Identification of the rescued rJSTZ1712-12 and rJS-ORF2-6-CON in vitro. PRRSV-specific antigen was detected by the immunofluorescence assay (IFA) (A). The multiple-step growth curves in Marc-145 cells within 96 hpi were determined by real-time RT-PCR assay . No significant difference was observed in the in vitro replication of the parental and cloned viruses (B). The JSTZ1712-12, rJSTZ1712-12 and rJS-ORF2-6-CON viruses have similar plaque morphology (C).