Phenotypic changes associated with wild-type and mutant hypovirus RNA transfection of plant pathogenic fungi phylogenetically related to Cryphonectria parasitica

Double-stranded RNA viruses within the genus Hypovirus attenuate virulence of the chestnut blight fungus Cryphonectria parasitica. The recent development of an infectious synthetic hypovirus transcript has allowed the expansion of hypovirus infection and virus-mediated virulence attenuation to several fungal species not previously shown to harbor hypoviruses. This report compared the phenotypic changes resulting from transfection-mediated hypovirus infection of Cryphonectria parasitica, C. radicalis, C. havanensis, C. cubensis, and Endothia gyrosa. By comparing virus-mediated phenotypic changes in different fungal hosts transfected with wild-type and mutated viral transcripts, it was possible to examine the relative contribution of viral and host genetic backgrounds for some traits. For example, hypovirus infection reduced sporulation in all fungal hosts, while it suppressed pigmentation in some species and induced pigment production in others. The hypovirus-encoded protein p29 was found to have a significant impact on both sporulation and pigmentation in different fungal hosts. All fungal species tested were able to transmit virus by anastomosis within the same species. However, considerable differences were observed in the efficiency with which different fungal species transmitted hypoviruses through conidia. A molecular phylogenetic analysis based on nuclear ribosomal DNA nucleotide sequences revealed the five fungal species to be closely related. Possible relationships between taxonomic position and hypovirus host range were discussed. The ability to introduce hypoviruses into different fungal species holds promise for the expanded utility of virus-mediated hypovirulence for understanding and controlling fungal pathogenicity.