CropWorld 2010: Second mechanism could explain septoria triazole insensitivity

Further research into how Septoria tritici becomes less sensitive to triazole fungicides suggests a second mechanism that transports the fungicide out of the fungus could play a role, Gerd Stammler of BASF said.

The fungus uses efflux pumps to fight off the natural defences from the plant by pumping out the toxins the plant uses to fight infection back into the plant. Those pumps can also remove fungicide, particularly if the fungus evolves so it has more pumps than normal.

In agar plate resistance tests conducted at Rothamsted Research, adding an inhibitor that stopped those pumps from working reduced the amount of fungicide required to kill the fungus, he said. "It suggests efflux pumps could be playing a role in reduced sensitivity to triazole."

The research could also help explain why laboratory tests didnt correlate particularly well with resistance in the field, Bill Clark, director of Brooms Barn, told Farmers Weekly.
 
In the agar plate tests the fungus didnt have to use the pumps to fight the toxins naturally produced by plants to fight infections, and could therefore utilise the pumps to remove fungicide, he explained.

That could lead to high concentrations of fungicide being required to kill the fungus in the plate. "But instead of accepting that as a highly resistant strain, the Rothamsted team has added an inhibitor, and shown that you get control with more normal fungicide concentrations."