Download - Citrus Canker 04-16-08
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CitrusCitrus
CankerCanker------------------------------------------------------------Biology andBiology and
EpidemiologyEpidemiology
Tim SchubertTim Schubert
Florida Department ofFlorida Department ofAgriculture & ConsumerAgriculture & Consumer
ServicesServicesDivision of Plant IndustryDivision of Plant Industry
Canker on Valencia orange
Canker on grapefruit
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Characteristics of the Citrus Canker Pathogen
Xanthomonas axonopodispv. citri
Characteristics of the Citrus Canker PathogenCharacteristics of the Citrus Canker Pathogen
Xanthomonas axonopodispv. citri
Size and shape - 1 by 3 microns, elliptical, covered with
slime, single polar flagellum. Reproduction - divide every 20-30 minutes. In 6 to 8 hours,
population can reach 1 million cells
Favorable environmental conditions = wet and warm.
Environmental niche - plant pathogen, not a good epiphyte orsaprophyte. Specifically pathogenic to citrus.
Infects citrus tissue in expansion phase of growth
Survival in nature - when it dries, it dies. Inoculum source - must emerge from existing lesions under
favorable conditions
Vectors - none
Size and shape - 1 by 3 microns, elliptical, covered with
slime, single polar flagellum. Reproduction - divide every 20-30 minutes. In 6 to 8 hours,
population can reach 1 million cells
Favorable environmental conditions = wet and warm.
Environmental niche - plant pathogen, not a good epiphyte orsaprophyte. Specifically pathogenic to citrus.
Infects citrus tissue in expansion phase of growth
Survival in nature - when it dries, it dies. Inoculum source - must emerge from existing lesions under
favorable conditions
Vectors - none
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How Xac causes canker
HowHow XacXac causes cankercauses canker
Bacteria must exit existing lesions under wet conditions Bacteria are wind-blown in water droplets to new location
OR
Bacteria are carried to a new location on plants, people orequipment Bacteria must impact susceptible citrus tissue with enough
force to penetrate stomatal aperture OR
Bacteria must enter into wounds in citrus tissue Bacteria induce surrounding cells to swell up and divide
abnormally Enzymes begin to degrade tissues, kill cells
Plant cell contents leak out to nourish bacteria
Bacteria must exit existing lesions under wet conditions Bacteria are wind-blown in water droplets to new location
OR
Bacteria are carried to a new location on plants, people orequipment Bacteria must impact susceptible citrus tissue with enough
force to penetrate stomatal aperture OR
Bacteria must enter into wounds in citrus tissue Bacteria induce surrounding cells to swell up and divideabnormally
Enzymes begin to degrade tissues, kill cells
Plant cell contents leak out to nourish bacteria
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How Citrus Canker Inoculum Gets DispersedHow Citrus Canker Inoculum Gets DispersedHow Citrus Canker Inoculum Gets Dispersed
Wind blown rain - Bacteria are blown from anexisting wet lesion to susceptible citrus in a vulnerable stageof growth with enough force to enter the stomates or getintroduced into a wound
Human activity People who work in and around citrus pick up inoculum on
their hands, clothes or tools, then unknowingly inoculatesusceptible citrus in another location
People move infected or exposed citrus from one location toanother
Wind blown rain - Bacteria are blown from anexisting wet lesion to susceptible citrus in a vulnerable stageof growth with enough force to enter the stomates or getintroduced into a wound
Human activity People who work in and around citrus pick up inoculum on
their hands, clothes or tools, then unknowingly inoculate
susceptible citrus in another location People move infected or exposed citrus from one location to
another
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Bacteria enter stomates and wounds
to start infection
Bacteria enter stomates and wounds
to start infectionwound
stomate
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The Canker SyndromeThe Canker Syndrome
Citrus canker diseaseaffects all above-ground tissues ofmost commercial
citrus cultivars Causal agent is a
bacterial pathogen
(Xanthomonasaxonopodispv. citri)
Grapefruit
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Anassortmentof cankerlesions on
fruit
Anassortmentof cankerlesions on
fruit
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Citrus canker beginningto defoliate and causetwig dieback on a youngcitrus tree in Argentina
Twig dieback from
stem infections on apummelo inHomestead, FL
Ad f h i l f i 1992
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Leaf miner damage (above)
Leaf miner larva in mine(upper right)
Adult moth of the citrus
leaf miner (right)
Advent of the citrus leaf miner - 1992Advent of the citrus leaf miner - 1992
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The Role of Citrus Leaf Miner in
Epidemiology of Citrus CankerPhyllocnistis citrella
The Role of Citrus Leaf Miner in
Epidemiology of Citrus CankerPhyllocnistis citrella
Leaf miner prefers young flush, same as CC Leaf miner larvae tunnel under leaf cuticle Feeding causes large amounts of wounded tissue
Canker inoculum easily washes into wounds Wounding increases the number of infectioncourts, infection is facilitated
More inoculum is produced from more lesions No stage of the insect life cycle serves as a
vectorNote: Natural resistance is greatly diminished in the presence
of leaf miner wounds
Leaf miner prefers young flush, same as CC Leaf miner larvae tunnel under leaf cuticle Feeding causes large amounts of wounded tissue
Canker inoculum easily washes into wounds Wounding increases the number of infectioncourts, infection is facilitated
More inoculum is produced from more lesions No stage of the insect life cycle serves as a
vectorNote: Natural resistance is greatly diminished in the presence
of leaf miner wounds
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Leaf miner damage
w/canker - front of leaf
Leaf miner damagew/canker - back of leaf
Close up view ofconfluent cankerlesions in leaf miner
wounds
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Spatiotemporal
Distribution ofCitrus Canker in
Urban MiamiCorrelation withStorm Frontal
Boundaries
Spatiotemporal
Distribution ofCitrus Canker inUrban Miami
Correlation withStorm Frontal
Boundaries On leading edge
of front, winds
normally blow tothe northeast
Behind front, to
the southwest
1995
1996
1997
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Effect of Removal of Canker
Infected Trees Over Time When exposed trees are
removed, you are actuallyremoving subclinical infections(undetected diseased trees) &trees that will become infected
over time. 125 exposed tree radius
removal only slows theacceleration: ~ 20% of newdiseased trees are removed.
