Abstract
By means of polymerase chain reactions, nucleotide sequence analyses of the 3'-terminal regions, and amino acid sequence analyses, two capillovirus isolates, apple stem grooving (ASGV) and citrus tatter leaf virus (CTLV) were found from virus culture V3 obtained from a single shoot of Japanese pear (Pyrus serotina). V3 was originally presumed to be a pure culture of ASGV. The two isolates that were eventually determined to be different capilloviruses were designated V3-1 and V3-2, respectively. V3-1 differed from ASGV reference isolate P-209 from apple by only 3 base substitutions in the 3'-terminal 2611 nucleotides. V3-2 was closer to CTLV reference isolates Li-23 (95.9% homology) and L (95.6% homology) from lilies in the sequence of its 3'-terminal 1669 nucleotides than it was to that of ASGV isolate P-209 (89.1% homology). In the comparison of ORF2 proteins (313 amino acids, aa) the similarity between as sequences of V3-2 and P-209 was 94.8%, while that between V3-2 and CTLV isolates (Li-23 and L) was 97.4%. In the case of the as sequence homology of the putative coat protein regions (237 aa), equivalent to the C-terminal region of ORF1 protein, the similarity between V3-2 and P-209 was 97.5% and was 99.2% between V3-2 and CTLV isolates (Li-23 and L). The most striking difference in aa sequence homologies was found in the ORF1 protein (277 aa) encoding ORF2 in the other frame. The similarity between V3-1 and P-209 was 99.3%, while that between V3-2 and P-209 was 61.0%. Isolate V3-2 shared 85.6% and 93.8% aa sequence homologies with Li-23 and L, respectively. Solely on the basis of comparison of nucleotide and amino acid sequences of Japanese pear isolates V3-1 and V3-2 with reference isolates, we conclude that V3-1 is almost identical to an ASGV reference isolate from apple, while V3-2 is similar to CTLV reference isolates from lilies. We recommend that CTLV be considered as a strain of ASGV.
