INTERACTIONS BETWEEN SATELLITE TOBACCO MOSAIC-VIRUS, HELPER TOBAMOVIRUSES, AND THEIR HOSTS

Satellite tobacco mosaic virus (STMV) was detected frequently in California in association with TMV-U5 in naturally infected plants of Nicotiana glauca. Replication of STMV was not helper virus specific because eight tobamoviruses were able to support its replication in experimental infections in hosts that included crop plants such as tobacco and tomato. Two other tobamoviruses as well as several taxonomically distinct viruses could not serve as a helper. Infection with STMV did not alter symptoms induced by the helper viruses in any of the hosts tested. The level of accumulation of STMV-specific double-stranded RNA in infected plants was affected by the helper virus and the host used and was low in tomato, with TMV-U1 as helper virus and high in tobacco or N. glauca with TMV-U5 as helper virus. Yield of STMV from tobacco or N. glauca ranged from 1.8 to 3.0 mg per 10 g of leaf tissue. Yields of TMV-U1 and TMV-U5 were reduced 32-48% by coinfection with STMV. After serial passages through N. tabacum, STMV reappeared in some but not all subcultures of TMV-U5 that were initially free of detectable amounts of STMV but that had been derived from isolates that once had STMV. STMV did not appear after field isolates of TMV-U5 that were free of STMV when isolated were transferred.