Two isolates of cucumber mosaic cucumovirus expressing mild mosaic symptoms on tobacco plants

Two cucumber mosaic virus (CMV) isolates that induce mild mosaic symptoms i n tobacco (Nicotiana tabacum L.) were characterized by symptom observation, serological tests and the nucleotide sequences of viral RNA. CMV-m2 but no b CMV-m1 elicited necrotic etching symptom in the inoculated leaves of toba cco. CMV-ml and CMV-m2 exhibited different serological properties. Comparis on of the nucleotide sequences of RNA3s showed that CMV-m2 belongs to subgr oup II of CMV. CMV-ml was suggested to belong to subgroup I with serologica l test and symptomatology. The two isolates that induce very mild mosaic sy mptoms in tobacco but belong to different subgroups of CMV would greatly fa cilitate the study on the molecular basis of cross-protection of plant viru ses.