IN AN ominous sign for barley producers in regions with high risk of fungal disease, authorities have confirmed the discovery of a new hybrid strain of net blotch resistant to one of the key fungicide modes of action.
The net blotch, discovered in the Esperance and South Stirling regions of far southern Western Australia, is a hybrid of both the spot and net forms of net blotch (SFNB and NFNB) and is highly resistant to some Group 3 (azole or demethylase inhibitor) fungicides.
Within that, tebuconazole and propiconazole were among the Group 3 compounds most compromised by these mutations while the efficacies of epoxiconazole and prothioconazole were less affected.
The alarming discovery was made by researchers from the Centre for Crop and Disease Management (CCDM), a national research centre co-supported by Curtin University and the Grains Research and Development Corporation (GRDC).
CCDM fungicide resistance management leader Fran Lopez-Ruiz said growers needed to carefully consider their variety choices and their fungicide strategies to try and keep the problem in check.
"We know the hybrid is quite virulent on (the variety) Oxford, as most of the hybrid clones we have collected so far have come from infected Oxford samples," Dr Lopez-Ruiz said.
"We're looking into Planet and La Trobe too, as these are the only two other varieties where we have found these highly resistant strains, albeit at far lower frequencies," he said.
He said researchers had known for a while a hybrid of SFNB and NFNB existed but added they had just discovered the multiple genetic mutations within the strain.
And its make-up will mean the new hybrid is especially difficult to get on top of.
"The hybrids are genetically identical - they're clones, which means they are reproducing asexually across the Esperance and South Stirling regions."
The clones have detected in locations up to 350km apart and are notable for the virulence of their fungicide resistance.
According to CCDM researcher Wesley Mair, 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 now convinced we have discovered a highly resistant hybrid," Mr Mair said.
Dr Lopez-Perez said farmers needed to mix their fungicide rotations up, keeping an eye on the efficacy of all products, not just the azoles.
"Other fungicide modes of action, such as those from Group 11 (QoIs) and Group 7 (SDHIs), should be in the mix too, as they remain effective at controlling these hybrids," he said.
"However, the use of SDHI fungicides should be monitored carefully given the recent discovery of SDHI resistance in NFNB in South Australia," he said.