Genotypic and phenotypic variation of biotypes coexisting in the Hickman strain of Newcastle disease virus.

Many Newcastle disease virus strains are composed of several biotypes which coexist in the wild and in laboratory cultures. We have studied some of the phenotypic and genotypic properties of 6 virus clones from the coexisting biotypes of the Hickman strain of Newcastle disease virus. These clones were readily distinguishable from the parent virus strain and from each other by their RNA fingerprints. Fingerprints of the most virulent clones (Hi/LC, Hi/MC, and Hi/LR) contained 61% to 77% of the oligoribonucleotides present in the fingerprint of the Hickman parent strain. None of the clones killed chickens as rapidly as did the parent strain, although some clones killed embryonating eggs as rapidly as did the parent strain.