Zebra Chip A challenging disease of potato

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					Zebra Chip: A challenging
disease of potato


            Gary Secor
    North Dakota State University
             Fargo, ND
What is Zebra Chip?
It’s a new disease of potato, first observed in
.
   Mexico in 1994


The disease
was first noticed
as darkened
stripes in potato
chips
 Spread to the US – (2000)
 States with confirmed cases of
Zebra Complex:
       Texas, California, Kansas,
     Nebraska, New Mexico,
     Colorado
       Also confirmed in Guatemala
     and possibly in Honduras
 All crops impacted – seed, table
stock as well as all processing




                                     States with Zebra Complex



                                                                 G. Bester. Frito Lay
Tuber Symptoms of ZC
 Discoloration of medullary rays
 ranging from mild to severe and
 can affect the entire length of the
 tuber; this is the diagnostic
 symptom
Foliar Symptoms of ZC
                 Swollen Nodes
                 Aerial tubers
                 Zigzag stems
                                 Leaf curl
                                 Purple top-like




         Scorching
         Wilt
ZC has not been reported in any seed
production area and appears to be independent
of seed source
  Frequently kills the eyes, or produces weak plants
  There is evidence of some plants with ZC symptoms
  growing from ZC seed tubers (Gudmestad, 2006)
Present in volunteer Red LaSoda in TX, 2005
All cultivars appear susceptible; both chip and
tablestock cultivars
Field remission of symptoms by tetracycline
Transmission
Grafting
  ZC disease has been
  reproduced by graft
  transmission from
  multiple samples from
  TX and MX
    Typical symptoms
    Multiple generations
  Also grafted to tomato
    Symptoms resemble
    “Permanente del tomate”
Grafted to tomato   Grafted back to potato
                    produces ZC symptoms




                           (IM Lee)
Permanente del tomate . Courtesy J Garzon.
 Psyllid
 transmission
Transmission of ZC
by potato psyllid
  One greenhouse test
  at NDSU
  J. Munyaneza, USDA-
  ARS




                        Psyllid Transmission
Dissemination

Scattered plants or
small clusters in the
field
In 2005, extensive
areas of ZC in some
fields
Appears to have an
airborne vector
  Row cover removal trials
  prevent infection
                                Row Cover Trial
                                    Guatemala 2004

                        12
                                                                  AGRIL
                                                                  AGRIBON
Percent Plant with ZC




                        10

                         8

                         6

                         4

                         2

                         0
                        4/22/2004      5/22/2004      6/22/2004             7/22/2004
                                           Cover removal date
Few or no aster LH,
beet LH, sharpshooters
or aphids have been
detected in ZC fields
Only potato psyllid
Bactericera (Paratrioza)
cockerelli has been
consistently associated
with ZC disease in all
areas
Psyllid yellows is
different than ZC
  Foliar symptoms similar,
  tuber symptoms different
Etiology
 While symptomatology suggests phytoplasma as a cause
    Phytoplasma have been detected in plants with similar foliar
    symptoms; but phytoplasmas are not consistently associated with
    ZC
    However a new phytoplasma, Phytoplasma americanum has
    been associated with ZC like symptoms in NE
 However, four phytoplasmas have been found associated with
 purple top in US and Mexico, but not associated with ZC
    Aster yellows (16SrI)
    Clover proliferation (16SrVI); also potatoes in Pacific NW USA
    A new phytoplasma Candidatus Phytoplasma americanum (16
    SrXII)
    Mexican periwinkle virescense (16 SRXIII)
Neither viruses nor viroids are associated
with Zebra Chip symptoms
All attempts to isolate plant pathogenic fungi
and bacteria from symptomatic tissue have
failed, including Xylella fastidiosa.
Transmission Electron
Microscopy of Symptomatic
Tissue
Note bacteria-
like entities in
phloem
Scanning Electron Microscopy of
Symptomatic Tissue




                        Note bacteria-like
                        entities in phloem
Could Zebra Chip be caused
by a BLO ?
 BLO = bacteria-like organism.

