Streptomyces  spp.

Common scabies

( Common scab and Netted scab )

Description 

Common scabs are caused by bacteria belonging to the genus Streptomyces , belonging to the group of Actinomycetes (heterotrophic bacteria that form a filamentous structure) and live in the soil.

There are 2 main types of symptoms of common scab (pustule and cork) which are currently considered as two different diseases due to the causative agent, the climatic conditions of development and the varietal sensitivity.

- Common scabies in pustule or raised form is caused by several species of Streptomyces pathogenic In France, at least three species are responsible for this symptom: Streptomyces scabiei, S. europaeiscabiei, S. stelliscabiei . Other species have been described around the world ( S. acidiscabies, S. turgidiscabies , etc.).

Risk factors

The soil is the main source of inoculum because Streptomyces live in the soil with or without the presence of host plants.

Infection occurs through the lenticels of the tubers at the time of tuber formation and the disease does not progress in storage. In general, common scabs are favored by light and airy soils.

Disease expression depends on the variety used (varieties are susceptible to varying degrees), temperature (thermal optimum 19-24°C) and soil moisture (disease favored by dry conditions) .

Biological control  

• Choose varieties that are resistant (cork scab) or not very sensitive (pustule scab),
• Avoid favorable precedents (beets, carrots, radishes, etc.) or the supply of poorly decomposed organic matter,
• Avoid light soils or soil preparations favoring soil aeration,
• Limit the addition of lime amendments just before potato cultivation,
• Assess the risk at plot level using trap plants,
• Irrigate to saturate the soil at the time of tuber initiation (to limit pustule scab),
• Lengthen the rotations (cork scabies).