e ligation strategy, the genomic cDNA of rH120-S1/YZ was assembled by in vitro ligation using appropriate restriction sites as indicated.

2.4  Chicken embryo dwarf assay
To determine the recombinants’ pathogenicity in chicken embryos, 0.2 mL of rH120, rIBYZ, or rH120-S1/YZ virus (diluted to 1:100 in normal saline) was inoculated into the