FIG. 6.

Hypothetical model for genetic exchanges among torovirus field variants. Torovirus genomes are depicted schematically, with the various genes represented by boxes. (A) Presumptive recombination event during PToV divergence, involving an ancestral PToV strain (P-Anc; genes indicated by white boxes) and an unknown toroviral parent (?; genes indicated by hatched boxes). Exchange of HE sequences resulted in recombinant progeny (P-Rec). (B) Presumptive recombination events during BToV divergence. During an initial single recombination event, the 3′ end of the HE gene and the N gene and the 3′-NTR of a BRV-like BToV variant (indicated in white) were replaced by the corresponding PToV sequences (dotted), giving rise to the B6/B145/B156/B1314 lineage. A subsequent double recombination event, during which BToV HE sequences were replaced by those of an as yet unidentified torovirus (?, indicated in black), resulted in the B150/B155 lineage.