Soil rot of sweet potato

Soil rot, also known as pox, is a devastating disease of sweet potatoes caused by the bacterium Streptomyces ipomoeae. This soil-borne pathogen specifically targets the root system and underground parts of the plant, often leading to severe economic losses for farmers.

The primary host for this pathogen is the sweet potato. While some other plant species might occasionally show symptoms, the economic impact is focused entirely on sweet potato production. The pathogen survives in the soil as a saprophyte, allowing it to persist for long periods even in the absence of a host crop.

Symptoms of the disease are characterized by dark, sunken lesions on the storage roots. These lesions result in stunted, deformed roots that often snap off during harvesting. Above ground, the plants may appear stunted, chlorotic, and show signs of significant vigor loss compared to healthy crops.

The development of the disease is highly influenced by soil environmental conditions. Streptomyces ipomoeae thrives in soils with a pH above 5.2 and moderate soil moisture levels. High temperatures during the growing season further accelerate the activity of the bacteria, leading to widespread infection across the field.

Management of soil rot is difficult once the pathogen is established. Key strategies include:

• Implementing long-term crop rotation to reduce inoculum levels.
• Maintaining soil pH below 5.2 to suppress bacterial activity.
• Using certified, disease-free planting material to avoid introducing the pathogen.
• Practicing strict field sanitation to prevent the spread of contaminated soil.