A high-tech, two-pronged approach has been taken to generate field profiles of fungicide resistance in the foliar net blotch diseases of barley across regions of Western Australia. The aim of the study being to determine the frequency of fungicide resistance in fields.
“We know that there is a mix of fungicide resistant types of the net blotch fungi across the WA cropping region but now we need to quantify it to better inform management interventions,” says Dr Noel Knight who is leading the research at the Centre for Crop and Disease Management at Curtin University.
Control of both the spot form (Pyrenophora teres f. maculata) and net form (P. teres f. teres) of net blotch diseases relies on three major classes of fungicides; demethylation inhibitor (DMI, FRAC Group 3), succinate dehydrogenase inhibitor (SDHI, FRAC Group 7) and quinone outside inhibitors (QoI, FRAC Group 11).
However, resistance and reduced sensitivity to both DMI and SDHI fungicides in net blotch pathogens are increasing. Resistance to QoI fungicides, at present, is not an issue for net blotch but it is for powdery mildew, so a considered approach needs to be taken to its use.
Samples were collected from twenty barley fields in September, 2021 in the low-medium rainfall zone of WA.
“To determine the fungicide resistance frequency and diversity we used phenotyping and genotyping workflows.”
“The combined approach gives us a visual assessment of the fungicide effect on living fungi, and information on the presence of mutations unique to resistance or reduced sensitivity to fungicides.”
“Genetic diagnostics relies on continually monitoring net blotch samples across regions for fungicide resistance and confirming which genetic changes are emerging in fields. Diagnostic tests have been designed for more than 15 unique mutations, however as new resistance types are discovered, more tests must be designed.”
“Our latest genotyping approach, which used a technique called digital PCR, allowed a snapshot of fungicide resistance in a field to be generated from combined disease lesions. This bypassed the process of growing fungi for phenotyping and gave new insight into the frequencies of resistant types.”
Results showed resistance and reduced sensitivity in net blotch to DMI fungicides is widespread across the low-medium rainfall zone, whilst for SDHIs it appears to be regionally isolated.
The genotype frequencies for both resistance and reduced sensitivity across the 20 fields are shown in Figure 1, indicating that resistance or reduced sensitivity to both fungicides is present in nearly every field.
Figure 1: Genotype frequencies of net blotch fungi with resistance and reduced sensitivity to demethylation inhibitor (DMI) and succinate dehydrogenase inhibitor fungicides (SDHI) across 20 fields in WA.
Source: CCDM
“We are not sure, as yet, what threshold is significant to warrant concern for disease control. However, we do know the risk of fungicide resistance emerging is enhanced by growing barley on barley and applying the same fungicides each season.”
“Summaries of fungicide resistance frequencies and generalised risk levels were provided to all the growers involved and initial feedback has indicated that growers are implementing changes in field management, including crop rotations and improved stubble reduction,” Dr Knight says.
At the moment the best practice is to use fungicides as part of an integrated disease management plan and to ensure modes of action are rotated or mixed.
Dr Knight says the research emphasised the importance of growers needing to know their fields.
“Together with understanding soil types, optimal crops and soil moisture, growers should also have a good idea of disease profile and possible fungicide resistance.”
More information: Dr Noel Knight, noel.knight@curtin.edu.au
Read more: Field profiling for netblotch fingicide resistance in low-medium rainfall zone. 2022 GRDC Update