Australian grain growers are advised to choose barley varieties and fungicide treatment programs carefully following the discovery of a net blotch hybrid that is highly resistant to some Group 3 (azole or demethylase inhibitor) fungicides.
The 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), in collaboration with plant pathologists from the Department of Primary Industries and Regional Development (DPIRD), and the Centre for Crop Health (CCH) at the University of Southern Queensland.
CCDM Fungicide Resistance Management and Disease Impacts Theme leader Fran Lopez-Ruiz said not only had they discovered a fungicide resistant hybrid of the two common barley diseases spot form net blotch (SFNB) and net form net blotch (NFNB), the hybrid was also a clone.
“We’ve known for a couple of years that hybrids of NFNB and SFNB exist in nature,” Dr Lopez-Ruiz said.
“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.
“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.”
In 2017, DPIRD alerted CCDM of fungicide failure in a paddock that had been treated multiple times with formulations containing Group 3 fungicides and was thought to be infected by SFNB. The department sent leaf samples to the CCDM and fungicide resistance tests were carried out, with the hybrid first detected from these samples.
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 350km apart.
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.
CCDM director, Professor Mark Gibberd, said net blotch resistance was a focus of the Centre’s research and this was another important discovery that would better inform growers and agronomists about treatment and management.
“By CCDM, DPIRD and CCH working together on these samples we’re able to build a much clearer picture of the spread and impact of net blotch across Western Australia, building on a range of projects our fungicide resistance experts are working on that have in-field impact.” Professor Gibberd said.
Dr Lopez-Ruiz said growers in affected regions should 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. 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,” he said.
“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.”
Dr Lopez-Ruiz said tebuconazole and propiconazole were among the Group 3 compounds most compromised by these mutations. Therefore, 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, as this would place extra pressure on the other mixing partner. The efficacies of epoxiconazole and prothioconazole were less affected.
“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.
Dr Lopez-Ruiz will discuss the net blotch hybrid finding during his presentation on Day 2 of the GRDC Grains Research Update, Perth, on February 24 and 25. For details about this event, visit the GRDC Updates and events page.