Scientists identify resistance mechanism in phoma stem canker

A major crop disease may become harder to control because fungal pathogens are less susceptible to widely used fungicides.

Genetic changes in fungal pathogen populations are reducing the effectiveness of azole fungicides – used by farmers for decades when tackling phoma stem canker, say scientists at Rothamsted Research.

Research published in the journal Pest Management Science, confirms that scientists have found decreased azole sensitivity for the first time worldwide in Phoma pathogen Plenodomus biglobosus.

Reduced sensitivity in western European populations of P. lingam to azole fungicides was first reported last year. Taken together, the findings raise pressing questions about the sustainability of current disease management strategies.

Unlike in P. lingam, the azole sensitivity shifts in P. biglobosus were linked to a single mutation within the CYP51 (the target of azole fungicides) gene. This represents the first report of target site resistance to azole fungicides in a Phoma pathogen.

“The mutation found in P. biglobosus is linked to a 7-fold decrease in sensitivity to the azoles tested. On its own, this is unlikely to contribute to Phoma disease control failure, but it is a worrying step in the wrong direction” said research leader Kevin King.

“Ongoing evolution of the pathogens may in future lead to azole resistance in the field and subsequent disease control failures.”

As oilseed rape remains a vital crop for food and biofuel production in the UK and beyond, the emergence of such fungicide resistance could have serious food and energy security implications.

To date the new mutation has been confirmed in Polish and UK populations of P. biglobosus, and could, in part, help explain recent findings of the strain becoming an increasingly important Phoma stem canker pathogen in Europe.

Distribution

Further surveys are now required to monitor the distribution and extent of the new mutation in European P. biglobosus populations and whether such mutations may also now be emerging in P. lingam.

Additional research is also needed into strategies to slow selection for resistance caused by extensive use of azoles.

“Research into integrated pest management strategies — including crop rotation, resistant cultivars, and reduced reliance on fungicides — will also be important to safeguard future yields,” said report co-author Jon West.

The work was a collaborative project between Rothamsted Research and the Polish Institute of Genetics. Work at Rothamsted was supported by the Growing Health and Resilient Farming Futures Institute Strategic Programmes.