Fig. 2.
Phylogenetic trees showing the relatedness among the 5′-terminal sequences (a), PLpro (b), Mpro (c), RdRp (d) domains and S1 glycoprotein genes (e) of 22 heterologous IBV strains. A cluster of contemporary field isolates and vaccine strains is indicated with a dashed box (⋯ ⋯) in a and in b. The neighbor-joining tree was constructed from the pairwise nucleotide differences for 5′-termini and deduced amino acid differences in all other respective genes. The length of each pair of branches represents the distance between sequence pairs. The scale at the bottom indicates the number of substitution events.