Epidemiology of Spongospora root infection Tamilarasan Thangavel - - PowerPoint PPT Presentation

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Epidemiology of Spongospora root infection Tamilarasan Thangavel - - PowerPoint PPT Presentation

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2 nd International Powdery Scab Workshop | Pretoria, South Africa | July 29 August 1, 2014 Epidemiology of Spongospora root infection Tamilarasan Thangavel Robert Tegg Calum Wilson UTAS 2 nd International Powdery Scab Workshop | Pretoria,

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Epidemiology of Spongospora root infection

Tamilarasan Thangavel Robert Tegg Calum Wilson

2nd International Powdery Scab Workshop | Pretoria, South Africa | July 29 – August 1, 2014

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2nd International Powdery Scab Workshop | Pretoria, South Africa | July 29 – August 1, 2014

UTAS

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2nd International Powdery Scab Workshop | Pretoria, South Africa | July 29 – August 1, 2014

UTAS

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Merz (2008) quotes: “…. we still lack basic knowledge on the etiology and epidemiology of the disease.” This lack of knowledge has severely limited the capacity to develop effective disease mitigation strategies

2nd International Powdery Scab Workshop | Pretoria, South Africa | July 29 – August 1, 2014

Outline

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2nd International Powdery Scab Workshop | Pretoria, South Africa | July 29 – August 1, 2014

Outline

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  • Potato root infection by Spongospora subterranea f.sp.

subterranea is of considerable significance

  • Root infection is the primary source of inoculum build up in the soil

2nd International Powdery Scab Workshop | Pretoria, South Africa | July 29 – August 1, 2014

Outline

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2nd International Powdery Scab Workshop | Pretoria, South Africa | July 29 – August 1, 2014

Outline

  • Tasmanian soils have very high pathogen

inoculum levels (often 10-25,000 pg/g)

  • The major cultivar (Russet Burbank) grown

is relatively susceptible to root infection AND has a relatively weak root system

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2nd International Powdery Scab Workshop | Pretoria, South Africa | July 29 – August 1, 2014

Outline

  • Tasmanian soils have very high pathogen

inoculum levels (often 10-25,000 pg/g)

  • Tasmanian processors estimate yield losses
  • f 10-20% regularly occur
  • The major cultivar (Russet Burbank) grown

is relatively susceptible to root infection AND has a relatively weak root system

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2nd International Powdery Scab Workshop | Pretoria, South Africa | July 29 – August 1, 2014

Project aims

  • To better understand the dynamics of disease progression in

potato roots

  • To examine the influence of delayed inoculation and root

system maturity on disease progression

  • To examine the effect available chemical treatments and

seed health on suppression of disease progress

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2nd International Powdery Scab Workshop | Pretoria, South Africa | July 29 – August 1, 2014

Experiments

  • A series of glasshouse and field trials were established

assessing root infection dynamics

  • 4 x trials assessing the effect of delayed infection
  • 4 x trials assessing the effect of seed and soil treatments
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2nd International Powdery Scab Workshop | Pretoria, South Africa | July 29 – August 1, 2014

Delayed inoculation

  • Inoculum was added periodically during the plant growth cycle

(at emergence, 10, 20, 30, 40 & 50 days after emergence)

  • Plants were periodically harvested (every 15 days)
  • Disease/pathogen assessments
  • Zoosporangia score
  • Root gall score
  • Tuber disease score
  • Pathogen quantification (qPCR)
  • Plant growth assessments
  • Fresh weight
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1 10 100 1000 10000 100000 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 115 120 Log DNA content At emergence 10 DAE 20DAE 30 DAE 40 DAE 50 DAE

2nd International Powdery Scab Workshop | Pretoria, South Africa | July 29 – August 1, 2014

Delayed inoculation

1 10 100 1 000 10 000 100 000 1 000 000 10 000 000 15 30 45 60 75 90 105

Content of pathogen (Log (mean Spongospora DNA +1)) in roots

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2nd International Powdery Scab Workshop | Pretoria, South Africa | July 29 – August 1, 2014

Delayed inoculation

0.2 0.4 0.6 0.8 1 1.2 1.4 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 115

Root gall score

At emergence 10 DAE 20DAE 30 DAE 40 DAE 50 DAE 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 115

Zoosporangia score

Root gall and Zoosporangia scores

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2nd International Powdery Scab Workshop | Pretoria, South Africa | July 29 – August 1, 2014

