Black Dot Some questions and answers

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Black Dot Some questions and answers

• Arcadio Viveros Guzmán
• Doug Waterer
• Jill Thomson
• Department of Plant Sciences
• University of Saskatchewan
• SSPGA Field Day
• Outlook
• 16 August 2007

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Arcadio Viveros Guzmán

• Education
• B.Sc. Agronomy
• M.Sc. Tropical Agroecology

• Research interests
• IPM for vegetable production
• Sustainable disease management

Veracruz State
Jalapa
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Thesis goals

• General objective
• To enhance the health of Canadian seed potatoes,
  especially those designated for export to Mexican
  seed markets.
• Specific objectives
• To survey seed potatoes in Saskatchewan for
  incidence and severity of silver scurf and black
  dot.
• To examine the relative sensitivity of cultivars
  to silver scurf, black dot and rhizoctonia.
• To evaluate fungicides for control of silver
  scurf, black dot and rhizoctonia on seed and
  table potatoes.
• To evaluate botanical oils with potential
  antifungal activity for control of silver scurf,
  black dot and rhizoctonia on seed and table
  potatoes

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• Integrated control of fungal diseases of seed and
  table potatoes in Saskatchewan

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Black dot
Symptoms Foliage

• Previously not considered important because
• Typically invades plants stressed by lack of
  fertilizer or water, weed competition, etc.
• Often acts in combination with other pathogens
• In UK is now considered economically important
• All blemish diseases are more important due to
  pre-market washing
• Sclerotia are found on tuber skin also on below
  ground stems

Verticillium wilt
British Potato Council www.potato.org.uk
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Symptoms Tubers
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Symptoms Stems
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Symptoms Main stems below the ground
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Symptoms Roots
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Silver scurf Black dot
Silver scurf
(After incubation _at_ high humidity)
Black dot
Silver scurf
Spores
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Questions?

• Is Black dot present in Saskatchewan?
• How common is it on seed lots?
• How often does it occur on different parts of the
  plant?
• What impact does it have on yield?
• How can it be controlled?

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How can we answer these questions?

• Survey of seed tubers disease levels in
  cultivars, generations, locations (2 seasons)
• Survey of plants before top kill (Summer 2007)
• Disease levels by generation
• Evaluation of efficacy of fungicides

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Survey of seed tubers Winter 2007

• 30-tuber samples from the earliest latest
  seed generation in the farm.
• Assess Rhizoctonia, Common scab Powdery
  scab
• Incubate for 3 weeks _at_ high humidity
• Assess Silver scurf Black dot

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Sampling of seed tubers across Saskatchewan
Results of seed survey 1
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Participation

• 11 Seed growers from 9 locations

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Overall incidence of disease on tubers from
Saskatchewan seed-potato farms 2007
Results derived from all cultivars, seed
generations and locations combined. Total of 83
samples
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Overall severity of disease on tubers from
Saskatchewan seed-potato farms 2007
Results derived from all cultivars, seed
generations and locations combined. Total of 83
samples
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Overall incidence of disease by cultivar on
tubers from Saskatchewan seed-potato farms 2007
Results derived from all seed generations and
locations combined.
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Overall disease incidence on tubers in all the
cultivars (31) and all the samples (83) per seed
generation
Number of samples per seed generation PE35
E115 E228 E32 E42 and F1
Severity follows the same pattern
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Disease levels in the cultivar Norland per seed
generation
Cultivar Norland comprises 14 samples classified
in different variations such as Norland
Wisconsin, DR Norland, Red Norland and
Norland. First set of three columns indicates
incidence, and the second set of three columns,
severity for each disease Number of samples per
seed generation PE6 E14 E24
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Disease levels in the cultivarRusset Burbank per
seed generation
Cultivar Russet Burbank comprises 17 samples
distributed as follows PE8 E13 and
E26. First set of three columns indicates
incidence, and the second set of three columns,
severity for each disease
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Field survey Sampling of foliage, stems, roots,
Summer 2007

• Objective
• To determine the relationship between the seed
  infestation levels of silver scurf, black dot
  rhizoctonia assessed in the seed survey and the
  resulting levels of disease on the crop
• Method
• Sample 5 plants from Norland Russet Burbank
  plantings of the earliest latest generations on
  individual farms.
• Assess for disease levels on foliage
  below-ground parts of plant

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Field survey Sampling of plants in seed farms
in Saskatchewan, Summer 2007
Plant sample Main stems, root system, stolons
Poly bag containing 2 of the larger tubers
Paper bag containing 3 diseased compound leaves
and 1 healthy compound leaf
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Second seed survey Fall and Winter 2007

• Objective
• To determine the relationship between the seed
  infestation levels of silver scurf, black dot
  rhizoctonia assessed in the 1st survey and the
  resulting levels of disease on the crop.
• Method
• 30-tuber sample from the earliest and latest
  generation of the cultivars Norland Russet
  Burbank

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Questions?

• Is Black dot present in Saskatchewan?
• How common is it on seed lots?
• How often does it occur on different parts of the
  plant?
• What impact does it have on yield?
• How can it be controlled?

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Answers!

• Black dot is present on Saskatchewan potatoes
• It often occurs on seed lots
• Levels are generally low
• Can be found on below-ground stems, roots and
  tubers

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Acknowledgements

• SSPGA
• Co-operators
• Gert Kruger

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Thank you very much!

• Questions?