Defective Strains and Phenotypic Mixing

This communication discusses recent work on phenotypic mixing with various viruses and describes relevant results with pm 2 strain of tobacco mosaic virus (TMV) and another defective strain which we have recently isolated. The term ‘phenotypic mixing’ is used here to mean the coating of the nucleic acid of one virus or virus strain with the protein of another.

The defective turin strain of TMV was isolated from a pepper plant growing in an experimental plot at the University of Turin and we shall call it the ‘turin’ strain. The pepper plant was also infected with cucumber mosaic virus and potato virus Y; the turin strain was freed from these by taking inoculum from single lesions in Nicotiana glutinosa and Datura stramonium. In tobacco, cv. ‘White Burley’ or ‘Samsun’, the turin strain produced either necrotic rings, some of which were incomplete, or solid necrotic local lesions; the virus did not invade the plant systemically.