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IBV phylogenetic tree of S1 genes. The tree is based on the sequence of the S1 genes from the 10 IBV isolates and the 35 reference strains, and ClustalW alignment method for S1 nucleotide positions 25–1611 corresponding to those of strain Mass41 (GenBank accession number X04722). The IBV isolates are denoted in bold and two reference strains (KM91 and QXIBV) are underlined. The provisional designations, including genogroups and sub-genogroups, are indicated on the right.
