Erwinia amylovora fire blight of apple and pear

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Erwinia amylovora fire blight of apple and pear
The Fisher-Smith Debate (1890s) Smith
established that bacteria can cause plant
diseases
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Erwinia amylovora fire blight of apple and pear
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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

• Control
• Resistant cultivars (Red Delicious) and
  rootstocks
• Limit nitrogen
• Prune all infections (burn)
• Chemical controls (Disease forecasting)
• Copper not very effective
• Oxytetracycline
• Streptomycin (resistance)
• Biological controls
• Commercially available BlightBan (P. fluorescens
  A506) mix with antibiotics

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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 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? Originated in China, with
citrus First found in US 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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Important Concepts in Phytobacteriology
Bacterial pathogens gain access to plants through
wounds or natural openings. They can be
transmitted by insects.
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Gram Gram -
Y
First question is the species Gram positive or
Gram negative?
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Streptomyces industrial uses
Antibiotic production streptomycin
Streptomycin is used to control fire
blight Large genomes, which encode for many
secondary metabolites, are being mined for new
antibiotics
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Streptomyces - common scab
Gram-positive, filamentous bacteria Common in
soils worldwide Causes pitted lesions on root
and tuber crops Only causes symptoms on growing
plant tissue Symptoms due to a toxin that
inhibits cellulose synthesis Controlled by
proper irrigation and manipulating soil pH
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Streptomyces - common scab
fas genes produce plant hormone
cytokinin Causes root cell swelling and in lab
can cause galls to form
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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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Clavibacter michiganensis subsp. sepedonicus
bacterial ring rot
Symptoms plants wilt, vascular ring of potato
tuber rots, only infects potato Sign bacterial
ooze from tubers and stems Gram positive
bacteria that only survive in association with
potato debris or slime. Can survive in dried
slime for years Major problem in potato
production because can spread without symptoms
for several years, then disease is triggered by
environmental conditions.
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Bacterial ring rot and potato spindle tuber used
to be common diseases
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Ring Rot
Spindle Tuber
Percent lots rejected - summer field readings
Total
5
0
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
1941-1965
1966-1970
1976-1985
Year
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Estimate of value of reduction in bacterial ring
rot and spindle tuber
1941-1965 2005 1 loss 5 loss levels dollars
in x of crop in x of crop Bacterial Ring
Rot 12 2,400,000,000 2,900,000 14,400,000 Spi
ndle Tuber 5 2,400,000,000 1,200,000 6,000,0
00 Total 4,100,000 20,400,000
Estimate of acreage fees and inspection fees in
US 5 million/year Can this disease be
eradicated?
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Where did ring rot come from?

• First found in North America in 1930s
• Spread quickly throughout US
• In 10 yrs, growers went from never having seen
  BRR to having up to 20 of lots infected with
  this pathogen

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Ring Rot control in the 1940s

• 0 tolerance for BRR instituted in all seed
  potato producing states in 1940s
• Yearly survey of state seed potato certification
  standards initiated to help growers and
  certifiers keep track of variations in regulations

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Ring Rot control in the 1940s

• Strict response due to commercial growers that
  wrote to recommend and urge the setting up of a
  very rigid federal potato seed certification
  law.

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Ring Rot and WWII

• Height of first BRR outbreak was in early 1940s
• Many inspectors drafted, so difficult to run
  certification programs

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Ring Rot and WWII

• Many potatoes were shipped overseas to feed
  troops
• Prices in US were government-regulated resulting
  in potato black market and disruption of seed
  supply

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Ring Rot and WWII

• War-certified tags developed in 1942
• In 1943, over 1/3 of certified seed was tagged
  with orange war-certified tags

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Ring Rot Control

• Most critical control information discovered
  prior to 1940
• Sanitation
• Clean seed

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Clavibacter michiganensis subsp. michiganensis
bacterial canker
Causes tomato stems to wilt and rot Survives well
on stems and leaves Major difference between
subspecies is that Cms has many copies of an
insertion element lacking from Cmm
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Clavibacter michiganensis subsp. sepedonicus
bacterial ring rot
Gram positive bacterial pathogen Symptoms
plants wilt, vascular ring of potato tuber rots,
only infects potato Sign bacterial ooze from
tubers and stems Gram positive bacteria that
only survive in association with potato debris or
slime. Can survive in dried slime for years and
spread in latently infected potatoes. Spread
into US in 1930s, still causing losses today.
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Plant Pathogenic Mollicutes Phytoplasma

• Disease
• Phytoplasma are present in sap of phloem sieve
  tubes
• Growth regulator production by plant disrupted
  witches brooming
• Phytoplasmas overwinter in infected weed hosts
  and perennial ornamentals
• Black-eyed Susans
• Field daisy
• Thistle
• Wild carrot
• dandelion

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Phytoplasma Aster Yellows
Floral parts are replaced by vegetative structures
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Phytoplasma Aster Yellows on Strawberry
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Phytoplasma Aster Yellows

• Example of control by application of insecticides
  to control vector
• Timing of insecticide is critical

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Signs of Bacterial Infection
Streaming
Threads
Oozing
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• How bacteria damage host cells
• 1. Toxins
• Degradative enzymes
• Secreting (translocating) DNA or proteins into
  plant cells
• Extracellular polysaccharides (EPS)
• Plant hormones

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• How bacterial diseases are controlled
• 1. Sanitation equipment, storages, and workers
• Exclusion use clean seed and healthy plants,
  quarantines
• Antibiotics or copper sprays
• Biocontrol
• Insecticides