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Wheat powdery mildew mutations found in Eastern States

Media release

Researchers of the national Centre for Crop and Disease Management (CCDM) have recently observed the first signs of mutations that could lead to fungicide resistance issues in wheat powdery mildew in Australia.

The CCDM, which is co-funded by Curtin University and the Grains Research and Development Corporation (GRDC), has detected a mutation, Y136F, in wheat powdery mildew isolates from New South Wales and Tasmania that could see a reduction in the control of the disease by triazole fungicides.

Ms Madeline Tucker, of CCDM’s Fungicide Resistance Group, was part of the research team that first discovered barley powdery mildew resistance in Western Australia (WA) in 2009.

Since wheat powdery mildew and barley powdery mildew pathogens are genetically very similar, Ms Tucker said the team have been able to use their knowledge on the development of barley powdery mildew resistance to help growers manage the development of wheat powdery mildew resistance.

“Having looked at the progression of fungicide resistance in the barley powdery mildew population in WA, we now know that it’s the combination of two mutations occurring in the same powdery mildew organism that results in significant resistance effects in the field,” Ms Tucker said.

“The first mutation – referred to as the Y136F mutation – is quite harmless, however we have found it acts as a ‘gateway’ to the second mutation – S509T – which is much more serious.The combination of both mutations presents clear signs of fungicide resistance to tebuconazole, as well as possible control issues with triadimefon and flutriafol.

“We have observed the first mutation (Y136F) in wheat powdery mildew and are concerned that the second mutation (S509T) may now have the gateway it needs to also occur.

“While this recent finding of the Y136F mutation in wheat powdery mildew is not good news, it has been discovered early and this gives growers the chance to act early,” Ms Tucker said.

Ms Tucker explained the only way to slow down the occurrence of resistance mutations in wheat powdery mildew is to decrease selection for those mutations.

“Growers need to continue to be mindful of how they use fungicides and stick to integrated disease management strategies that do not depend solely on fungicides, such as using disease resistant crop varieties, crop rotations, stubble management and green bridge control,” Ms Tucker said.

“Using fungicides with the same mode of action repetitively and planting wheat varieties susceptible to disease is a sure recipe for the build-up of fungicide resistance. Fungicide use does not cause resistance mutations, however its incorrect use can increase selection for resistance mutations.”

CCDM expects this coming season to be another big year for wheat powdery mildew, particularly in WA with so much infected stubble carryover from last year

Growers who suspect disease control issues can contact CCDM’s Fungicide Resistance Group at frg@curtin.edu.au for advice or instructions on sampling.