Purification and coat protein gene sequence of a Montana RMV-like isolate of barley yellow dwarf virus

A Montana barley yellow dwarf virus (BYDV) isolate, BYDV-RMV-MT, is serologically identical to the New York RMV type isolate (RMV-NY) but differs in aphid transmission phenotype. A purification procedure for BYDV-RMV-MT was developed and cDNAs encompassing the entire coat protein gene and a portion of the putative polymerase gene of both RMV-MT and RMV-NY were cloned and sequenced. Diameters of RMV-MT virions averaged 24.7 nm. Average virus yield was 4.2 mg/kg plant tissue. There was 81% sequence identity between the clones of MT and NY RMV isolates at the nucleotide level. At the amino acid level the polymerase genes were 91% identical to each other and 74% homologous with that of beet western yellow virus. The coat protein amino acid sequences of the two RMV isolates were only 81% identical and, compared to other sequenced luteoviruses, both were most similar to cucurbit aphid-borne yellows virus.