Potato scab

Streptomyces caviscabies is a specific species of soil-borne actinomycetes recognized as a significant pathogen responsible for deep-pitted potato scab. This bacterium survives primarily in the soil, utilizing organic matter and debris as reservoirs during the periods between potato cultivation cycles.

The primary host for this pathogen is the potato, where it attacks developing tubers. While it primarily targets potato crops, the pathogen exhibits a broad host range, occasionally affecting other root crops such as radishes or beets. The infection usually initiates through tuber lenticels or small mechanical abrasions on the skin.

Symptoms of the disease manifest as deep, necrotic, crater-like lesions on the surface of the tubers. Unlike common scab, the lesions caused by S. caviscabies are noticeably deeper and can affect the marketability of the crop, often leading to total rejection of batches due to the unsightliness and potential for secondary rot development.

Environmental conditions play a decisive role in the disease cycle. The pathogen thrives in alkaline or neutral soils (pH 5.5 and above) and is particularly virulent in well-aerated, sandy soils with moderate moisture levels. High temperatures during the tuber initiation phase are critical factors that accelerate the rapid colonization of tuber tissues.

Effective management requires an integrated approach. Farmers should focus on maintaining soil pH levels below 5.5, which is often sufficient to inhibit bacterial growth. Crop rotation with non-host crops, such as cereal grains, and the application of green manure crops are essential practices to reduce the concentration of the inoculum in the soil profile.