Common scab of potato

The causative agent of this disease is Streptomyces acidiscabies, a soil-inhabiting actinomycete that is widespread in agricultural fields. This pathogen is saprophytic by nature, allowing it to survive in the soil for years on organic matter independently of the host plant, which presents a major challenge for crop rotation.

Potatoes are the primary host for this pathogen, but it also affects a wide range of root crops, including beets, radishes, and carrots. The bacteria infect the plants primarily through the lenticels on developing tubers or through mechanical wounds, causing significant localized damage during the early stages of tuber formation.

Symptoms appear as various types of lesions on the tuber surface, which may be superficial, raised, or deep, depending on the cultivar and environmental factors. These lesions are typically corky in appearance and can cover large areas of the tuber, significantly reducing its commercial value and increasing its susceptibility to moisture loss during storage.

The development of Streptomyces acidiscabies is strongly favored by dry soil conditions and a neutral to alkaline soil pH (ranging from 6.0 to 8.0). Because the pathogen thrives in these conditions, excessive liming of the field before planting potatoes is a primary factor in promoting severe outbreaks of the disease in susceptible areas.

Control strategies must be integrated, focusing on crop rotation, the use of resistant potato varieties, and effective irrigation management during the tuberization period. Additionally, applying acidifying fertilizers can help lower soil pH to levels that are less favorable for the pathogen, thereby reducing the incidence and severity of common scab.