Figure 5. Neighbour-joining tree showing relationships between Seg-6 of NET2008/05 with other BTV-6 isolates and the twenty-five reference strains of different BTV serotypes.

The seven evolutionary branching points are indicated by black dots on the tree (along with their bootstrap values), dividing the sequences into eight ‘Seg-6 nucleotypes’ designated ‘A–H’. In previous studies [72], six Seg-6 nucleotypes were identified, however the additional analyses described here indicate that the previous ‘nucleotype C’ should be subdivided (into nucleotypes ‘C’ and ‘G’). BTV-25 (Toggenburg orbivirus [TOV]) forms a new 8^th Seg-6 nucleotype (H). Members of the same nucleotype show >76% nt identity in Seg-6, while members of different nucleotypes show <76% nt identity (see Figure 3).