Streptomyces scabies (Streptomyces cremeus)

Streptomyces cremeus is a soil-borne filamentous bacterium known for causing common scab disease in various tuberous and root crops. These actinomycetes are ubiquitous in agricultural soils, where they survive by decomposing organic matter. Under specific conditions, they infect the periderm of developing tubers and roots, leading to the formation of characteristic necrotic lesions that degrade the crop's market value.

The primary hosts for this pathogen include potatoes, sugar beets, carrots, and radishes. The bacteria infect the plant by entering through lenticels, wounds, or the points where lateral roots emerge. Once inside the tissue, the pathogen secretes enzymes that break down the plant cell walls, leading to the typical scab-like appearances on the skin of the harvestable crop.

Symptoms of the infection vary depending on the host and the severity of the outbreak. Key visible signs include:

• small, circular brown lesions on the surface;
• corky or scabby patches of tissue that may merge;
• pitted or deep-seated sores in severe cases;
• significant reduction in storage stability and aesthetic quality.

The development and spread of Streptomyces cremeus are heavily influenced by the edaphic environment. The pathogen thrives in alkaline to neutral soils with a pH ranging between 6.5 and 8.0. Furthermore, dry and warm soil conditions during the tuberization stage significantly exacerbate the disease incidence. Proper moisture management during the early stages of tuber formation is critical to limiting the infection's success rate.

Effective management requires an integrated strategy to minimize pathogen impact. Farmers are encouraged to maintain slightly acidic soil conditions to suppress bacterial growth and to implement long-term crop rotation schemes. Using pathogen-free seed potatoes is a foundational requirement, along with the application of antagonistic biological agents and green manure cover crops to improve soil microbial diversity and suppress harmful actinomycetes.