A FUNGICIDE resistant hybrid of two common barley diseases, spot form net blotch (SFNB) and net form net blotch (NFNB), has been discovered in Western Australia by the Centre for Crop and Disease Management (CCDM).
CCDM researchers discovered the hybrid after conducting tests on leaf samples collected from a farm a couple of years ago, with the team eventually finding the net blotch hybrid was highly resistant to some Group 3 (azole or demethylase inhibitor) fungicides.
CCDM fungicide resistance management and disease impacts team leader Fran Lopez-Ruiz said they've known for a couple of years that hybrids of NFNB and SFNB existed in nature.
"But now, not only do we know they exist, we also know they exist with multiple genetic mutations that make them highly resistant to some Group 3 fungicides," Dr Lopez-Ruiz said.
"On top of this, they're also genetically identical - they're clones, which means they are reproducing asexually across the Esperance and South Stirling regions."
CCDM was alerted of fungicide failure in a paddock that had been treated multiple times with formulations containing Group 3 fungicides in 2017, with the hybrid first detected from samples taken.
Further samples were then tested from an additional seven sites across the South Stirling, Frankland, Amelup and Esperance regions, with hybrid clones detected up to 350 kilometres apart.
CCDM researcher Wesley Mair said tests found strains of the pathogen that were not only resistant to some Group 3 fungicides, but far more resistant than any NFNB or SFNB strain the team had ever studied.
"From further genetic analysis we saw that this type of net blotch carried known mutations for fungicide resistance in NFNB and known mutations for fungicide resistance in SFNB and after further tests we are convinced we have discovered a highly resistant hybrid," Mr Mair said.
Dr Lopez-Ruiz said Australian growers should choose fungicide treatment programs carefully and advised growers in affected regions to continue with their robust integrated disease management strategies, particularly when it came to choosing varieties.
"We know the hybrid is quite virulent on Oxford, as most of the hybrid clones we have collected so far have come from infected Oxford samples," Mr Lopez-Ruiz said.
"We're looking into Planet (PBR) and La Trobe (PBR) too, as these are the only two other varieties where we have found these highly resistant strains, albeit at far lower frequencies.
"With improved knowledge of host sensitivity, it may be possible for growers to select varieties of low sensitivity, which could lead to a reduction in the population of the hybrid and slow its spread, however, we can't rule out the possibility that it can adapt, so we need to keep tabs on it."
According to CCDM, tebuconazole and propiconazole were among the Group 3 compounds most compromised by these mutations, meaning their use should be avoided in solo formulations and limited when any of these two compounds were mixed with a different fungicide, especially from Group 3.
The efficacies of epoxiconazole and prothioconazole were less affected.
More information on the net blotch hybrid will be provided by Dr Lopez-Ruiz during his presentation at the GRDC Grains Research Update in Perth next week.
