rDNA
sequence of '_Ca._ Liberibacter psyllaurous'.
To our knowledge, this is the first report of '_Ca._
Liberibacter psyllaurous' associated with ZC-affected potatoes
in Mexico.
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[2] Candidatus Liberibacter solanacearum - USA, Mexico,
Guatemala: epidemiology
Date: June 2009
Source: Plant Disease [edited]
<http://apsjournals.apsnet.org/doi/abs/10.1094/PDIS-93-6-0574>
[ref: GA Secor, et al. Association of '_Candidatus_
Liberibacter solanacearum' with zebra chip disease of potato
established by graft and psyllid transmission, electron
microscopy, and PCR. Plant Dis 2009; 93(6):
574-583; DOI: 10.1094/PDIS-93-6-0574]
A new disease of potatoes, tentatively named zebra chip (ZC)
because of the intermittent dark and light symptom pattern in
affected tubers which is enhanced by frying, was first found in
Mexico in 1994 and in the south western United States in 2000.
The disease can cause severe economic losses in all market
classes of potatoes. The cause of ZC has been elusive, and only
recently has been associated with a '_Candidatus_ Liberibacter'
species.
Field samples of potato plants were collected from several
locations in the United States, Mexico, and Guatemala to
determine transmission to potato and tomato by grafting of
ZC-infected scions and psyllid feeding. The disease was
successfully transmitted, through up to 3 generations, by
sequential top- and side-grafting ZC-infection scions to several
potato cultivars and to tomato. The disease was also
successfully transmitted to potato and tomato plants in
greenhouse experiments by potato psyllids collected from potato
plants naturally affected with ZC.
Transmission electron microscopic observation of ZC-affected
tissues revealed the presence of bacteria-like organisms (BLOs)
in the phloem of potato and tomato plants inoculated by grafting
and psyllid feeding. The BLOs were morphologically similar in
appearance to BLOs associated with other plant diseases.
Polymerase chain reaction (PCR) amplified 16S rDNA sequences
from samples representing different geographic areas, including
the United States, Mexico, and Guatemala, were almost identical
to the 16S rDNA of '_Ca._ L. solanacearum' previously reported
from solanaceous plants in New Zealand and the United States.
Two subclades were identified that differed in 2 single
base-pair substitutions. These data confirm the association of
'_Ca._ L. solanacearum' with potatoes affected by ZC in the
United States, Mexico, and Guatemala.
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[3] Liberibacter and psyllid vectors - New Zealand: economic
impact
Date: Tue 12 May 2009
Source: Manawatu Standard [edited]
<http://www.stuff.co.nz/manawatu-standard/rural/2404206/New-pest-wrecking-potato-crop>
New pest wrecking potato crop
The jury is still out on the impact a new pest, the potato
psyllid, will have on crop yields. The insect spreads a damaging
bacterium, liberibacter.
Horticulture New Zealand's Potato Group chairman Terry Olsen
said information from potato growers suggested the psyllid has
had between a 10 and 20 per cent impact on lowering potato
yields, but not a lot is known about the insect's influence yet.
"It is a very new pest here. In 2008, we saw it first and it has
become widespread since then," Mr Olsen said.
"There is some uncertainty and concern about next year's crop."
The insect lives on solanaceous plants, which included tomatoes,
capsicums, and potatoes. Solanaceous weeds and volunteer potato
plants are likely to be reservoirs between potato crop cycles.
Mr Olsen said after talking to other growers, it looked as
though crops harvested early in the season largely escaped
damage, while those brought in since late April [2009] have
shown psyllid impact.
"There is a lot of research going on, but as yet, we don't have
a good fix on the psyllid in New Zealand. There is early
evidence that it may thrive in warmer climates and those that
have mild winters," he said. "I think the answer will be a
management package, rather than the use of agri-chemicals alone.
There are also some indications that some varieties are more
resilient to the psyllid than others," he said.
Mr Olsen believed while research study was likely to help in the
longer term, most early information would come from grower
observation. "The impact of the psyllid is still an unknown and
so is the insect. At this stage we just don't know the enemy
well enough," Mr Olsen said.
