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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)