With 95% of UK P. biglobosus isolates resistant to two SDHI fungicides in laboratory tests, the discovery puts renewed focus on genetics, surveillance and fungicide stewardship working together to protect oilseed rape yields.
Scientists have confirmed the world’s first cases of resistance to SDHI fungicides in Plenodomus biglobosus, one of two fungal pathogens responsible for Phoma stem canker in oilseed rape.
The discovery raises concerns about future control of the disease, which can cause substantial yield losses. While the related pathogen Plenodomus lingam has historically attracted more attention, P. biglobosus has become increasingly important in UK and European crops.
Resistance Widespread in UK Samples
In a study published in Pest Management Science, Rothamsted Research scientists screened P. biglobosus populations collected from the UK and Poland. They found that 95% of UK isolates were resistant to the SDHI (succinate dehydrogenase inhibitor) fungicides boscalid and fluxapyroxad, compared with 6% of Polish isolates.
Some UK isolates showed up to a 500-fold reduction in sensitivity under laboratory conditions. Resistance was linked to mutations in genes encoding the fungal succinate dehydrogenase enzyme, which SDHI fungicides target, according to a press release.
The researchers found little evidence that these mutations reduced the pathogen’s fitness, suggesting resistant strains could persist in field populations.
“The scale of resistance we detected in UK populations was striking,” said Dr Kevin King, who led the research at Rothamsted. “This is the first confirmed report of SDHI resistance in P. biglobosus anywhere in the world. Further research is now needed to determine what impact this may have on phoma disease control under field conditions.”
Monitoring Emerging Threats
The findings follow recent Rothamsted reports of reduced sensitivity to azole fungicides in European populations of both Phoma stem canker pathogens. Together, the studies highlight the importance of resistance monitoring and integrated disease management.
“This work highlights the importance of ongoing surveillance,” said Professor Jon West, co-author of the study. “SDHI-resistant P. lingam has recently been detected in Australia but not yet in Europe. Monitoring both Phoma pathogens will provide early warning of emerging resistance threats and help protect the long-term effectiveness of fungicides.”
