Relationship between Beet Ringspot, Potato Bouquet and Tomato Black Ring Viruses

SUMMARY: Serological and plant-protection experiments provided evidence that potato bouquet and beet ringspot viruses are strains of tomato black ring virus. Tomato black ring and potato bouquet viruses are more closely related to each other than either is to beet ringspot virus. The three produce similar symptoms and have a similar host range. There was no evidence that they are related to tobacco ring spot or peach yellow bud mosaic viruses. In the plant-protection tests, protection between serologically related virus strains often was not reciprocal; when protection was incomplete, the symptoms produced by the second virus were milder than those in plants infected by it alone. Strains of tomato black ring virus could be arranged in order of their ability to cause symptoms in plants already infected with other strains. Although results of the plant-protection and serological tests agreed broadly, the correlation was not complete, suggesting that the tests measure different properties of the virus particles. The degree of difference between strains of tomato black ring virus seems to reflect their geographical separation, something that is perhaps to be more expected with soil-borne than with other viruses.