Pectobacterium and Dickeya soft rot, blackleg and wilt

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Pectobacterium and Dickeya soft rot, blackleg
and wilt
Most are broad host range pathogens Most problems
caused on vegetables and ornamentals
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Pectobacterium and Dickeya soft rot, blackleg
and wilt
Major virulence factor plant cell wall
degrading enzymes -pectate lyases -polygalacturona
ses -cellulases -xylanases -proteinases
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Pectobacterium and Dickeya soft rot, blackleg
and wilt
Enzymes digest plant cell walls. Plant cells
have high turgor pressure, so pop like water
balloons when cell wall is breached. Soft rot
bacteria eat plant cell wall components
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Pectobacterium and Dickeya soft rot, blackleg
and wilt
Soft rot bacteria act as a group Quorum sensing
via acyl-homoserine lactones controls enzyme
production, so plant cell wall degrading enzymes
are only produced when the bacteria are present
at high levels First example of quorum sensing
in bacterial pathogenesis
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Pectobacterium and Dickeya soft rot, blackleg
and wilt
Why are not all plant digested by soft rot
bacteria? Plants can defend themselves against
enzyme attacks Generally only get soft rot or
wilt disease from these pathogens on stressed
plants
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Ralstonia soalacearum bacterial wilt
Sudden wilt, no yellowing
Sign of bacterial infection bacterial
streaming Ralstonia has characteristic streaming
compared to soft rot pathogens. Useful for
in-field diagnosis.
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Bacterial Anatomy Cell wall and membranes
Cytoplasm and periplasm Genome
Chromosome(s) and plasmids (DNA)
Extracellular polysaccharide Flagella, pili,
and fimbriae
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Ralstonia soalacearum bacterial wilt
Ralstonia is frequently imported into the US on
ornamental plants. Often the plants are
symptomless latent infections
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Pectobacterium and Dickeya industrial uses
Enzymes for bioenergy
Asparaginase enzyme to treat cancer
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Pectobacterium and Dickeya soft rot, blackleg
and wilt Ralstonia solanacearum bacterial wilt
Pathogen gram-negative rod bacterium Symptoms
caused mainly by enzymes that degrade plant
cell walls. Quorum sensing regulates enzyme
production. Present in soil and water Broad
host range pathogens -Pectobacterium and Dickeya
mainly cause disease on stressed
plants -Ralstonia is more aggressive Control -san
itation, clean seed (avoidance) Industrial uses
in bioenergy and cancer treatment
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Important Concepts in Phytobacteriology
Bacterial pathogens gain access to plants through
wounds or natural openings. They do not make
their own openings into plants Bacterial
pathogens can acquire new virulence genes via
horizontal transfer Bacterial pathogens can
manipulate plant cells by injecting DNA or
proteins into plant cells or with
toxins Bacterial pathogens do not rely on just
one virulence gene. Pathogenesis is due to small
and overlapping contributions from many
genes Bacteria act as a group
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Erwinia amylovora fire blight of apple and pear
Dissemination Rain and insects
Shepherds crook
Blossom stage is key to control keep
populations on stigmas lt106 cells/blossom
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Erwinia amylovora fire blight of apple and pear
This pathogen has two T3SS, one is required for
growth in plants. The second may be required for
growth in insects.
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Erwinia amylovora fire blight of apple and pear
Disease sign bacterial ooze from fruit, stems,
and trunks
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Erwinia amylovora fire blight of apple and pear
Hopeful bulletin from the Washington State
Agricultural Experiment Station February, 1915
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Erwinia amylovora fire blight of apple and pear
The Fisher-Smith Debate Smith established that
bacteria can cause plant diseases
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Erwinia amylovora fire blight of apple and pear

• Control
• Resistant cultivars (Red Delicious) and
  rootstocks
• Limit nitrogen
• Prune all infections (burn)
• Chemical controls (Disease forcasting)
• Copper not very effective
• Oxytetracycline no resistance but only 50
  reduction.
• Streptomycin - antibiotic resistance.
• Biological controls
• Commercially available BlightBan (P. fluorescens
  A506) mix with antibiotics

