Parental virus / reassortant PB2 PB1 PA HA NP NA M NS L17-MDV L171 L17 L17 L17 L17 L17 L17 L17 NIBRG-23 PR82 PR8 PR8 Tur-r3 PR8 Tur4 PR8 PR8 First step. Crossing NIBRG-23, UV-inactivated, and L17-MDV Clone  B3 PR8 PR8 L17 Tur-r PR8 Tur PR8 PR8 Clone  C2 PR8 L17 L17 Tur-r PR8 Tur PR8 PR8 Clone  C4 L17 L17 L17 Tur-r PR8 L17 PR8 L17 Clone  D1 PR8 L17 L17 Tur-r PR8 Tur L17 PR8 Second step. Back crossing of clones from the “First step” with L17-MDV Clone  C2/35 L17 L17 L17 Tur-r L17 L17 L17 L17 Clone  C4/88 L17 L17 L17 Tur-r L17 L17 L17 L17 Clone  D1/32 L17 L17 L17 Tur-r L17 L17 L17 L17 Clone  D1/33 L17 L17 L17 Tur-r L17 L17 L17 L17 The origin of the genes encoding the corresponding proteins of the virus: 1L17 or L17-MDV corresponds to A/Leningrad/134/17/57 MDV (H2N2); 2A/Puerto Rico/8/34 (H1N1); 3RG-modified HA of non-pathogenic NIBRG-23 (H5N1); 4NA of non-pathogenic NIBRG-23 (H5N1) identical to A/turkey/Turkey/1/2005 (H5N1).

Table 1: Generation of reassortants between NIBRG-23(H5N1) and L17-MDV(H2N2).