Phytophthora Root

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Phytophthora Root Stem Rot of Soybean
Phytophthora biology
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How Does Disease Develop?
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Phytophthora diseases

• Early Season
• Seed rot
• Damping-off
• Pre-emergence
• Post emerge
• Associated with rainfall soon after planting
• Root and stem rot
• Associated with midseason rainfall events

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Phytophthora sojae phases
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Seed Seedling diseases
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Losses from P. sojae
reduced stand and/or replant costs
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Phytophthora root stem rot
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Phytophthora root stem rot

• Environmental conditions
• Warm, wet soils
• Compacted soils
• Poorly drained soils
• Usually appears early to mid-July
• May be worse in no-till due to the longer period
  of time soils remain wet

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Phytophthora root rot

• What is Phytophthora sojae?
• A unique water-loving microorganism
• Sometimes called water molds
• Related to Pythium and algaes
• Infection process
• Overwinter as oospores
• Germinates to form a swollen vesicles (sporangia)
• Zoospores released

25µm
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Phytophthora root rot

• Infection Process
• Zoospores liberated
• Swims to root
• Encysts on plant surface
• Germinates and forms appressorium
• Penetrates host tissue
• Threadlike mycelium of the pathogen grows between
  and through cells of the plant (inter and
  intracellularly)

Zoospores swimming around a fine root
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Phytophthora sojae diseases

• Date of disease onset and severity determined by
• Precipitation and temperature
• Resistance levels in varieties
• Management decisions are
• Host resistance
• Chemical management
• Site dependent

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• Produced in cooperation with
• North Central Soybean Research Program
• QSSBs in NC states
• Iowa State University
• Kansas State University
• Michigan State University
• University of Minnesota
• University of Missouri
• University of Nebraska-Lincoln
• North Dakota State University
• The Ohio State University
• Ontario Ministry of Agriculture and Food
• Purdue University
• South Dakota State University
• USDA-ARS

Click here to link to the next Phytophthora
lesson Phytophthora Genetics and Host Resistance