Evidence for three groups of sequence variants of beet necrotic yellow vein virus RNA 5

About half of Japanese isolates of beet necrotic yellow vein virus (BNYVV) were found to contain RNA 5 molecules, which were also detected in virus is olates from China and France. Sequence comparisons of RNA 5 (nucleotides 32 7 to 1171) in 25 isolates showed that there are up to 8% sequence differenc es, and that RNA 5 variants fall into three groups: group I contains most o f the Japanese and Chinese isolates, group II two Japanese isolates, and gr oup III four French isolates. The group I isolates fall into three small cl usters. In the 26 kDa coding region of RNA 5, there was a maximum of 1.5% n ucleotide sequence differences (6 amino acid changes) within the group and 8.4% nucleotide sequence differences (17 amino acid changes) between the gr oups. Comparisons of the coat protein gene of RNA 2 revealed that most of t he Japanese and Chinese isolates belonged to the A type strain, but some is olates were of the B type. The French isolates (P type) were closely relate d to those of the A type. Mixed infections of the two types of virus and th e two groups of RNA 5 were detected in a small area of Hokkaido. BNYVV migh t have been introduced into Japan and China by a similar route from at leas t two origins. These results, together with other evidence, suggest that th e three groups of RNA 5 variants separated from an original population a lo ng time ago and, thereafter, the group I population diverged further into t hree clusters, which may have been associated with the A type strain rather than the B type.