Common scab

Common scab is a destructive plant disease caused by actinomycetes of the genus Streptomyces, most notably Streptomyces scabies. It is a soil-borne pathogen that primarily affects the tubers, roots, and stolons of potato plants, causing significant economic losses for farmers worldwide.

The disease infects various root crops, including potatoes, beets, carrots, and radishes. The bacteria are ubiquitous in soil and can persist for many years, surviving on organic matter or in the form of spores that wait for favorable conditions to infect host tissues.

The symptoms of common scab manifest as lesions on the tuber skin, which can range from shallow, corky scabs to deep, pitted craters or raised, warty lesions. While the inside of the tuber usually remains edible, the presence of these lesions makes the produce unmarketable, reduces storage quality, and decreases the overall crop value.

The development and spread of Streptomyces are heavily influenced by environmental conditions, particularly soil pH and moisture. The disease is most severe in alkaline or neutral soils (pH above 5.5) and under dry soil conditions during the early stages of tuber initiation. High soil temperatures also promote the activity of these pathogens.

Management and prevention strategies are essential for controlling common scab:

• Selecting resistant potato cultivars for cultivation.
• Maintaining soil pH between 5.0 and 5.2.
• Utilizing proper crop rotation with non-host crops.
• Ensuring adequate soil moisture during the critical tuber-setting period.
• Applying pathogen-free certified seed tubers to prevent introduction into the field.