Biological, serological, and molecular variabilities of clover yellow vein virus.
A comparative study was made on the host reactions, serological properties, and nucleotide sequences of the coat protein (CP) gene of 10 clover yellow vein potyvirus (ClYVV) isolates and 1 bean yellow mosaic potyvirus (BYMV) isolate collected from different host plant species and locations in Japan. Two strains of ClYVV isolates, grouped on the basis of host reactions on Chenopodium amaranticolor, C. quinoa, Nicotiana clevelandii, N. benthamiana, faba beans and Trifolium repens, corresponded to 2 serotypes determined by double-antibody sandwich- and triple-antibody sandwich ELISA using 3 polyclonal and 9 monoclonal antibodies. This was confirmed by nucleotide sequence analysis of the CP gene. The CP gene of ClYVV isolates of strain 1, including the Australian isolate ClYVV-B, had 93-98% nucleotide identities and 97-99.6% amino acid identities. The CP of ClYVV isolates of strain 2, including the New Zealand isolate CIYVV-NZ, had 92-98% nucleotide identities and 95-98% amino acid identities. The nucleotide identities and the amino acid identities between the 2 ClYVV strains were 82-84%, and 90-94%, respectively. When compared with the CP sequences of 12 ClYVV isolates, the CP sequence of the BYMV isolate had 71-73% nucleotide identity and 73-77% amino acid identity. Amino acid sequence differences among ClYVV isolates from strains 1 and 2 were located mostly at the N-terminal regions of the CP. It is concluded that the ClYVV isolates studied could be separated into 2 strains on the basis of host reactions, serology and the nucleotide sequence of the CP gene.