Common scab of potato

The causal agent of common potato scab is Streptomyces lavendulae, a soil-inhabiting bacterium classified among actinomycetes. These microorganisms are primarily saprophytic, thriving on decaying organic matter within the soil, but they adapt as parasites when environmental conditions allow them to infect the underground parts of host plants.

While potatoes are the most economically significant host for this pathogen, it can also affect other root vegetables such as beets, carrots, and radishes. Streptomyces lavendulae invades the host tissue through lenticels, stomata, or small wounds during the rapid growth phase of tubers, leading to the establishment of the infection.

Symptoms of the disease manifest as characteristic scab lesions on the surface of tubers. These lesions can vary in appearance, ranging from superficial scabs to deep pits or raised, corky structures. Such defects significantly compromise the marketability of the produce, as the skin becomes rough, disfigured, and unsightly, which may also facilitate entry for storage rots.

The development of common scab is strongly influenced by environmental factors. High soil pH (alkaline or neutral), elevated temperatures, and low soil moisture levels during tuber initiation are the primary drivers of infection. Because the bacteria can survive for many years in the soil independently of a host plant, eradication is extremely difficult once the pathogen is established in a field.

Prevention and management require integrated strategies to minimize the impact of the disease. Key measures focus on modifying soil conditions and utilizing host resistance:

• Applying physiological acidic fertilizers to lower soil pH.
• Maintaining adequate soil moisture during the tuberization period.
• Implementing crop rotation with non-host crops.
• Selecting potato varieties known for their resistance to actinomycete scab.