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Erwinia amylovora fire blight of apple and pear
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Erwinia amylovora fire blight of apple and pear
Pathogen gram-negative rod bacterium Causes
necrotic blight of apple and pear trees. Spread
mainly by insects pollinating flowers Signs of
fire blight include oozing fruit, stems, and tree
trunks First plant disease to be shown to be
caused by bacterial pathogen (Fisher-Smith
Debate) Biocontrol and chemical control are
used. One of few examples where antibiotics are
used to control a plant disease.
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Important Concepts in Phytobacteriology
Bacterial pathogens gain access to plants through
wounds or natural openings. They do not make
their own openings into plants Bacterial
pathogens can acquire new virulence genes via
horizontal transfer Bacterial pathogens can
manipulate plant cells by injecting DNA or
proteins into plant cells or with
toxins Bacterial pathogens do not rely on just
one virulence gene. Pathogenesis is due to small
and overlapping contributions from many
genes Bacteria act as a group
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Xanthomonas axonopodis pv. citri citrus canker
Invasive disease? First found around 1912 -
declared eradicated in 1933 Found in 1986 -
declared eradicated in 1994 Found in 1995 now
widespread despite eradication efforts Symptoms
blister like lesions on stems, leaves, and
fruit. Fruit drops off of infected trees
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Xanthomonas axonopodis pv. citri citrus canker
Xanthomonas species can infect most types of
plants Inject proteins into plant cells with the
T3SS Proteins travel to plant nucleus, bind to
DNA, and turn on specific plant genes that make
the plant susceptible to infection
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Xanthomonas axonopodis pv. citri citrus canker
Extensive eradication efforts in Florida
Removal or cutting back of gt1.56 million
commercial trees and nearly 600,000 yard
trees Infected area continues to increase
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Xanthomonas axonopodis pv. citri citrus canker
Introduction of Asian leaf miner has made disease
situation worse since wounds from leaf miner
feeding serve as infection sites for bacteria
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Xanthomonas axonopodis pv. citri citrus canker
Controlled in the US and other citrus growing
countries by cutting and burning trees and
spraying copper.
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Xanthomonas industrial uses
Food grade xanthan gum can be widely used as
salt/acid resistant thickener, high efficient
suspension agent and emulsifier, high viscosity
filling agent in various food and beverage. It
can not only enhance the performance of
water-keeping and shape-keeping, but also improve
the freeze/thaw stability and mouth-feeling of
food and beverage product
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Xanthomonas axonopodis pv. citri citrus canker
Pathogen gram-negative rod Xanthomonas relies
on the T3SS for growth in plants Xac is spread
by wind, water, and insects Citrus canker is
controlled by removing trees and use of copper
sprays Xanthomonas infects most plants, but each
strain is specific to particular plant species or
variety
Black rot, cabbage
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Important Concepts in Phytobacteriology
Bacterial pathogens gain access to plants through
wounds or natural openings. They do not make
their own openings into plants Bacterial
pathogens can acquire new virulence genes via
horizontal transfer Bacterial pathogens can
manipulate plant cells by injecting DNA or
proteins into plant cells or with
toxins Bacterial pathogens do not rely on just
one virulence gene. Pathogenesis is due to small
and overlapping contributions from many
genes Bacteria act as a group
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Citrus Huanglongbing - citrus greening disease
Huanglongbing yellow shoot disease in
Chinese First described in India in the 1700s,
recently found in Florida Infected trees develop
yellow shoots and mottled leaves
Fruit is distorted and bitter. Not suitable for
juice.
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Citrus Huanglongbing - citrus greening disease
Transmitted by two citrus psyllid species. The
fourth and fifth instar nymphs can acquire the
pathogen which the emerging adult can transmit
persistently. Pathogen is probably the
Candidatus Liberibacter asiaticus bacteria. It is
limited to within citrus phloem sieve tubes and
has not yet been cultured.
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Citrus Huanglongbing - citrus greening disease
HLB is more serious than Xanthomonas citrus
canker Eradication efforts are on-going May
result in end of shipment of fresh citrus from
Florida in order to protect industries in Texas
and California.
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Important Concepts in Phytobacteriology
Bacterial pathogens gain access to plants through
wounds or natural openings. They do not make
their own openings into plants Bacterial
pathogens can acquire new virulence genes via
horizontal transfer Bacterial pathogens can
manipulate plant cells by injecting DNA or
proteins into plant cells or with
toxins Bacterial pathogens do not rely on just
one virulence gene. Pathogenesis is due to small
and overlapping contributions from many
genes Bacteria act as a group