Newcastle disease virus attenuated strain for expressing infectious bursal disease virus variant VP2 protein as well as preparation method and application of Newcastle disease virus attenuated strain

The invention discloses a Newcastle disease virus attenuated strain for expressing infectious bursal disease virus variant VP2 protein as well as a preparation method and application of the Newcastle disease virus attenuated strain. The attenuated strain is constructed by inserting an infectious bursal disease virus variant VP2 protein gene between P-M genes of an NDV gene VII type attenuated strain rSL strain. The preparation method comprises the following steps: firstly introducing a restriction enzyme cutting site between P-M protein genes of a genome main plasmid of an NDV gene VII type attenuated strain rSL strain, and then inserting a sequence containing an infectious bursal disease virus variant VP2 protein gene and the restriction enzyme cutting site between the P-M protein genes in a homologous recombination manner to construct a complete recombinant genome main plasmid; and co-transfecting BHK cells by using the main plasmid and three auxiliary plasmids for respectively expressing N, P and L protein