RNA interference (RNAi) is a natural defence mechanism found in most eukaryotes. It protects them against double-stranded RNA (dsRNA) viruses and has several other functions.
Sclerotinia stem rot is a disease that can cause significant yield losses in canola. It is caused by the fungus Sclerotinia sclerotiorum. We aimed to test whether we could protect canola against this pathogen by means of RNAi.
The method we chose was to spray canola with dsRNA targeting fungal genes believed to be either essential for life or pathogenesis. We hypothesised that this would be taken up by the invading fungus and treated like foreign viral dsRNA. The fungus would then invoke its RNAi machinery to degrade mRNA transcripts matching the dsRNA sequence. By designing the dsRNA to have one strand complementary to one or more essential fungal transcripts, we hypothesised that we could induce S. sclerotiorum into destroying its own mRNA, killing the fungus or reducing its pathogenicity.
This approach promised several benefits over the application of chemical fungicides: off-target effects are minimised by careful construct design, and the dsRNA breaks down in the environment, leaving behind no toxic residue.
Our initial tasks were to develop robust assays for evaluating different dsRNA constructs. We have also been working on studying transport of dsRNA through the plant after the leaf canopy is sprayed.
An overview of our results will be presented; they lead us to conclude that dsRNA delivered via spraying crop plants is not a feasible method of controlling this necrotrophic pathogen.