Common scab of potato

Common scab is a widespread disease caused by the soil-borne actinomycete Streptomyces albidoflavus. These bacteria are saprophytic in nature, thriving on decaying organic matter in the soil, but they can opportunistically infect potato tubers and other root crops when environmental conditions favor their development.

The primary host for this pathogen is the potato, but it is also known to affect carrots, beets, parsnips, and radishes. The infection typically gains entry to the tubers through lenticels, natural fissures, or wounds created by soil insects and mechanical damage. Once established, the bacteria disrupt the normal skin development of the tuber.

Visible symptoms include corky lesions on the tuber surface, which can vary significantly in appearance. They may appear as superficial scabs, raised bumps, or deep, pitted cavities. While the damage is primarily cosmetic and does not typically affect the internal quality or taste of the potato, it significantly reduces market value and consumer appeal.

The development of common scab is strongly correlated with soil conditions. Alkaline or neutral pH levels (above 5.5) promote the growth and virulence of Streptomyces albidoflavus. Additionally, periods of low soil moisture during the critical stage of tuber initiation are highly conducive to disease outbreaks, as dry soil allows the pathogen to colonize the tuber surface more effectively.

Effective management requires an integrated strategy centered on soil pH regulation and cultural practices. Applying acidifying fertilizers can help suppress the pathogen's activity. Crop rotation involving non-susceptible crops is essential to reduce inoculum levels in the soil. Furthermore, maintaining consistent soil moisture during the tuberization period can significantly limit the incidence of the disease.