Ismail Ismail,* Lincoln Harper, Steven Van Den Heuvel, Anthony Borneman, Fran Lopez Ruiz, and Mark Sosnowski
*SARDI, SARDI, Plant Research Centre, Gate 2A, Hartley Grove, Urrbrae, South Australia 5064, Australia (Ismail.Ismail@sa.gov.au)

Grapevine powdery mildew (Erysiphe necator) and downy mildew (Plasmopara viticola) are significant diseases in Australia and worldwide. Fungicides are the key to managing these diseases. However, frequent use can lead to fungicide resistance. Samples were collected from five states in Australia from 2017 to 2023 and phenotyping and genotyping were used to investigate resistance status. Phenotyping was conducted for six and four fungicide groups for powdery and downy mildew, respectively. Both pathogens had varying levels of reduced sensitivity to most fungicide groups tested, with resistance confirmed for fungicides from quinone outside inhibitors (QoI, group 11) and proquinazid (group 13) for E. necator and phenylamide (group 4) and QoI for P. viticola. Two mutations, G143A and Y136F, were identified in E. necator populations. There were strong relationships between reduced sensitivity to QoIs and the presence of the G143A mutation in the CYTB gene, but not between reduced sensitivity to demethylation inhibitor (DMI) and Y136F mutation in the CYP51 gene. The mutant H242R/Y, associated with resistance to succinate dehydrogenase inhibitors (SDHI, group 7), was not detected, but reduced sensitivity was recorded for this group. G143A was also detected in P. viticola isolates, with a strong relationship between phenotype and genotype for QoI. Techniques are being improved to increase the monitoring capacity for fungicide resistance using rotorod spore traps and other sample collection methods to detect mutations linked with resistance. High-throughput laboratory and in-field qPCR methods are being developed and validated, with high-throughput sequencing to evaluate their capability to rapidly and cost-effectively identify fungicide resistance mutants.

Funding Support: Wine Australia and CRC-SAAFE