 BLOs are non-culturable, phloem restricted
 prokaryotes that cause several plant
 diseases.
Plant Diseases caused by
Phloem-restricted BLOs
Cucurbit yellow vine disease
  Etiology: unique strain of Serratia marcescens (γ3 subgroup)
  Vector: squash bug (Anasa tristis)


Marginal chlorosis of strawberry
  Etiology: Ca. Phlomobacter fragariae (γ3 subgroup)
  Vector: cixiid (Cixius wagneri)


Basses richesses of sugar beet
  Etiology: unnamed γ3 proteobacterium
  Vector: planthopper (Pentastiridius spp.)
More Plant Diseases caused
by Phloem-restricted BLOs
 Citrus huanglongbing
  Etiology: Ca. Liberibacter asiaticum, L. africanum,
  L. americanus (α2 subgroup)
  Vector: psyllids (Trioza erytreae, Diaphorinia citri)


 Papaya bunchy top
  Etiology: Rickettsia spp. (α1 subgroup)
  Vector: leafhoppers (Empoasca papayae, E.
  stevensi)
PCR to detect phloem-
restricted BLOs

 Primers of known BLO’s
 Application of primers to ZC DNA extracts
   Fra4/Fra5 – variable results, not the expected 550
   bp fragment
   YV1/YV2 – the expected 640 bp fragment
Amplicons generated by PCR from
ZC template with YV1/YV2 primers
Cloning and sequencing of
YV1/YV2 amplicon - PEI
 Homology of 8 clones to GenBank
 sequences:
   5 clones were identical to one another and
   showed 98-99% homology with a plant-
   associated enterobacter with similarities to
   Erwinia rhapontici.
   2 clones shared 100% homology with an
   unculturable bacterium from the midgut of
   cabbage white butterfly.
   1 clone was homologous to a ribosomal gene
   fragment of a bacterium found in raw milk.
Cloning and sequencing of YV1/YV2
amplicon – NDSU
Clone      Location       Best match (% homology)
621-2L1    Texas          Uncultured bact., white cabbage butterfly (99%)
621-2L2    Texas          Uncultured bact., white cabbage butterfly (99%)
664-L1     Pearsall, TX   Serratia marcescens (97%)
664-L2     Pearsall, TX   Serratia marcescens (97%)
677-18L1   Mexico         Pantoea agglomerans (98%)
677-18L2   Mexico         Pantoea agglomerans (98%)
695-CT1    Dalhart, TX    Erwinia rhapontici (98%)
695-CT2    Dalhart, TX    Serratia marcescens (100%)
710-16St1 Guatemala       Pectobacterium carotovorum (99%)
710-16St2 Guatemala       Pectobacterium carotovorum (99%)
Cloning and sequencing of YV1/YV4
and A79 amplicons
  Mello and Fletcher - OkSU
  Samples from Pearsall, TX 2007
    Foliar and tuber samples with phloem necrosis
  Unable to culture Serratia marcescens

 YV1/YV2 all S. marcescens strains
 YV1/YV4 Specific to Serratia spp
 A79 Specific to CYVD strains
Primer        Sample 1           Sample 2         Sample 3        Sample 4

YV1/YV2 1 Sm (98%)          1 Sm (98%)
        2 uncult bact (98%) 2 uncult bact (98%)
        3 mosquito (97%)    3 mosquito (97%)
A79                                               1 Sm (95%) 1 Sm (98%)
                                                             3 Rhodobacter (92%)
VY1/VY2 primers set sent to J. Garzon
amplified bands from ZC potatoes collected
near Saltillo, MX
Similarities of Zebra Chip Disease with
Plant Diseases caused by BLOs

 Primary symptoms are discoloration of
 phloem tissue.
 Associated with newly described bacteria:
    within the clade Proteobacteria
    alpha or gamma subdivisions
    fastidious or unculturable
 Transmission is by sap-feeding insects.
Conclusions
 ZC continues to be a challenging disease of potatoes

 The cause, source, spread and subsequent control of
 this disease remains elusive

 It appears to be spreading, not only in the US, but in
 Mexico, Central America and possibly other areas

 It is a major cause for rejection of potatoes for
 processing into chips and tablestock because of the
 impact on quality
The exact cause of the disease remains
unknown
Work is continuing to identify the exact cause
of ZC
It is not caused by a Phytoplasma
DNA cloning and sequencing matches
Proteobacterium
However, we can not rule out a new virus

				
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posted:6/28/2011
language:English
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