Ground Cover Supplement : GC Supplement - Cereal foliar fungal diseases
21 Western region MODEL EXPOSES MILDEW WEAKNESS Years of fundamental research have resulted in Western australian barley growers now being able to choose with confidence the most effective fungicide for resistant powdery mildew By Janet Paterson CLEVER SCIENTIFIC DETECTIVE work has unravelled why some fungicides still work against barley powdery mildew despite the resistant mutants having apparently spread through most of the barley-growing areas in Western Australia. The research, which forms part of Curtin University scientist Madeline Tucker's PhD work, has resulted in a simple diagnostic tool that identifies the fungicide compounds that will still work against specific mutant strains of the powdery mildew fungus. Importantly, one of the goals of the project is to deliver predictions on the likely evolution of powdery mildew mutants in WA and how these will affect the efficacy of specific fungicide compounds. The work could help to slow the spread of powdery mildew fungicide resistance in barley and prolong the useful life of the remaining chemicals still effective against the disease. The road to these exciting findings has been long -- requiring the development of several novel laboratory techniques to enable quick identification and safe storage of the powdery mildew pathogen and development of an innovative model to monitor the many subtle mutations of the costly disease. Australian Centre for Necrotrophic Fungal Pathogens (ACNFP) scientist Dr Fran Lopez, who works with Ms Tucker at Curtin University, says the research was triggered by the discovery that the barley powdery mildew pathogen in WA had more and different mutations than European powdery mildew mutants. "We wanted to know how these extra mutations were contributing to the pattern of fungicide resistance we had identified in WA," Dr Lopez says. RESISTANCE SURVEY A survey across the barley-growing areas of WA and sites in the eastern states of Australia resulted in the collection of 143 isolates of barley powdery mildew. Each of these isolates was then tested against the fungicide compounds used in WA to determine which isolates were resistant to which compounds and the compounds that remained effective against the disease. Ms Tucker then sequenced the fungicide target gene of the powdery mildew pathogen to determine how the gene sequences correlated with the observed resistance patterns across WA. The results of the genetic sequencing work were taken to the UK, where Ms Tucker worked with researchers at the Rothamsted Research station to determine the contribution of each mutation to the observed fungicide resistance. MODELS Subsequent specialised modelling work characterised the structural interactions between the genetic mutations and the fungicides in the fungicide-binding site. "What she found was very exciting," Dr Lopez says. "The model showed that each mutant had a slightly changed target site for the fungicide so that some of the fungicides could still engage with PHOTO: NICOLE BAXTER “We can now receive an infected barley leaf from a grower who has experienced fungicide failure against powdery mildew and test the sample for the fungicide compounds against which it is still sensitive.” -- DR FRAN LOPEZ and kill the fungus but others could no longer connect to the fungus to cause it damage even though they were a very similar chemical compound." The results explain the on-ground experience of barley growers in WA, who have found that the same fungicide rendered ineffective in one barley region is still effective in another -- despite both regions having the resistant pathogen. "We can now receive an infected barley leaf from a grower who has experienced fungicide failure against powdery mildew and test the sample for the fungicide compounds against which it is still sensitive," Dr Lopez says. The research results mean growers can now choose an effective fungicide option against the mildew pathogen type in their area, which will help to reduce the amount of pathogen and the chance of new mutations occurring. □ grdc research code cur00017 more information: Professor Richard Oliver, ACNFP, 08 9266 9266, email@example.com PhD student Madeline Tucker checks her barley powdery mildew experiments at Curtin University in WA.
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