Oral Presentation Australasian Plant Pathology Society Conference 2025

Fungicide resistance in the air! (118579)

Ismail Ahmed Ismail 1 2 , Lincoln Harper 3 , Fran Lopez 3 , Steven Van Den Heuvel 4 , Anthony Borneman 2 4 , Danièle Giblot-Ducray 1 2 , Mark Sosnowski 1 2
  1. South Australian Research and Development Institute - SARDI, SA, Australia
  2. School of Agriculture, Food and Wine, Waite Research Institute, The University of Adelaide, Urrbrae, Sa, Australia
  3. Centre for Crop and Disease Management, Curtin University, Bentley, WA, Australia
  4. Australian Wine Research Institute, AWRI, Urrbrae, SA, Australia

Powdery mildew (Erysiphe necator) of grapevine is one of the most important diseases in Australia and worldwide. Fungicides are vital tools in controlling this disease, however fungicide resistance is an increasingly problematic issue facing the industry. Previously in Australian vineyards, fungicide resistance has been detected for Quinone outside inhibitors (QoI, FRAC group 11), Demethylation inhibitors (DMI, FRAC group 3) and reduced sensitivity for Succinate dehydrogenase inhibitors (SDHI)(McKay et al., 2021). The resistance to QoIs is associated with the most common single nucleotide polymorphism (SNP) in the mitochondrial cytochrome b gene (cytb), this SNP causing a glycine to alanine substitution at amino acid position 143 (i.e., G143A; (Miles et al., 2021)). The aim of this study was to develop allele-specific TaqMan probes to detect G143A in the cytb protein. A high throughput qPCR (HT-qPCR) assay (Miles et al., 2021) was used to identify G143A in airborne E. necator. To confirm the detection of G143A, high throughput sequencing (HTS;(Sosnowski et al., 2023)) for the cytb gene amplicon amplified by PCR was used, and proportions of resistant and sensitive alleles were determined. HTS was also used to identify the Y136F mutation in the cytochrome P450 eburicol 14α-demethylase (cyp51) gene and the H242x mutation in the sdh gene, associated with resistance for DMIs and SDHIs respectively. National trials using rotorod spore traps were conducted over two seasons (2023-24 and 2024-25) in five Australian states, covering ten major grapevine growing regions. Spore traps were run for 48h every fortnight, samples were collected from bud burst until harvest. HT-qPCR analysis showed that the spore traps were effective at capturing airborne spores, both wildtype and resistant (possessing the G143A mutant). HTS confirmed these results and identified the wildtype and Y136F mutant, the H242x mutant was not detected in any samples. The presence of these mutants fluctuated during the seasons, however G143A was more frequent from mid to the end of the season when disease pressure was high. HT-qPCR proved to be reliable and sensitive in detecting resistance, even before symptoms were observed in vineyards. Coupling rotorod spore trap and HT-qPCR could improve fungicide resistance monitoring and can be used as a guide to modify future spray programs. Continued monitoring is crucial to managing and minimising fungicide resistance in Australia, and future research aims to add more resistance markers for HT-qPCR testing.

 

  1. Mckay S, Ismail I, Harper L, Lopez F, Van Den Heuvel S, Borneman A, Hall B, Sosnowski M, 2021. Fungicide resistance status of powdery and downy mildew in Australia. Wine and Viticulture Journal 36, 54-61. Miles TD, Neill T, Colle M, Warneke B, Robinson G, Stergiopoulos I, Mahaffee WF, 2021. Allele-specific detection methods for QoI fungicide resistant Erysiphe necator in vineyards. Plant Dis 105, 175-82. Sosnowski M, Mckay S, Ismail I, Lopez-Ruiz F, Harper L, Herderich M, Borneman A, 2023. Improving the understanding of fungicide resistance in Australian viticulture.Final Report to Wine Australia, Project SAR1701-1.2, March 2023.