A ProMED-mail post
<http://www.promedmail.org>
ProMED-mail is a program of the
International Society for Infectious Diseases <http://www.isid.org>

Date: Wed 24 Jul 2008
Source: 3 News New Zealand [edited] [LINK]

Mystery bacteria found in New Zealand linked to potato disease in the US

A plant disease scare in tomatoes, which triggered biosecurity bans on New Zealand potatoes, tomatoes, and capsicums, has now been linked to a disease in American potato crops. And the potato disease, known as "zebra chip," has now been discovered in an Auckland spud crop, NZPA (New Zealand Press Association) has been told.

The disease-causing bacterium disrupted New Zealand exports last month [June 2008] when agriculture authorities revealed its discovery in 3 Auckland commercial hothouses in January [2008]. The announcement by NZ scientists that it was a previously unrecorded species of _Candidatus_ Liberibacter spooked some key export customers, as it is related to huanglongbing disease -- also known as citrus greening.

But now the Ministry of Agriculture and Forestry (MAF) has told growers that DNA tests developed in New Zealand show that the bacterium is in Texan potato crops, and is probably the cause of "zebra chip" disease which has been hitting American crops for years.
"The Liberibacter detected in the USA is the same species as that detected in NZ," a MAF spokeswoman told NZPA.

Zebra chip converts part of the starch in a potato to soluble sugar, and when the potato is cooked, causes zebra-like stripes and breaks up the chip. Spread by potato psyllids -- scientifically known as _Bactericera cockerelli_ -- the disease is thought to have been introduced to the US 15 years ago from Central America. The insect also turned up in New Zealand -- found in an Auckland greenhouse in
2006 -- and has since dispersed as far south as Nelson. Zebra chip is a serious problem in regions such as Texas, particularly on varieties used for manufacture of french fries.

MAF said it had provided American researchers with genetic markers for the bacteria and 2 laboratories detected it in Texas in potatoes showing zebra chip symptoms. The US has not reported the bacteria causing problems in tomatoes. The identification means that trade officials re-negotiating access for NZ fruit and vegetables to overseas markets are no longer dealing with an unknown disease -- they have been able to tell customer countries that the bacteria is probably the cause of zebra chip.

MAF said that after the announcement that the mystery bacterium was likely being spread by potato psyllids, it was first told of zebra chip symptoms in domestic potato crops. Symptoms resembling zebra chip showed up in potatoes harvested from a breeding trial in South Auckland in May [2008]. "These potato tubers tested positive for Liberibacter and was our 1st report of such in potatoes in NZ," the MAF spokeswoman said. American experts said that controlling the potato psyllids and planting seed potatoes certified free of zebra chip can reduce the spread.

--
Communicated by:
ProMED-mail
<promed@promedmail.org>

[This is a very exciting discovery linking 2 unsolved disease problems.

The new species of _Candidatus_ Liberibacter has been found to affect growth, quality, and yield of tomato and capsicum crops in New Zealand. Symptoms have been detected in both leaves and fruit and may vary across varieties and growing conditions. The tomato (or potato) psyllid _Paratrioza (Bactericera) cockerelli_ was suspected to be a vector of the new Liberibacter species in NZ.

Zebra chip (ZC) has been both economically and scientifically important in the US. A stolbur-like phytoplasma was reported as the primary cause of ZC in some areas, but to have only a minor role in others. Generally, symptoms are not a reliable means of diagnosis of plant pathogens. Similar diseases can be caused by different organisms; there may be co-infections or disease syndromes involving additional factors. ZC was suspected to have the potential of being linked to a new pathogen, and it has now been shown that the new Liberibacter can be associated with ZC symptoms.

The occurrence of this new pathogen in 2 such distinct areas would suggest that it may be present in other regions of the world as well.
Its discovery is particularly significant because only a few members of _Ca._ Liberibacter have been characterised so far. The genus includes the pathogens causing citrus greening (huanglongbing, HLB), which is one of the most damaging diseases of citrus crops in different parts of the world. HLB is transmitted by citrus psyllids, which feed only on citrus species. In contrast, tomato psyllids have a rather wide host range including species in 20 plant families, and this can be expected to impact on the epidemiology and importance of the new pathogen.

Maps
USA:
<http://www.mapsofworld.com/usa/usa-road-map-enlarge-view.html> and
<http://healthmap.org/promed?v=40,-97.6,4>
New Zealand
<http://www.backpack-newzealand.com/images/new-zealand-map.gif> and
<http://healthmap.org/promed?v=-42.4,172.7,5>

Pictures
ZC tuber symptoms:
<http://www.ars.usda.gov/is/pr/2007/071026ZebraChip-i.jpg> and <http://newagnews.tamu.edu/dailynews/stories/ENTO/photos/0219ZebraChipRoda-lr.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)

Links
Media release and description of tomato symptoms in NZ:
<http://www.scoop.co.nz/stories/SC0806/S00004.htm>
Information on zebra chip disease:
<http://www.panhandle.unl.edu/pdf/potato_eyes_march07.pdf>
Study on economic impact of ZC:
<http://cnas.tamu.edu/Zebra%20Chip%20Impacts%20Final.pdf>
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>
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>. - Mod.DHA]