Fig. 9. Phylogenetic tree of 198 amino acid residues in the L1 loop of the hexon gene of the fowl adenovirus (FAdV) isolates of this study and of 30 reference FAdV strains retrieved from GenBank. All isolates in SPF CEE from passage 5 (E5) (UPM1137E5) to E20 (UPM1137E20) (shaded in dark gray) were classified as Group E species (shaded in light gray) and were closely related to serotype 8b strains. The early passage isolates E5, E10, and E15 (shaded in dark gray) shared a common ancestor with other Malaysian FAdV strains. The high passage E20 (UPM1137E20) isolate (shaded in dark gray) was closer to the 430-06 and Australian FAdV strains and diverged from the earlier passages isolates. Groups A to E comprised of FAdV strains under serotype 1; serotype 5; serotype 4 and 10; serotype 2, 3, 9, and 11; serotype 6, 7, 8a, and 8b, respectively.