Applying crown gall research-based knowledge to orchard management E. Fichtner, UCCE Tulare County
Paradox: Juglans hindsii x Juglans regia Crown Gall Common in walnut Paradox rootstock susceptible Less common on black walnut rootstock
Crown gall and root gall Photo: Epstein et al. Cal Ag
Hairy Root Agrobacterium rhizogenes Photo: E. Fichtner, Fresno Co.
Crown Gall Hairy Root Photo: E. Fichtner, Tulare Co.
Crown Gall Agrobacterium tumefaciens Gram negative bacterium Soilborne pathogen -fungicides ineffective -bacteriacides limited
Agrobacterium tumefaciens Broad host range: dicots only Motile- flagella, chemotaxis ubiquitous soil bacterium biotrophic plant pathogen (keeps the host alive) Long-term soil survival
Ubiquitous but chromosome plasmid Not all isolates are pathogenic
Tumor inducing plasmid Virulence T DNA Plant Recognition Etc. pti flagella Chromosome Plant Recognition Chemotaxis Attachment
plasmid + plasmid
The induction of a grown gall is a multi-step process Wound or Natural Opening Transformation of Plant Cells Cell Proliferation
Ti Plasmid Well-categorized/sequenced Can be manipulated Used in genetic engineering
Scion conventional trans Rootstock
Crown Gall Tree Size Irrigation issues Yield Predisposition to other diseases/pests
Tree Size
Infected Trees overwatered, earlier senescence
For every quarter of trunk circumference galled, there was a 12% decrease in cumulative nut yield over the first 4 years of production. (Epstein, et al. 2008 California Agriculture) Crown Gall Yield Tree size Yield
2016: Kings County (Yaghmour, Facundo, Fichtner) Crown Gall No Crown Gall 0 2 4 6 8 10 12 Tree Diameter (In) 26% of the variability of trunk diameter attributed to crown gall
WTB
Crown Gall Thousand cankers disease Yes No Total Yes 41 27 No 1 98 Total 42 (25.1%) 125 (74.9%) 68 (40.7%) 99 (59.3%) 167 (Yaghmour, Facundo, Fichtner)
# larvae/tree 2010: TLJB/Crown Gall Survey t 0.06 Mapped out crown gall incidence. Randomly selected 8 gall-infected trees. Selected neighboring paired asymptomatic tree. Trenched around trees; counted grubs. Labor intensive; high variability. (Fichtner, 2010)
Management Rootstock Selection Q) Are seedlings more susceptible than clones?
Crown gall in rootstock plot Seedling Paradox only Clonal almond rootstock (R. Duncan) RX1-low/moderate resistance?
4 rows Tulare County Walnut Rootstock Block Planted in 2016 SCRI Rootstock Block
January 2019 Walnut Rootstock Block
Rx1 has J. microcarpa parent
Soilborne History of site monocots/dicots? Prior disease? Sources of inoculum
Kern County, clonal rootstock
2019: Kern Co. 2016: Tulare Co. Field grafted late; clonal rootstock
Possible sources of inoculum: 1) Dirty grafting knife 1) Surface-infested budwood 1) Endophyticbudwood
Infestation of budwood
Infestation of budwood time
Rootstock mother tree J. hindsii; pollinated by J. regia
Rootstock mother tree J. hindsii; pollinated by J. regia
Experimentally Inoculated seed Crown gall on 94% Paradox seedlings Experimentally Infested soil Crown gall on 93% Paradox seedlings Yakabe, et al. Plant Disease. 2012
A. tumefaciens can move systemically in walnut Yakabe, et al. Plant Disease. 2012
Endophytic populations may be asymptomatic May be inadvertently transmitted in nurserystock Symptoms may appear much later at wound sites. In this study: 17% of seedlings inoculated as seed developed secondary galls at wound sites. Roots are an inoculum reservoir Yakabe, et al. Plant Disease. 2012
Disease Transmission with sequential cuts Paradox Yakabe, L.E. et al, 2012
Tool Sanitization Sodium hypochlorite (bleach) Pros Cons Cheap Corrodes tools Eliminates At at 0.5 ppm Phytotoxic Efficacy reduced w/ solids Percent reduction in At populations Total Solids (g/ml) 0 93 0.7 29 1.5 11 2.0 4 3.0 2 Sodium hypochlorite (0.02 ppm) Yakabe, L.E. et al, 2012
Tool Sanitization Cationic surfactants (quarternary ammonium compounds): BC, CTAB, Physan 20 Pros Cons non-corrosive cost Efficacy maintained with particulates Non-phytotoxic Yakabe, L.E. et al, 2012
Percent reduction of Agrobacterium tumefaciens Bleach Physan Yakabe, L.E. et al, 2012
Tree Removal vs. Gall Removal 1 st leaf trees: Remove and replant 2 nd leaf trees: Remove and replant trees with large galls ( ¼ diameter) Treat those with small galls 3 rd -7 th leaf trees: Treat unless completely girdled 7 th leaf and older: Don t treat. Olson and Buchner, 2001
Biological Control Pre-plant/protectant Agrobacterium radiobacter Commercial names: Galltrol A, Norbac 84C, Nogall, or Diegall Efficacy varies based on isolate and environment Post-plant treatment ie. Gallex Phenols Applied to galls or as a disinfectant after gall excision
Pre-Plant Treatment Fumigate with Telone C-35 or Telone C-35 followed by chloropicrin in crown gall infested sites. Consider the Biological Vacuum
Consider the Biological Vacuum Unfumigated Fumigated
Management from nursery to field Consider inoculum: soil, seed, systemic, tools Consider rootstocks: Paradox susceptible (RX1 option) Treatment vs. Replant: Tree age and degree of symptoms