A comparison of six cypovirus isolates by cross-hybridisation of their dsRNA genome segments.

Genetic relationships between the genome segments of six cypovirus (CPV) isolates were analysed by RNA cross-hybridisation. These included three type 1 viruses and single isolates of types 2, 5 and 12, which collectively are identical to those previously compared by serology and electrophoresis [Mertens et al. (1989), J Gen Virol 70: 173-185]. Since only genome segment 10 of three cypovirus types and segments 8 and 9 of a single virus strain (of type 1) have currently been sequenced, this initial study provides some additional information on sequence variation/similarity in each of the ten genome segments. The RNA of the type 1 viruses showed high levels of cross-hybridisation. Significant but much lower levels of cross-hybridisation were detected between type 1 and the related type 12 CPV. However, only very low levels of cross-hybridisation were detected between the other pairs of viruses. Apart from evidence of a slightly higher level of sequence similarity between the largest segments, the RNA sequence appeared to vary uniformly across the whole genome. There was no evidence for any type specific RNA sequences restricted to individual genome segment(s). The sequence variation, reflected in the levels of RNA sequence similarity and cross hybridisation, correlates well with serological data, showing large differences between CPV types and supports the continued use of electropherotype as one of the 'species parameters' for the classification of cypoviruses.