A variant turkey herpesvirus (HVT/VT) which releases 10(5.0) plaque-forming units per 0.1 ml of cell-free virus into the culture medium was established from the prototype HVT FC 126 strain (HVT/WT). Many enveloped and naked virions of HVT/VT but only naked virions of HVT/WT were found in the culture medium. By the HindIII restriction cleavage patterns, the HVT/VT DNAs were almost identical to those of HVT/WT. The HVT/VT was replication-defective in chickens.

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Three substrains were cloned from chick kidney cell monolayers infected with the Ishii strain of lentogenic Newcastle disease virus isolated in Japan. These substrains, which differed in plaque morphology, were distinguished as having no +24R+ and -24R- patterns in the hemagglutination (HA)-elution test.