CCDM scientists have, for the first time, characterised a mutation associated with reduced sensitivity to succinate dehydrogenase inhibitor (SDHI; Group 7) fungicides in barley loose smut.
Author: Charlotte Italiano, 21 September 2026, Source: CCDM
Fungicides are important tools for Australian growers in managing fungal diseases—but what happens when they become less effective, or stop working altogether?
Scientists from the Centre for Crop and Disease Management (CCDM) have, for the first time, characterised a mutation associated with reduced sensitivity to succinate dehydrogenase inhibitor (SDHI; Group 7) fungicides in barley loose smut. These fungicides include fluxapyroxad, carboxin and penflufen. The discovery followed analysis of samples collected between 2024 and 2025 across New South Wales, Queensland and Western Australia.
This mutation is novel, marking the first time this specific genetic change linked to reduced SDHI sensitivity has been identified in loose smut anywhere in the world.
However, it is important to emphasise that this does not indicate widespread field failure.
CCDM Associate Professor Fran Lopez‑Ruiz said the findings were consistent with field observations, where growers had reported unexpected levels of disease despite fungicide treatment.
“For us, it’s very important to detect and characterise resistance when it’s at a low frequency, as it means there is still time for industry to respond and put the right management strategies in place before resistance becomes widespread,” Fran said.
Detecting reduced fungicide sensitivity
Loose smut is a seed‑borne disease of barley that infects grain heads with dark, powdery spores. Because the pathogen is carried inside the seed, using seed from infected paddocks allows the disease to be carried directly into the next crop. High humidity during flowering and wet seasonal conditions favours disease development.
Barley samples submitted during the 2024 season from across NSW and Qld first indicated reduced sensitivity to SDHI fungicides. Follow-up analysis of 2025 samples from Wagga Wagga (NSW), Crossman and Gibson (WA), and Toowoomba and Warwick (Qld) confirmed high levels of this mutation.
How the mutation was found
How did CCDM Research Assistant Steven Chang test the pathogen samples? He started by growing them on plates and applying small amounts of SDHI (Group 7) fungicides.
“When the fungicide is working, the pathogen should stop growing,” Steven said. “If it keeps growing, it suggests it may be becoming less sensitive, so we then measure how strong that growth is.”
Samples that continued to grow at higher fungicide levels were examined further. Steven analysed their DNA to identify any underlying genetic changes. Using a sequencing pipeline developed at CCDM, the team was able to examine the entire target gene rather than just small sections, providing a clearer picture of genetic variation and enabling the detection of mutations that may be missed by traditional methods alone.
The improved technique has made testing more effective. When the team retested barley samples infected with loose smut from 2021, collected in Qld, they identified the same mutation, confirming its persistence over time.
“Normally, the fungicide binds to an essential enzyme in the pathogen and stops it from surviving,” Steven explained. “But when that structure changes due to a mutation, the fungicide can’t bind properly – like a key that no longer fits the lock.”
What this means for growers and advisers
Although SDHI fungicides have shown reduced sensitivity, plant pathologist Brad Baxter said the field impact of this mutation has not yet been quantified, but growers still have effective tools available.
“Reduced sensitivity means SDHI-based seed treatments should not be relied on as the sole control measure and should instead be used as part of an integrated disease management strategy,” he said.
He recommends growers:
- Source clean seed when infection levels in harvested seed are expected to be high. As a guide, 1% – 5% loose smut infection level at heading (GS59), use a registered fungicide seed treatment the following season. Where incidence exceeds 5% infection, source new seed lot.
- Research conducted by Andrea Hills (WA DPIRD) indicates that seed grading may reduce infection levels by removing the smallest seed fractions but not eliminate all infected seed.
- Consider varietal susceptibility if reliable information is available and avoid varieties or seed lots with regular high levels of in-crop disease.
- Ensure uniform application of the fungicide seed dressing by using consistently sized, graded seed, the correct water and fungicide rates to avoid under- or overdosing, and an appropriate application speed.
- Alternate effective fungicide groups between seasons and use registered mixtures, containing more than one effective mode of action if possible. Always adhere to label rates and instructions.
“This is an early warning sign. Acting now with an integrated approach will help protect fungicides and keep them working into the future,” Brad said.
Ongoing research, surveillance and access to up-to-date information remain critical for managing fungicide resistance.
The Australian grains fungicide resistance landscape
The recent detection of reduced sensitivity to SDHI fungicides in barley loose smut represents a new addition to Australia’s growing fungicide resistance profile. This finding will be incorporated into CCDM’s national fungicide resistance map, which tracks resistance across key grain diseases and regions (see below).
Fungicides are grouped according to their biochemical mode of action (MoA). However, only a small proportion of these are registered for use in Australia, increasing the risk of resistance developing as growers rely on a limited number of options.
The resistance map already highlights established and emerging cases across multiple crop diseases, showing how resistance can develop over time and across different fungicide groups. Compared to earlier versions of the map, the inclusion of loose smut reflects a growing list of pathogens showing reduced sensitivity.
Importantly, these new detections are being driven by improved screening pipelines, which are enabling researchers to identify resistance mutations earlier and more accurately in field populations. This capability is helping to build a clearer picture of how resistance is emerging and spreading across the Australian grains industry.
If you suspect resistance in your paddock, contact the CCDM Fungicide Resistance Research Group at frg@curtin.edu.au.
For more information on fungicide resistance management, visit the Grower advice page on the Disease Management Extension Network (formerly AFREN) website: https://afren.com.au/understanding/#grower-advice.
Acknowledgements
- NSW samples of barley loose smut were submitted by Brad Baxter and Steven Simpendorfer from NSW Department of Primary Industries and Regional Development (NSW DPIRD). These samples where submitted or collected under GRDC and NSW DPIRD co-funded project. They thank growers and agronomist for their assistance.
- Qld 2024 samples were submitted by Grace Fowler from MCA Ag.
- Qld 2025 and 2021 samples were submitted by Professor Levente Kiss and Associate Professor Anke Martin (University of Southern Queensland) and Dr Lisle Snyman (Queensland Department of Primary Industries). These samples came from a project supported by the Broadacre Cropping Initiative.
- WA samples were submitted by Andrea Hills from Western Australian Department of Primary Industries and Regional Development (WA DPIRD) and Giles McMeiken (Farmanco). This season, WA DPIRD are running a series of trials addressing issues around management of loose smut, including one testing whether the new SDHI mutation will have field level effects on loose smut control using seed dressings.