Powdery Mildews

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Powdery Mildews
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Powdery Mildews

• Foliage, stems, flower, fruit diseases
• Characteristic gray, powdery growth on
• infected plant parts
• Distortion of host tissue
• Small, black structures may appear
• ascocarps ( cleistothecia)
• Obligate parasites

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Mycelium Conidia
Powdery Mildew of Pea Cherry
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Ascocarps (cleistothecia) on host
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Powdery Mildew of Wheat
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• Genera are distinguished by
• 1) appendages on the cleistothecium
• 2) number of asci inside each cleistothecium

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Ascocarp appendages

• Mycelioid resemble hyphae, indefinite
• eg. Erysiphe, Blumeria, Sphaerotheca

2) Rigid bulbous base and pointed tips
eg. Phyllactinia
3) Rigid curled tips eg. Uncinula
4) Rigid dichotomously branched tips eg.
Microsphaera, Podosphaera
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mycelioid
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One ascus per ascocarp Sphaerotheca Podosphaera
- mycelioid
- dichotomously branched
Several asci per ascocarp Erysiphe Microsphaera Un
cinula Phyllactinia
- mycelioid
- dichotomously branched
- curled tips
- bulbous base
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One ascus per ascocarp
Podosphaera
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More than one ascus per ascocarp
Uncinula
http//www.pacificcoast.net/mycolog/chapter4e.htm
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Chains of conidia
http//www.pacificcoast.net/mycolog/chapter4e.htm
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Powdery Mildew Lifecycle
Haustoria penetrate the host epidermal cells
directly
primary
secondary
APSnet
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Blumeria graminis haustorium in epidermal cell
L.M. Carris
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Powdery Mildew of Rose

• Causal agent Sphaerotheca pannosa
• Worldwide occurrence - both field- and
  greenhouse-grown roses
• Disease cycle differs between field and greenhouse

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Powdery Mildew of Rose
Symptoms signs

• Most common on young, succulent tissues
• Small, blister-like lesions
• Gray powdery growth on infected plant parts
• Distortion
• Cleistothecia

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Powdery Mildew of Rose
http//cygnus.tamu.edu/Texlab/Shrubs/Rose/rsp.html
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Powdery Mildew Disease Cycle for Rose
2 Cycles
http//www.ipm.ucdavis.edu/PMG/PESTNOTES/pni7493-2
.html
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Powdery Mildew Diseases
Environmental factors

• Warm, dry weather diseases
• High relative humidity sufficient
• Free water NOT required for conidial germination
  or penetration of plant
• Sporulation requires dew
• Cool autumn weather stimulates cleistothecium
  development

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Powdery Mildew Diseases
Control

• 1. Foliar Fungicides
• sulfur-containing, systemic
• 2. Disease-resistant varieties
• 3. Sanitation
• removal of infested plant debris

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Todays Exercises

• Powdery Mildews
• - collecting trip to obtain fresh material
• - observe signs and symptoms
• - make mounts and observe ascocarps
• Previous labs works
• - examine the fruits (lab2)
• - observe the wheat and grass roots (lab3)
• - record the results of tests (lab4)