Potato star scab

Potato star scab is a widespread soil-borne disease caused by the bacterium Streptomyces stelliscabiei. This pathogen belongs to the actinomycetes group and survives in the soil by colonizing organic debris. It is a persistent infection that compromises the quality of harvested tubers, leading to significant economic losses for potato producers globally.

The primary host for this pathogen is the potato crop. While the bacteria primarily infect the developing tubers, they can also affect stolons and roots. Infection typically occurs during the early stages of tuber formation, when the periderm is still vulnerable, allowing the bacteria to penetrate the skin and colonize the tissues.

The characteristic symptoms include star-shaped lesions on the tuber surface. These lesions are typically raised, corky, and crater-like, exhibiting a star-patterned cracking. Unlike common scab, the lesions caused by Streptomyces stelliscabiei tend to be more invasive and can lead to severe superficial damage that drastically reduces the marketability and storage life of the potato crop.

The development of the disease is highly dependent on environmental conditions. It thrives in warm, dry soils with a neutral to alkaline pH (pH 6.0–7.5). Poorly aerated soils are not a primary concern, as these bacteria are aerobic; however, excessive irrigation during tuber initiation can help suppress the symptoms, whereas dry conditions promote the activity and spread of the pathogen.

Management of potato star scab requires an integrated agricultural strategy. Key tactics include the use of certified, disease-free seed potatoes and the selection of resistant cultivars. Soil management is equally critical: applying sulfur-based fertilizers to lower soil pH can significantly reduce the severity of the infection. Furthermore, long-term crop rotation with non-host crops helps to decrease the population of the pathogen in the soil.