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 and many other crops. It is caused by the fungus Sclerotinia sclerotiorum. Ascochyta lentis and Ascochyta rabiei cause Ascochyta blight of lentil and chickpea respectively. We aimed to test whether we could protect plants against these pathogens by means of RNAi.
The method we chose was to spray plants with dsRNA which targets 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. This would lead to death or loss of pathogenicity in the fungus.
This approach promises 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.
We tested various dsRNA constructs in vitro and in planta, but without success, even when trying to replace positive results in the literature.
To investigate why dsRNA was failing to have an impact on these fungal species, we are using a recently developed technique to isolate and sequence small interfering RNAs (siRNA). This will allow us to determine whether the dsRNA we apply is being processed by the RNAi machinery of the fungus. Without this processing, it is not possible for the application of dsRNA to have any negative effect on the pathogen.