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Specialist opinion: Common scab revisited

In 2017 and 2018 Dr Eugenia Banks, Potato Specialist with the Ontario Potato Board in Canada, conducted common scab research on potatoes that included the identification of the common scab bacteria present in Ontario potato fields.  Dr Banks sampled 50 fields and submitted the soil samples to A & L Laboratories. A&L identified the different scab bacterium species using PCR.

The results of the PCR tests indicated that Streptomyces stelliscabiei was the most common bacteria found followed by S. scabiei.  The lab also found that the higher the organic matter (OM) in the soil samples, the lower the levels of S. stelliscabiei.  (This research was supported by the Ontario Potato Board).

Dr Banks says Streptomyces caviscabies is a common scab bacterium that causes deep, star-shaped lesions (see photo below).  Growers have told Dr Banks that this is “sickening”  because often there is just one lesion that renders the tuber unmarketable.  Streptomyces caviscabies was described for the first time by Quebec researchers in 1996.

Sometimes there is fine starring or netting on tubers (see photo below).  This problem is more common on red varieties in warm years, according to Dr Banks. She says Neil Gudmestad, a NDSU Distinguished Professor (retired), thinks it is a form of netted scab, perhaps caused by Streptomyces reticuliscabiei, but at this stage “it is just a guess”.

“It usually causes a much finer netting, but in more susceptible varieties I think it could be more severe with deeper netting,” Dr Banks says. 

The third photo (below) shows a tuber that Dr Banks left on the ground after taking a picture of pink eye.  She was back in the field 3-4 days later and noticed that the pink eye had dried up leaving star-shaped lesions.

Source: Dr Eugenia Banks
Email: [email protected]
Cover photo: Dr Eugenia Banks at the Ontario Potato Board Field Day (2016) | Courtesy Brad Pritchard/Metroland

Lukie Pieterse, Editor and Publisher of Potato News Today

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