Know more

Our use of cookies

Cookies are a set of data stored on a user’s device when the user browses a web site. The data is in a file containing an ID number, the name of the server which deposited it and, in some cases, an expiry date. We use cookies to record information about your visit, language of preference, and other parameters on the site in order to optimise your next visit and make the site even more useful to you.

To improve your experience, we use cookies to store certain browsing information and provide secure navigation, and to collect statistics with a view to improve the site’s features. For a complete list of the cookies we use, download “Ghostery”, a free plug-in for browsers which can detect, and, in some cases, block cookies.

Ghostery is available here for free:

You can also visit the CNIL web site for instructions on how to configure your browser to manage cookie storage on your device.

In the case of third-party advertising cookies, you can also visit the following site:, offered by digital advertising professionals within the European Digital Advertising Alliance (EDAA). From the site, you can deny or accept the cookies used by advertising professionals who are members.

It is also possible to block certain third-party cookies directly via publishers:

Cookie type

Means of blocking

Analytical and performance cookies

Google Analytics

Targeted advertising cookies


The following types of cookies may be used on our websites:

Mandatory cookies

Functional cookies

Social media and advertising cookies

These cookies are needed to ensure the proper functioning of the site and cannot be disabled. They help ensure a secure connection and the basic availability of our website.

These cookies allow us to analyse site use in order to measure and optimise performance. They allow us to store your sign-in information and display the different components of our website in a more coherent way.

These cookies are used by advertising agencies such as Google and by social media sites such as LinkedIn and Facebook. Among other things, they allow pages to be shared on social media, the posting of comments, and the publication (on our site or elsewhere) of ads that reflect your centres of interest.

Our EZPublish content management system (CMS) uses CAS and PHP session cookies and the New Relic cookie for monitoring purposes (IP, response times).

These cookies are deleted at the end of the browsing session (when you log off or close your browser window)

Our EZPublish content management system (CMS) uses the XiTi cookie to measure traffic. Our service provider is AT Internet. This company stores data (IPs, date and time of access, length of the visit and pages viewed) for six months.

Our EZPublish content management system (CMS) does not use this type of cookie.

For more information about the cookies we use, contact INRA’s Data Protection Officer by email at or by post at:

24, chemin de Borde Rouge –Auzeville – CS52627
31326 Castanet Tolosan CEDEX - France

Dernière mise à jour : Mai 2018

Menu logoprincipal INRA logo gnis Potato dynamics LTD ARVALIS FN3PT GERMICOPA

Potato tuber blemishes: understanding & diagnosis

Common scab

Bacteria, Actinomycete

Latin name : Streptomyces spp.


Diagnostic characters for visual diagnosis

Three main types of cork-like lesions including shallow, raised and deep pitted lesions

  • Shallow  scab: superficial, roughened lesions  often slightly invading below the neighbouring healthy skin
  • Raised or erumpent scab: lesions are slightly raised above surrounding peridermal tissue. They may coalesce forming large scabby areas
  • Deep or pitted scab: craters which may be 1 to 10 mm deep, roughly circular or sometimes star-shaped lesions, up to 10 mm in diameter


Notes on confirmatory diagnostics

To confirm the diagnostic, different steps must completed because some saprophytic strains might be isolated together with the pathogenic ones :

  • Isolation of Streptomyces strains on water agar or on other semi selective medium,
  • Selection of the pathogenic strains by testing their pathogenicity on radish (radish is susceptible to common scab, the test is reliable, easy and quick) or/and amplifying the TaxAB gene present only in pathogenic strains
  • Identification  of the species associated with the lesions by sequencing the 16S rRNA gene or by using species-specific primers


Specific references :

Bouchek-Mechiche etal (2000 b). Plant Pathology, 49, 3-10

Lehtonen et al (2004). Plant Pathology, 53(3), 280–287

Wanner, L.A (2004). Plant Disease, 88, 785-796

Wanner, L.A (2006). Phytopathology, 96, 1363-1371

more symptoms

Possible confusing symptoms :