Method of preventing virus increase in plants

A method of isolating a material which inhibits replication of TMV, CMV and PVX comprising the steps of:

• isolating protoplasts of a plant of the genus Nicotiana tabacum L. having an N gene;
• inoculating the protoplasts with Tobacco Mosaic Virus;
• incubating the inoculated protoplasts under continuous illumination for between 24 and 96 hours;
• removing the protoplasts from the incubation medium;
• homogenizing the removed protoplasts in phosphate buffer;
• centrifuging the homogenate;
• and
• ultracentrifuging the supernate to remove the Tobacco Mosaic Virus.

A method of isolating a material which inhibits replication of TMV, CMV and PVX comprising the steps of:

• inoculating with Cucumber Mosaic Virus a plant of the genus Nicotiana tabacum L. which responds systemically to Cucumber Mosaic Virus;
• after about four weeks, separating "green islands" tissue from the remainder of the leaf;
• homogenizing the "green islands" tissue;
• centrifuging the homogenate;
• dialyzing the supernate against phosphate buffer;
• adding ZnAc.sub.2 to the dialyzed supernate to a final concentration of 0.02M;
• after about three hours, centrifuging the solution;
• dissolving the precipitate by bringing the solution to between pH 2.5-2.6;
• centrifuging the solution;
• and
• dialyzing the supernate against phosphate buffer.

A method of isolating a material which inhibits replication of TMV, CMV and PVX comprising the steps of:

• inoculating with Cucumber Mosaic Virus a plant of the genus Nicotiana tabacum L. which responds systemically to Cucumber Mosaic Virus;
• after about four weeks, separating "green islands" tissue from the remainder of the leaf;
• isolating protoplasts from said "green islands" tissue;
• inoculating the protoplasts with a virus selected from the group consisting of Tobacco Mosaic Virus and Cucumber Mosaic Virus;
• incubating the inoculated protoplasts under continuous illumination for between 24 and 96 hours;
• removing the protoplasts from the incubation medium;
• and
• sterilizing the incubation medium.