Temperature and structural effects on transfer of double-stranded RNA among isolates of the chestnut blight fungus (Cryphonectria parasitica).

Cryphonectria parasitica is a unique fungus which can serve as a model for understanding transfer of genes between eukaryotic microorganisms. We studied transfer of double-stranded RNA (dsRNA) between compatible and incompatible strains of C. parasitica to determine whether hyphal types or temperature could restrict that exchange. Hyphal connections between incompatible strains occurred at about 30% of the frequency of connections between compatible strains and differed morphologically. Gel electrophoresis and in situ hybridization confirmed that dsRNA was transferred through substrate hyphae but not through aerial hyphae. Freezing temperatures resulted in the loss of dsRNA from the new mycelium of the donor colony and stimulated the production of virulent pycnidiospores. These temperature and structural restrictions may help to explain the lack of spread of the dsRNA despite its presence in the field.