[byline: Jill Galloway]
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[Zebra chip (ZC) disease of potato was first reported in Mexico
in 1994 and has caused yield losses of up to 60 per cent in
Guatemala, Mexico, and the southwestern USA. Symptoms include
early senescence of plants and necrotic flecking of tubers where
starch is converted to soluble sugars. This results in
zebra-like stripes and brittleness during processing. ZC leaf
symptoms also resemble a group of symptoms known as psyllid
yellows (PY) which was thought to be due to the injection of
toxic saliva by the feeding insects.
A new liberibacter species transmitted by potato (or tomato)
psyllids (_Bactericera cockerelli_) has now been found to be
associated with ZC and PY. The finding in item 1 that the
liberibacter was present in one asymptomatic tuber does not
contradict this, because it may, for example, be due to an early
stage of infection before visible symptoms. The experimental
transmission studies in item 2 have fulfilled Koch's postulates
(a set of criteria for establishing a causal relationship)
showing infectiousness of the new pathogen. In New Zealand,
where the potato psyllid was first reported in 2006, the new
liberibacter has been found to affect also tomato and capsicum.
There appears to be some dispute about naming the species with
both _Ca._ L. psyllaurous and _Ca._ L.
solanacearum used above as preliminary names.
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-mail post no.
20090415.1436), but is limited to these crops due to the host
specificity of its vector, the citrus psyllid. In contrast,
potato psyllid has 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 pathogen.
For both ZC and PY there remains a possibility that similar
symptoms may also be due to factors other than the liberibacter.
A possible role of phytoplasmas remains to be clarified which
were previously reported as the cause of ZC in some areas, but
not in others.
Maps
Mexico:
<http://www.mexico.us/map.htm>
and
<http://healthmap.org/r/009U>
Mexican states:
<http://www.lib.utexas.edu/maps/americas/mexico_pol97.jpg>
North and Central America:
<http://www.worldatlas.com/webimage/countrys/na.htm>
<http://www.census.gov/geo/www/us_regdiv.pdf>
<http://healthmap.org/r/009V>
New Zealand
<http://www.backpack-newzealand.com/images/new-zealand-map.gif>
and <http://healthmap.org/r/00c3>
Pictures ZC/psyllid yellows affected potato plants:
<http://www.forestryimages.org/images/3072x2048/1490010.jpg>
and <http://www.ext.colostate.edu/PUBS/INSECT/insimg/05540F04_Web.jpg>
ZC and healthy potato tubers:
<http://www.digitaljournal.com/img/4/2/9/0/i/4/1/7/o/8ab1aa702fece1872973ac17aec85b6f.jpg>
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) Links Information on potato zebra chip disease:
<http://www.panhandle.unl.edu/pdf/potato_eyes_march07.pdf>
(with pictures), <http://www.digitaljournal.com/article/257488>,
and <http://www.mysanantonio.com/business/stories/MYSA030807.1E.zebrachip.2e4dbdf.html>
Information on psyllid yellows:
<http://www.colostate.edu/programs/pestalert/vol16/1609.pdf>
and <http://www.coopext.colostate.edu/jefferson/hort/diseases/tomatoproblems_doc.htm>
Information on potato psyllids:
<http://www.crop.cri.nz/home/insect-watch/>
and <http://insects.tamu.edu/fieldguide/aimg91.html>
Recent research on new liberibacters from solanaceous crops:
<http://www.sciencedaily.com/releases/2008/08/080812094532.htm>,
<http://apsjournals.apsnet.org/doi/abs/10.1094/PDIS-92-10-1474A>,
<http://apsjournals.apsnet.org/doi/abs/10.1094/PDIS-93-5-0551B>,
and <http://apsjournals.apsnet.org/doi/abs/10.1094/PDIS-93-3-0208>
Genus _Ca._ Liberibacter taxonomy and species list:
<http://beta.uniprot.org/taxonomy/34019>
Citrus greening data sheet:
<http://www.eppo.org/QUARANTINE/bacteria/Liberobacter_africanum/LIBESP_ds.pdf>.
- Mod.DHA]
[see also
in the
archive:
2008
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Novel pathogens, tomato, potato - USA 20080820.2593
Liberibacter, solanaceous crops - New Zealand, USA 20080725.2269
Liberibacter, tomato & capsicum - New Zealand: new pathogen
20080604.1781
2007
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Zebra chip disease, potato - USA: research 20070530.1751] |
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