Delayed inoculation

0.5 1 1.5 2 2.5 3 3.5 10 20 30 40 50 Tuber disease score (0-6) Inoculation date

Tuber disease scores at harvest

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2nd International Powdery Scab Workshop | Pretoria, South Africa | July 29 – August 1, 2014

Delayed inoculation

Plant growth measurements

20 40 60 80 100 120 140 10 20 30 40 50

Inoculation date

total plant weight root weight

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2nd International Powdery Scab Workshop | Pretoria, South Africa | July 29 – August 1, 2014

Conclusions

  • Root systems across a wide range of maturities are susceptible

to invasion and follow an equivalent epidemic rate

  • Delaying contact between roots and pathogen delays onset
  • f root invasion
  • Temporal disease level (AUDPC) is decreased
  • This reduces the impact of root invasion on plant growth even

if the level of pathogen in the roots at maturity is the same

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2nd International Powdery Scab Workshop | Pretoria, South Africa | July 29 – August 1, 2014

Conclusions

  • Delayed invasion may reduce the extent of zoosporangia

formation (per root area)

  • The amount of root galling may be similar but onset of galling

is delayed

  • Delayed invasion may also result in reduced tuber disease at

harvest

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2nd International Powdery Scab Workshop | Pretoria, South Africa | July 29 – August 1, 2014

Chemical treatments

  • Inoculum was incorporated prior to planting

(or used natural field infection)

  • Fungicides treatments applied to highly infested seed or to soil

at planting

  • Mancozeb – in furrow spray
  • Mancozeb – seed treatment
  • Shirlan (Fluazinam) – in furrow spray
  • Shirlan (Fluazinam) – seed dip
  • Formalin seed dip
  • Visually clean seed
  • Mini-tubers
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2nd International Powdery Scab Workshop | Pretoria, South Africa | July 29 – August 1, 2014

Chemical treatments

  • Plants were periodically harvested (every 15 days)
  • Disease/pathogen assessments (as before)
  • Zoosporangia score
  • Root gall score
  • Tuber disease score
  • Pathogen quantification (qPCR)
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2nd International Powdery Scab Workshop | Pretoria, South Africa | July 29 – August 1, 2014

Chemical treatments

Content of pathogen (Log (mean Spongospora DNA +1)) in roots – field trials

2 4 6 8 10 12 15 30 45 60 75 Visually clean Mini tubers Infested seed Formalin seed Mancozeb seed Mancozeb soil Shirlan seed Shirlan soil 1 2 3 4 5 6 7 15 30 45 60 75

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2nd International Powdery Scab Workshop | Pretoria, South Africa | July 29 – August 1, 2014

Chemical treatments

Zoosporangia scores – field trials 1&2

0.05 0.1 0.15 0.2 0.25 0.3 15 30 45 60 75 Visually clean Mini tubers Infested seed Formalin seed Mancozeb seed Mancozeb soil Shirlan seed Shirlan soil 0.1 0.2 0.3 0.4 0.5 0.6 15 30 45 60 75

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2nd International Powdery Scab Workshop | Pretoria, South Africa | July 29 – August 1, 2014

Chemical treatments

Root gall scores – field trials 1&2

0.5 1 1.5 2 2.5 3 15 30 45 60 75 Visually clean Mini tubers Infested seed Formalin seed Mancozeb seed Mancozeb soil Shirlan seed Shirlan soil 0.5 1 1.5 2 2.5 3 3.5 15 30 45 60 75

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2nd International Powdery Scab Workshop | Pretoria, South Africa | July 29 – August 1, 2014

Chemical treatments

Tuber disease scores at harvest – field trials 1&2

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2nd International Powdery Scab Workshop | Pretoria, South Africa | July 29 – August 1, 2014

Conclusions

  • Infested seed tubers can provide significant inoculum resulting

in root and tuber disease

  • Planting certified seed or high health mini-tubers is an

important mitigations strategy for both root and tuber disease

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2nd International Powdery Scab Workshop | Pretoria, South Africa | July 29 – August 1, 2014

Conclusions

  • With infested seed - fungicide treatments (to seed and soil)

can reduce root infection

  • They slow the rate of epidemic rather than delaying infection
  • Temporal disease level (AUDPC) is again decreased
  • It can reduce zoosporangial content and galling of roots

(although final levels in mature plants may be similar)

  • And can reduce tuber disease on harvest
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2nd International Powdery Scab Workshop | Pretoria, South Africa | July 29 – August 1, 2014

Conclusions

  • Monitoring root infection dynamics can provide useful model

system to measure impact of disease control treatments

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2nd International Powdery Scab Workshop | Pretoria, South Africa | July 29 – August 1, 2014

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