INTERACTIONS OF TOBACCO RINGSPOT AND BEAN POD MOTTLE VIRUSES WITH SOYBEAN MOSAIC VIRUS IN INFECTED SOYBEAN PLANTS, WITH OBSERVATIONS ON THE PARTICLE COMPLEXITY OF TOBACCO RINGSPOT VIRUS

Symptomatic synergism in mixed infections of soybean with soybean mosaic virus (SMV) and tobacco ringspot virus (TRSV), or with SMV and bean pod mottle virus (BPMV), was associated with effects on virus production. TRSV production was enhanced in mixed infections of SMV with TRSV, as compared to virus production in plants infected with TRSV alone. BPMV production was enhanced in mixed infections of SMV with BPMV, as compared to virus production in plants infected with BPMV alone. SMV production in inoculated primary leaves was inhibited by inoculation with either TRSV and BPMV. Top necrosis and classical bud blight symptoms were characteristic of mixed infections with SMV and TRSV and not of infections with TRSV alone. Development of these symptoms depended on the simultaneous replication of SMV and TRSV. Similarly, a top necrosis characteristic of mixed infections with SMV and BPMV also depended on the simultaneous replication of these two viruses. None of the synergistic effects observed was associated with enhanced transmission of the viruses through seed. The hitherto unreported existence of two sizes of particle in TRSV preparations was established from the centrifugal properties (sedimentation and density) and electron microscopy of the several particle categories previously recognized.