Common scab of potato

Streptomyces venezuelae is a soil-inhabiting actinomycete known to be a causative agent of common scab, a widespread disease affecting potatoes and various root vegetables. This pathogen is highly persistent, capable of surviving in the soil for long periods by utilizing organic matter, which makes it a challenging threat to agricultural fields.

The primary hosts of this pathogen include potato tubers, sugar beets, radishes, and carrots. In potato production, the infection primarily targets the skin of developing tubers. Although the disease does not usually penetrate deep into the tuber flesh, it causes significant cosmetic damage, leading to heavy losses in marketability and quality.

The symptoms are visually distinct, manifesting as lesions on the tuber surface. These can appear as flat, raised, or deep pitted scabs. As the tubers mature, the infected areas become corky and necrotic. These lesions serve as entry points for secondary pathogens, significantly increasing the risk of rot during storage or transportation.

Disease development is highly dependent on environmental conditions. Streptomyces venezuelae thrives in well-aerated, warm soils (20–30°C) with a neutral to alkaline pH. Practices such as heavy liming or the application of fresh manure increase the soil pH, creating an environment that is highly favorable for the proliferation of this actinomycete.

Management and prevention focus on maintaining optimal soil conditions. Farmers are advised to avoid over-liming fields and to use acid-forming fertilizers to keep the soil pH slightly acidic, which suppresses the pathogen. Furthermore, implementing crop rotations with cereals and ensuring sufficient soil moisture during the crucial tuber-initiation stage are essential for limiting the incidence of common scab.