FIG. 4.

Plaque morphology of mutant NDVs containing F-HN and HN-L IGSs with increased or decreased lengths. Recovered viruses were titrated in duplicate in six-well plates. Supernatants collected from virus-inoculated samples were serially diluted, and 0.2 ml of each diluent per well was added to confluent DF-1 cells. After 1 h of adsorption, cells were overlaid with DMEM containing 2% FBS and 1% methylcellulose and incubated at 37°C for 4 days. The cells were then fixed with methanol and stained with crystal violet.