INTERSPECIFIC TRANSMISSION OF A HYPOVIRULENCE-ASSOCIATED DOUBLE-STRANDED RNA FROM SCLEROTINIA SCLEROTIORUM TO S. MINORBY HYPHAL ANASTOMOSIS
INTERSPECIFIC TRANSMISSION OF A HYPOVIRULENCE ASSOCIATED DOUBLE-STRANDED RNA FROM SCLEROTINIA SCLEROTIORUM TO S. MINOR BY HYPHAL ANASTOMOSIS
MS MELZER, SS IKEDA and GJ BOLAND
Environmental Biology, University of Guelph,Guelph,Ontario,Canada N1G2W1
Background and objectives
Transmissible hypoviruience has been reported in Sclerotinia sclerotiorum (isolate Ss275) where hypovirulence and atypical colony morphology were associated with a double-stranded RNA (dsRNA) . The hypovirulent phenotype was transmissible between vegetatively-compatible isolates of the species, and recipient isolates developed the hypovirulent phenotype. Hypovirulence has been associated with dsRNA in other pathogenic fungi, particularly Cryphonectria parasitica, where at least three hypovirulence-associated dsRNAs have been classified in the new virus family, Hypoviridae. DSRNA from isolate Ss275 of Sclerotinia sclerotiorum has not been critically characterized but may also belong to this family of viruses. Hypovirulence in C. parasitica has contributed significantly to the control of chestnut blight in Europe and the potential for using hypovirulent isolates of other fungal plant pathogens for biological control of selected diseases has been suggested. However, hypovirulence-associated dsRNAs have not been identified in many pathogens, and the efficacy of individual dsRNAs varies. Fungal viruses and dsRNAs are not transmitted extracellularly and, therefore, transmission between isolates occurs only during hyphal anastomosis. Therefore, promising dsRNAs for biocontrol within one pathogen have limited application to other pathogens. Chen et al.  successfully infected C. parasitica and several closely related fungal species with synthetic transcripts of hypovirus CHV1-EP713 from C. parasitica but, to our knowledge, there are no reports of transmission of dsRNA between fungal species through hyphal anastomosis. The objective of this study was to attempt interspecific transmission of hypovirulence-associated dsRNA by hyphal anastomosis between hypovirulent isolate Ss275 of S. sclerotiorum  and virulent isolates of S. minor.
Results and conclusions
Transmission of the hypovirulent phenotype and dsRNA from isolate Ss275 of S. sclerotiorum to five isolates of S. minor was attempted. Although many S. minor colonies developed atypical colony morphologies when paired with Ss275, the majority of these colonies regained normal morphology after subculture. However, in 9 of 39 aftempts, isolate Sml0 of
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