Abstract:The presented assay of Cucumber mosaic virus strain(Cah1-CMV) contained full-length cloning,sequence analysis and host reaction tests,which was isolated from Canna in Hangzhou,China.RNA1 of Cah1-CMV was consisted of 3 356 nucleotides(nts),encoding 1a protein of 993 amino acids;RNA2 consisted of 3 045 nts,encoding 2a protein of 843 amino acids and 2b protein of 111 amino acids;and its RNA3 consisted of 2 220 nts,encoding 3a protein of 279 amino acids and CP protein of 218 amino acids,respectively.The results of phylogenetic analysis recommended that Cah1-CMV belonged to CMV subgroup IB.When inoculated onto typical CMV host plants,Cah1 induced systemic necrosis in N.glutinosa,but typical mosaic in other testing plants in Solanaceous Family.A recombinant virus FCah12b-CMV was constructed by replacing 2b gene of wild type Fny-CMV to that of Cah1-CMV.When FCah12b was inoculated on N.glutinosa,the top leaves were appearing brown and necrosis,similar to those induced by parental Cah1-CMV at the early stage of infection,but Fny-CMV did not induce similar symptom.At later infection stage,unlike Cah1-CMV,FCah12b-CMV did not cause systemic death.The Northern blotting showed that there was no significant dif-ference of viral RNA accumulation in systemic leaves infected by Cah1-CMV,Fny-CMV and FCah12b-CMV.The above results indicated that the 2b gene of Cah1-CMV played an important role in inducing viral symptoms,but it is not the determinant of symptoms on the whole plant.The differences in pathogenicity were not directly associated with the virus accumulation levels.