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Common scab what do we know?
Tonya Wiechel DPI Victoria
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Acknowledgements

• Nigel Crump Soilborne Disease Team
• Kathy Ophel Keller and SARDI Team
• Tony Slater Potato Breeding Team
• Rod Lay McCain Ballarat
• Tine Thach 2007
• Michelle McCann 2004
• Gerardine Norden 2004
• Martin Sebire 2005
• Dannielle Danastasio 2006

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Life cycle of common scab disease
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Common scab symptoms

• Superficial
• Raised
• Deep pitted
• Netted

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Spore morphology
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Most isolates have spiral spore chains but this
is not related to symptom type
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Diagnostic test for pathogenic Streptomyces

• PCR (thaxtomin A gene)
• Gel electrophoresis

Txt A
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Most isolates produce thaxtomin A and this is not
dependent on spore chain type
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Infection of potato plants with isolates
2. Vermiculite
1. Goyer Loria broth
3. Mixing vermiculite and soil
4a. Planting a potato tuber
4b. Planting TC plantlet
5. Ready for green house
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S378 Raised TxtA -ve Flexous spore chain
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S381 Raised TxtA ve Spiral spore chain
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S384 Netted TxtA ve Spiral spore chain
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S385 Deep pitted txtA ve Spiral spore chain
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What level of pathogen causes disease?

• Glasshouse trials with artificially infested soil
• Glasshouse trials with naturally infested soils
• To determine inoculum threshold for disease
• To determine if DNA detection threshold is in the
  appropriate range

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Artificially infested mix
40 infested
Uninoculated
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Artificially infested mix
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Inoculum threshold of naturally infested soils

• Naturally infested soils collected from Ballarat,
  Victoria.
• Soil samples DNA tested by SARDI and used in this
  project.

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Effect of soil inoculum on disease
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003H
009L
006M
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Common scabdisease management
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Soil factors that may influence common scab
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Soil factors that may influence common scab

• 2004/2005 116 sites
• SA 29
• Tas 30
• Vic 57
• 2005/2006 117 sites
• SA 25
• Tas 30
• Vic 62

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Effect of Calcium on Common scab
Hot lime 5 t/ha
Hot lime 1 t/ha
Untreated
Perlka 1 t/ha
Gypsum 4 t/ha
Ag lime 15 t/ha
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CS incidence similar for all treatments Severity
gt with Hotlime 5t/ha Aglime Increased soil Ca
4000 ppm
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Common scab amendment 05/06 Simcoe
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Blue treatments significantly less than untreated
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Blue treatments significantly less than untreated
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Marketable and total yield
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Summary

• Soil factors have been identified that may be
  used to develop soil nutrition programs to reduce
  disease
• Different forms of calcium have different effects
  on common scab symptoms
• Field trials have found a number of organic
  amendments that reduce common scab disease

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Current future research

• Nutrient combinations and ratios on in vitro
  growth of Streptomyces (spore production
  biomass)
• Manipulate nutrients of interest in naturally
  infested soils with varying pathogen levels to
  reduce disease
• Decision support research to interpret DNA tests

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