Fig. (1) Recombination between two PRRSV infectious clones P129-EGFP-97C and P129-GFPm-d (2-6). P129-EGFP-97C is a fully functional non-fluorescent virus and P129-GFPm-d (2-6) is a fluorescent defective virus lacking ORF2-6. Successful recombination between the two parental viruses is evidenced by producing viable fluorescent progeny viruses.