Antimicrobial Therapies for HLB and Canker

Stephanie Slinski, CRDF Antimicrobial Project Manager

Citrus Research and Development Foundation, Inc.

700 Experiment Station Road • Lake Alfred • FL • 33850 863-956-8817 citrusrdf.org

Florida Citrus Growers’ Institute

April 7, 2015

Materials Available Now for Canker and HLB

Canker

•Copper

•FireWall™ (grapefruit only) Follow label

HLB

•No effective treatment has been identified How to identify effective treatments?

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HLB Disease TetrahedronHost

Pathogen Environment

Vector• Virulence of Pathogen• Amount of bacteria in the

host plant

• Amount of Vector• Ability of vector to acquire and spread

the bacteria • Infection cycles (with flushing cycles)

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e.g. Moisture and temperature

HLB Disease TetrahedronHost

Pathogen Environment

Vector

• Level of Susceptibility• Genetic Uniformity• Age of Host• Human Factors

o Site selectiono Propagation materialo Cultural practices

• Fertilization• Irrigation

Resistant Host

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HLB Disease TetrahedronHost

Pathogen Environment

VectorAntimicrobial Therapies

• Maintain health of existing trees

• Protect new plantings

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Vascular Plant Pathogens

OrganismLocation in

PlantControl Measures

Lethal Yellowing of Palm PhloemRemove Inoculum, Vector Control, Resistant Host, Antibiotics for specimen plants*

Xylella fastidiosa (Pierce’s disease, citrus variegated chlorosis disease, etc.)

Xylem Remove Inoculum, Vector Control, Resistant Host

Serratia maecescens (cucurbit yellow vine disease) Phloem Remove Inoculum, Vector Control, Resistant Host

Ralstonia solanacearum (Bacterial wilt of multiple crops) Xylem Remove Inoculum, Resistant Host, Rotation

Elm Yellows PhloemRemove Inoculum, Vector Control, Resistant Host, Antibiotics for specimen plants*

Pantoea stewartii (Stewart’s wilt of corn) Xylem Remove Inoculum, Vector Control, Resistant Host

*Only slows disease progression

Prevention is the only control method used for vascular plant pathogens4/27/2015 www.citrusrdf.org 6

Vascular Plant Pathogens

OrganismLocation in

PlantControl Measures

Lethal Yellowing of Palm PhloemRemove Inoculum, Vector Control, Resistant Host, Antibiotics for specimen plants*

Xylella fastidiosa (Pierce’s disease, citrus variegated chlorosis disease, etc.)

Xylem Remove Inoculum, Vector Control, Resistant Host

Serratia maecescens (cucurbit yellow vine disease) Phloem Remove Inoculum, Vector Control, Resistant Host

Ralstonia solanacearum (Bacterial wilt of multiple crops) Xylem Remove Inoculum, Resistant Host, Rotation

Elm Yellows PhloemRemove Inoculum, Vector Control, Resistant Host, Antibiotics for specimen plants*

Pantoea stewartii (Stewart’s wilt of corn) Xylem Remove Inoculum, Vector Control, Resistant Host

*Only slows disease progression

Antibiotics are used for prevention of treatment of landscape or specimen plants4/27/2015 www.citrusrdf.org 7

Major Hurdles to Finding an Effective Therapy

•Delivery Foliar delivery for a vascular pathogen?

o Trunk injection

o Penetrants, new chemistries

•Pesticide Registration Most effective therapies have a long regulatory pathway

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Goals of CLas Chemical Therapy

•Stabilize/reverse decline of chronically infected trees

•Reduce bacterial titer

•Allow for recovery of fruit production while replanting

•Treat new infections early

•Sequential development of better tools

Not viewed as permanent solution

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CRDF Antimicrobial Therapy Efforts

• Testing materials from industry and researchers Known agricultural bactericides

o Streptomycino Oxytetracycline

Re-purposed bactericides – human and vet med Biopesticides – registered and new Plant Essential Oils EPA 25(b) Exempt List and GRAS-like (FDA) Copper and other metals Libraries of active ingredients - industry

•Discovery – new actives through funded research

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Evaluation Criteria

• Bactericidal activity

• Dose response

• Formulation for phloem movement

• Application methods – foliar, trunk, roots

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Stepwise Assay System

Field Use

Liberibacter crescens (laboratory) assay-tests bactericidal activity and dose response

Flush or detached leaf (laboratory) assay-tests activity against CLas, local movement, dose response, phytotoxicity

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Secondary Evaluation Criteria

• Manufacturing and Scale-Up

• Intellectual Property

• Regulatory Feasibility

• Cost to Grower

• Availability/Time-to-Market

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Antimicrobial Therapy Prioritization

• Materials are prioritized based on evaluation criteriaand ranked within antimicrobial class using an “Antimicrobial Therapy Candidate Matrix”

Categories:o Biopesticideo GRAS/ “Minimal-Risk”o Conventional Antibiotico Agricultural Antibiotico New Molecular Entity

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Short-Term Solution

Medium-Term Solution

Next Generation Solution

Antimicrobial Therapy Candidate Matrix

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Stepwise Assay System

Field Use

Liberibacter crescens (laboratory) assay-tests bactericidal activity and dose response

Flush or detached leaf (laboratory) assay-tests activity against CLas, local movement, dose response, phytotoxicity

Whole plant (greenhouse) assay-tests phloem entry and mobility, activity against CLas, dose response and phytotoxicity

Field trials-tests activity, dose response, phloem entry and mobility, phytotoxicity, application methods, residues, fruit drop and quality

Increase in biological relevance

Decrease in throughput

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Short-Term Solutions

•GRAS/Biopesticides ThymeGuard

o Available now, labeled for citrus

o No efficacy data, soon to be tested in field trials

Other Essential Oil Formulation

o Field trial with three year old trees Preventative

Curative

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Short-Term Solutions

•GRAS/Biopesticides These categories are prioritized based on time to market May be most effective in combination with other

treatmentso Thermal therapyo Antibiotic treatment (maintenance)

We continue to test similar materials in our assayso Foliar uptakeo Bactericidal/suppressiveo Alternative delivery methods

Working with several companies with new materials Delivery is the highest hurdle

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Medium-Term Solutions

Funded Field Trials (CRDF, NIFA, MAC)

•Agricultural antibiotics

•Zinc materials Also for canker control/treatment

•Agricultural chemicals Label for citrus

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Next Generation Materials

Five or more years to complete studies for registration

•Nanosilver

•Tetracycline derivatives

•Repurposed bactericides (human or vet med) Possibly medium-term if some studies have been

conducted

Conclusions

•Few treatments for HLB and canker are available presently

•No history of curing vascular plant pathogens

•Delivery is the main hurdle

•CRDF has developed a step-wise assay system to evaluate potential material

•We are working to find materials that facilitate movement into the phloem as well as new delivery methods

Thank you!

CRDF is proud to provide support to the Florida citrus industry

Citrus Research and Development Foundation, Inc.