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, South Africa | July 29 – August 1, 2014
UTAS 2 nd International Powdery Scab Workshop | Pretoria, South Africa | July 29 – August 1, 2014
Outline 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 2 nd International Powdery Scab Workshop | Pretoria, South Africa | July 29 – August 1, 2014
Outline 2 nd International Powdery Scab Workshop | Pretoria, South Africa | July 29 – August 1, 2014
Outline 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 • 2 nd 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 2 nd 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 • Tasmanian processors estimate yield losses of 10-20% regularly occur 2 nd 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 2 nd 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 2 nd 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 • 2 nd International Powdery Scab Workshop | Pretoria, South Africa | July 29 – August 1, 2014
Delayed inoculation Content of pathogen (Log (mean Spongospora DNA +1)) in roots At emergence 10 DAE 20DAE 30 DAE 40 DAE 50 DAE 100000 10000 Log DNA content 1000 100 10 1 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 115 120 10 000 000 1 000 000 100 000 10 000 1 000 100 10 1 15 30 45 60 75 90 105 2 nd International Powdery Scab Workshop | Pretoria, South Africa | July 29 – August 1, 2014
Delayed inoculation Root gall and Zoosporangia scores At emergence 10 DAE 20DAE 30 DAE 40 DAE 50 DAE 1.4 1.2 1 Root gall score 0.8 0.6 0.4 0.2 0 0.5 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 115 0.45 Zoosporangia score 0.4 0.35 0.3 0.25 0.2 0.15 0.1 0.05 0 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 115 2 nd International Powdery Scab Workshop | Pretoria, South Africa | July 29 – August 1, 2014
Delayed inoculation Tuber disease scores at harvest 3.5 Tuber disease score (0-6) 3 2.5 2 1.5 1 0.5 0 0 10 20 30 40 50 Inoculation date 2 nd International Powdery Scab Workshop | Pretoria, South Africa | July 29 – August 1, 2014
Delayed inoculation Plant growth measurements 140 total plant weight root weight 120 100 80 60 40 20 0 0 10 20 30 40 50 Inoculation date 2 nd 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 of 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 2 nd 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 2 nd 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 • 2 nd 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) • 2 nd 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 12 Visually clean Mini tubers Infested seed 7 Formalin seed Mancozeb seed Mancozeb soil Shirlan seed Shirlan soil 10 6 5 8 4 6 3 4 2 2 1 0 0 15 30 45 60 75 15 30 45 60 75 2 nd International Powdery Scab Workshop | Pretoria, South Africa | July 29 – August 1, 2014
Chemical treatments Zoosporangia scores – field trials 1&2 Visually clean Mini tubers Infested seed Formalin seed Mancozeb seed Mancozeb soil 0.3 Shirlan seed Shirlan soil 0.6 0.25 0.5 0.2 0.4 0.15 0.3 0.1 0.2 0.05 0.1 0 0 15 30 45 60 75 15 30 45 60 75 2 nd International Powdery Scab Workshop | Pretoria, South Africa | July 29 – August 1, 2014
Chemical treatments Root gall scores – field trials 1&2 Visually clean Mini tubers Infested seed Formalin seed Mancozeb seed Mancozeb soil Shirlan seed Shirlan soil 3 3.5 3 2.5 2.5 2 2 1.5 1.5 1 1 0.5 0.5 0 0 15 30 45 60 75 15 30 45 60 75 2 nd International Powdery Scab Workshop | Pretoria, South Africa | July 29 – August 1, 2014
Chemical treatments Tuber disease scores at harvest – field trials 1&2 2 nd 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 2 nd 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 2 nd 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 2 nd International Powdery Scab Workshop | Pretoria, South Africa | July 29 – August 1, 2014
http://www.appsnet.org/asds/ 2 nd International Powdery Scab Workshop | Pretoria, South Africa | July 29 – August 1, 2014
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