Root and stem rots, cankers

Featured Pathogens

Phytophthora spp. (Oomycete)

1. Phytophthora infestans
2. Phytophthora parasitica

Root and stem rots, cankers

Phytophthora, Sclerotium rolfsii, and Fusarium solani

Symptoms

1. Root necroses (root rots)
2. Stem cankers, stem girdling
3. Foliar necroses (blights)
4. Tuber rot (potato late blight)

Root and Stem Rots, Cankers

Featured Pathogens

Sclerotium rolfsii (Deuteromycete)

Root and Stem Rots, Cankers

Featured Pathogens

Fusarium solani (Deuteromycete)

Root and Stem Rots, Cankers

Featured Pathogens

Plasmodiophora brassicae (Myxomycete, a protozoan plant pathogen)

• P. brassicae causes clubroot; the causal agent is an obligate parasite

Root and stem rots, cankers

Plasmodiophora brassicae

Symptoms

Are conspicuous root gall, no necrosis

Root and stem rots, cankers

Phytophthora

Signs

Pale, moist mycelium

Root and stem rots, cankers

Sclerotium rolfsii

Signs

White mycelium spherical sclerotia

Root and stem rots, cankers

Fusarium solani

Signs

Signs not evident

Root and stem rots, cankers

Plasmodiophora brassicae

Signs

Signs not evident

Root and stem rots, cankers

Phytophthora (like pythium)

Life cycles and structures

1. Moderate host ranges
2. Prefers cool, wet conditions
3. Sporangia (inoculum dispersal) Germinate directly or Produce zoospores
4. Oospores (dormancy)

• Antheridia
• Oogonia

Root and stem rots, cankers

Sclerotium rolfsii (like Rhizoctonia)

Life cycles and structures

1. Very wide host range
2. Mycelium white (no 90 degree branching)
3. Truly a hot-weather pathogen)
4. Asexual stage without spores
5. Sexual stage (Basidiomycota)
6. No conidia

Root and stem rots, cankers

Fusarium solani

Life cycles and structures

1. Moderately wide host range
2. Asexual stages (macro-, microconidia, chlamydospores)
3. Sexual stage (Ascomycota)

Root and stem rots, cankers

Plasmodiophora brassicae

Life cycles and structures

1. Very restricted host range (and a disease of northern climates)
2. Produces an intracellular plasmodium
3. Plasmodium breaks up into zoospores
4. Require acidic soils, can be controlled by raising pH to about 7.2 or higher

Root and stem rots, cankers

Controls

1. Fungicides: Methyl bromide, Mercurials, Metalaxyl (Oomycota), Bordeaux mixture (Oomycota)
2. Sterile pots, soil
3. Avoid contamination (e.g. hoses)
4. Avoid overwatering
5. Crop rotation

1. Disease forecasting (late blight)
2. Use certified planting stock