best strategies for prevention of crown gallcetehama.ucanr.edu/files/23204.pdf · crown gall...
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Best Strategies for Prevention of Crown Gall
Richard Buchner – UCCE Tehama
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Crown Gall Disease of Walnuts
Causative agent:Agrobacterium tumefaciens
> ubiquitous soil-borne bacterium
> long term persistence
> natural genetic engineer
> wide host range; (”all” dicots)
> economic impact on walnut
> essentially “girdles” trees
> Paradox root stock highly susceptible
> ability to exist systemically
> very damaging to young trees
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How the disease works
• A. tumefaciens can transfer tumor producing genes into plant nuclei in the form of tumor-inducing plasmids. These plasmids carry the tumor-inducing genes and can transfer them to host cells. Genes are encoded to produce Auxin and Cytokinin which cause gall formation.
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Crown Gall is a very challenging disease to work on. As a result, there is not a great deal of good replicated CG research on walnut.
• Different pathogen strains• Genetic differences in Paradox• Variable inoculum levels• Variable soil conditions
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Options for preventing Crown Gall
• Plant non-infected trees– Discard any trees with visable galls– Bare root tree storage – Lynn Epstine UCD– Plant non-infected seeds – Kluepfel UCD
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Options for preventing Crown Gall
• Methyl Bromide is effective on A.tumefaciens, however, A.tumefaciens can re-colonize in soil to higher levels in fumigated soil (Kluepfel UCD).
• Chance for reinfection with trees/seed.
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Options for preventing Crown Gall
• Choice of root stock• Most seedling Paradox highly sensitive• Black is more tolerant but not totally resistant• Several Juglans species exhibit resistance to
crown gall• GMO root stock – clonal propagation
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Options for preventing Crown Gall
• Avoid tree damage• Wounds that expose cambium• Crown injury from cultivation
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Options for preventing Crown Gall
• Avoid spreading with infected tools• Contaminated soil• Equipment or plant material
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Options for preventing Crown Gall
• Use care with suckers• Nitrogen –• Flaming –
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Options for preventing Crown Gall
• Control gophers and rodents• Weed control in strips
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Options for preventing Crown Gall
• Plant trees as high as possible• May lessen exposure• Usually make treatment easier
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If all else fails, expose galls and treat
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Pneumatic Excavation
• 90 psi at 150 cfm, ¾ inch diameter hose with a Mach 2 nozzle.
• 90 psi at 330 cfm, 1 ½ inch diameter hose with a Mach 2 nozzle.
http://walnutresearch.ucdavis.edu
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Hydraulic Excavation
• One inch diameter forestry hose with KK ThunderFog nozzle (variable flow rate) or TFT Midmatic (automatic pressure regulating) nozzle.
• One and one-half inch diameter “attack line” hose with nozzles as above.
• Pressure washer, might be convenient but slow. Hold nozzle a foot or more from roots to avoid damage.
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Treatments
• Tissue around the gall is critical to treat• In our tests, chemical treatments alone were not
effective (http://walnutresearch.ucdavis.edu)• Clean surgery is effective• Killing surrounding bark with heat is effective• Surgery plus heat is the preferred method• Get them when they’re small• Leave exposed for any “escapes”
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For more information, go to…
http://walnut.research.ucdavis.eduScroll down to root, crown and graft union diseases
and click on crown gallDan Kluepfel – current researchLynn Epstine – biology and controlBill Olson – economic effectRichard Buchner – treatmentsJanine Hasey – pneumatic soil excavation