Understanding the basis of agrochemical resistance in biotrophic grapevine pathogens
The development of resistance to agrochemicals is an ever-increasing problem in agriculture, and one for which the Australian wine sector is not immune. Results of arecent SARDI/AWRI research project have shown that there is widespread prevalence of known resistance alleles to many of the commonly used agrochemicals in the main biotrophic grapevine pathogens Erysiphe necator (powdery mildew) and Plasmopara viticola (downy mildew). Firstly, this project continues current collaborative work with SARDI (under the SARDI-led project SAR1602), where the AWRI is providing the key genotype information to accompany the SARDI phenotypic deliverables. Secondly, the AWRI-focused component will look to extend the previously developed technology developed beyond mapping individual resistance alleles, to the use of whole genome sequencing to simultaneously assess all known resistant loci, in addition to providing population data regarding the evolution of these traits in the field.
While the molecular basis of resistance is well known for many agrochemicals, there remain agrochemicals for which targets are not known. There are key agrochemicals, such as metalaxyl (the key control measure for downy mildew) for which field resistance is readily observed but the genetic cause (and therefore a genetic test for resistance) is unavailable. The AWRI-led portion of this project therefore also aims to use genome sequencing technology to determine the genetic basis for resistance of Plasmopara viticola (downy mildew) to metalaxyl, providing the means to design a simple genetic test for the presence of field resistance. Here, the AWRI will be responsible for isolating, and obtaining genomic DNA from phenotyped downy mildew isolates so that whole genome sequencing and assembly may be performed. Finally, genome sequencing approaches and metagenomics will be explored for subsequent population analysis of trunk disease isolates, in collaboration with the SARDI-led project, ‘Grapevine trunk disease management for vineyard longevity in diverse climates in Australia’.
Improving the understanding of agrochemical resistance in powdery mildew
Previous research showed that known resistance mutations to many commonly used agrochemicals are prevalent in both powdery and downy mildew. However, it is not yet fully understood how the presence of the mutations relates to loss of field efficacy for key agrochemicals. This is an important question to be answered before genetic tests can be used to inform viticultural practices. The AWRI is working with SARDI to use next-generation sequencing to track the prevalence of resistance alleles in both powdery and downy mildew. During the year, key resistance loci were genotyped across a number of powdery and downy mildew samples.
Techniques were also developed to extract DNA from spore traps, which can be used to monitor the presence of fungi in the vineyard (including pathogens) and to determine the species composition of the spore-trap sample via next-generation sequencing of ‘DNA barcodes’.