Powdery scab

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Sporosori

Powdery scab is a plant disease that affects potatoes and other members of the Solanaceae family. It is caused by the pathogen Spongospora subterranea, a type of plasmodiophorid.

Symptoms

The primary symptom of powdery scab is the appearance of raised, pustule-like lesions on the surface of the tubers. These lesions eventually burst, releasing a powdery mass of spores. Infected tubers may also exhibit root galls and stunted growth. The disease can significantly reduce the marketability of the crop due to the unsightly appearance of the tubers.

Pathogen

Spongospora subterranea is a soil-borne pathogen that thrives in cool, wet conditions. It is a member of the Plasmodiophoromycota and is closely related to the pathogen that causes clubroot in cruciferous vegetables. The pathogen produces resting spores that can survive in the soil for many years, making it difficult to eradicate once it has become established in a field.

Life Cycle

The life cycle of Spongospora subterranea involves several stages. The resting spores germinate in the presence of a suitable host, releasing zoospores that infect the roots of the plant. The pathogen then forms a plasmodium within the root cells, which eventually produces new resting spores. These spores are released into the soil when the infected tissue decays, completing the cycle.

Management

Managing powdery scab involves a combination of cultural practices and, in some cases, chemical treatments. Key strategies include:

• **Crop rotation**: Avoid planting potatoes or other susceptible crops in the same field for several years.
• **Resistant varieties**: Use potato varieties that are less susceptible to powdery scab.
• **Soil management**: Improve soil drainage and avoid over-irrigation to reduce the conditions that favor the pathogen.
• **Sanitation**: Clean and disinfect equipment and storage facilities to prevent the spread of the pathogen.

Economic Impact

Powdery scab can have a significant economic impact on potato production. The disease not only reduces yield but also affects the quality of the tubers, leading to lower market prices. In severe cases, entire crops may be deemed unmarketable.

See Also

• Potato diseases
• Plant pathology
• Soil-borne diseases