To be effective, we need toremove enough infected &exposed trees to cause a netdecrease in incidence.
TimeTimeTime
No.
Infected
Trees
No.
Infected
Trees
No.
InfectedTrees
No ControlNo Control
125 ft Exposed Removal125 ft Exposed Removal
Theoretical RemovalTheoretical Removal
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Prerequisites and data collection for the
South Florida canker epidemiological study
Prerequisites and data collection for theSouth Florida canker epidemiological study
Little or no disease should be detectable in theimmediate disease frontier area at start
All citrus host trees in the area should beidentified by initial survey and their preciselocation mapped
When diseased trees are detected during periodicsurveys, a date of infection is calculated
In subsequent surveys, previously identifiedinfected trees are considered focal trees for thenext generation of infected trees
Nearest neighbor concept is used to identifysource of inoculum for next generation of infectedtrees
Earliest data gives the best estimate of diseasespread potential
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% Capture D1 D2 D3 B1A B2A Cumulative
90 700 500 1150 950 650 700
95 1200 700 1450 1350 1100 1100
99 1800 1400 1950 2950 1550 1950
0
10
20
30
40
50
60
70
80
90
100
5 0
2 5 0 4 5 0 6 5 0 8 5 0
1 0 5 0 1 2 5 0
1 4 5 0 1 6 5 0 1
8 5 0 2 0 5 0 2 2 5 0 2
4 5 0 2 6 5 0 2
8 5 0 3 0 5 0 3 2 5 0 3
4 5 0 3 6 5 0 3
8 5 0
Distance(Feet)
PercentCapture(%)
MiamiSite1
MiamiSite2
MiamiSite3
BrowardB1A
BrowardB1B
COMPOSITE
30
40
50
60
70
80
90
100
50
250 4 50 6 50 850
1050 1 250 1 450 1650 1 850 2 050 2250 2 450 2 650 2850 3050 3 250 3450 3 650 3 850Distance(Feet)
PercentCapture(%)
MiamiSite1
MiamiSite2
MiamiSite3
BrowardB1A
BrowardB1B
COMPOSITE
Miami Citrus Canker, 30-day Temporal Window
-- Cumulative Percent Capture
0
10
20
30
40
50
60
70
80
90
100
50 25
0450
650
850
1050
1250
1450
1650
1850
2050
2250
2450
2650
2850
3050
3250
3450
3650
3850
Distance (Feet)
PercentCapture(%)
Miami Site 1
Miami Site 2
Miami Site 3
Broward B1A
Broward B1BCOMPOSITE
Gottwald, et al., 2002
05 04 03 02 01 00 99 98 97 96 9505 04 03 02 01 00 99 98 97 96 95
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The Spread of CitrusCanker in SE Florida
1995-2005
The Spread of CitrusCanker in SE Florida
1995-2005
05 04 03 02 01 00 99 98 97 96 9505 04 03 02 01 00 99 98 97 96 95
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2004-2005Hurricanes andTropical Storms
in Relation toCommercialCitrus
ProductionAreas
2004-2005Hurricanes andTropical Storms
in Relation toCommercial
Citrus
ProductionAreas
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Estimated total annual costs of letting
Estimated total annual costs of letting
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$93.4 million for additional grower outlays tocontain canker
$78.2 million in lost on-tree revenue to growers
$170.4 million lost in FOB value of fresh citrus
export shipments-------------------------------------
Other considerations:
No consideration of economic impact of industry shrinkage
Overall economic impact of citrus industry to Florida economyis over $9 billion
Citrus industry directly or indirectly provides 126,000 full timejobs
Estimated total annual costs of lettingcanker become endemic in Florida
(Florida Citrus Mutual)
Estimated total annual costs of lettingcanker become endemic in Florida
(Florida Citrus Mutual)