CALANTHE MILD MOSAIC-VIRUS, A NEW POTYVIRUS CAUSING A MILD MOSAIC DISEASE OF CALANTHE ORCHID IN JAPAN

Calanthe mild mosaic potyvirus (CalMMV), a previously undescribed viru s found in several locations in Japan, causes mild leaf mosaic and flo wer colour breaking of Calanthe plants. CalMMV was mechanically transm itted only to Calanthe sp., Phalaenopsis sp. and Tetragonia expansa of 50 plant species tested and was transmitted by the aphid Myzus persic ae in a nonpersistent manner. The virus has flexuous particles about 7 64 nm long and induced the formation of intracellular cytoplasmic cyli ndrical inclusions. The virus particles contain a single polypeptide o f 32.0 kDa and a single RNA of mel. weight 3.1 x 10(6). As determined by immune-electron microscopy, CalMMV is distantly related to the Japa nese isolate of dendrobium mosaic potyvirus (DeMV-J), but it showed no serological relationship to any of seven other potyviruses. The seque nce of the 3'-terminal 1306 nucleotides of the viral genome was determ ined. The coat protein (CP) coding sequence is predicted to be 804 nuc leotides in length, encoding a protein of 268 amino acids with a calcu lated mel. weight of 30389. The 3' noncoding region is 169 nucleotides long and is followed by a polyadenylate tract. The amino acid sequenc e of the CP of CalMMV was 73% homologous to that of DeMV-J, but less t han 66% to other potyviruses.