Photo courtesy of Eugenia Banks

An Ontario research project on common scab in potatoes, supported by the Ontario Potato Board, has yielded surprising results. The fact that S. stelliscabiei is the most common species and not S. scabiei as expected is a major breakthrough according to Eugenia Banks, consultant to the Ontario Potato Board. 

“It could lead to development of practices that specifically target this species,” she reported to the Ontario Potato Conference on March 6.  “This is a two-year project and will be completed in 2019. Biopesticides will be evaluated to control S. stelliscabiei.”

Common scab is the most important soil-borne disease of potatoes in Ontario and across Canada. Scab does not reduce yield, but the unsightly pitted lesions render the potatoes unfit for market. To date, management practices to control common scab have proven to be inconsistent across a range of fields. 

As part of the 2018 research funded through the Canadian Agricultural Partnership, 50 soil samples were collected from potato fields in different parts of Ontario. Molecular technology identified four species of bacteria that cause common scab. This technology detected the presence of the toxin thaxthomin which is produced only by pathogenic species of Streptomyces.

In addition, the soil tests showed that there was a correlation between the common scab bacteria present and nutrient levels in the field. 

Polymerase chain reaction (PCR) testing by A & L Laboratories found that 48 fields were infested with common scab and two un-infested fields, one near Alliston and another near Sudbury. Most of the infested fields had multiple species. Streptomyces stelliscabiei was the most common species found followed by S. scabiei, S. acidiscabies and S. turgidiscabies.

Banks notes that two fields with high levels of S.stelliscabieiand no other species had about 100 per cent scab incidence in 2018. The levels of micro- and macro-nutrients varied enormously. Soil pH, per cent base saturation of hydrogen and the K/Mg ratio were found to be the most important factors predicting levels of common scab in Ontario potato fields. 

According to Kevin Brubacher, general manager of the Ontario Potato Board, these findings will help to develop a strategy to reduce the incidence of the disease. The second year of research will be completed in 2019. Biopesticides will be evaluated to control S. stelliscabiei.

Source:  Advancing the Control of Potato Common Scab with Molecular Technology research poster.