ABSTRACT
Two types of association between fungi and viruses can be distinguished. First, fungi can act as vectors for the transmission of a number of soil-borne plant viruses. Association between virus and vector is generally specific and such viruses can be canied either externally or internally by the fungus.' There is, however, no evidence that these viruses replicate in the fungus and they are properly classified as plant viruses. Second, fungi can be hosts to viruses which replicate, sometimes to high titers, within the fungal cells. These are the fungal viruses (mycoviruses) with which the present chapter is concerned.
