对2000-2004年从中国9个省市分离到的13株IBV的核蛋白基因片段进行序列测定及分析的结果表明，13株IBV分离株核蛋白基因均含有一个长1230bp的ORF，但存在基因突变现象。与GenBank中的42株参考毒株核蛋白基因序列进行比较和分析，系统进化关系显示55株IBV毒株分属于9个群。第Ⅰ-Ⅲ群主要包括美国、日本、荷兰等国家以及中国的部分IBV分离株和疫苗株。其中本研究中的CK/CH/LHN/00I可能为一株分离的疫苗毒，CK/CH/LSD/03I、CK/CH/LDL/01I可能为重组毒。而中国近十年来分离的IBV毒株主要分布在第Ⅵ-Ⅷ群中，此3群内IBV毒株之间N蛋白推导氨基酸同源性为88.3%～100%，与其他各群之间同源性为62.3%～95.1%。因此，此基因型的IBV毒株可能在中国已有较长时期的存在且发生了较大程度的变异。其中第Ⅵ群中两株韩国分离株与中国IBV分离株具有较近的亲缘关系。以上结果表明，中国大多数IBV分离株在N基因进化关系上较为独立，与国外毒株相比，和韩国毒株进化关系密切。此外，中国IBV毒株基因重组现象更加普遍，尤其是疫苗毒和野毒之间的重组。

Nucleocapsid (N) protein genes of 13 Infectious bronchitis virus (IBV) strains isolated from 9 provinces in China between 2000 and 2004 were sequenced and compared to 42 IBV reference strains. The results showed that all of the N genes of the 13 isolates were composed of 1230 nucleotides, but point mutations were common. A phylogenetic tree based on amino acid sequences of N genes from the 55 IBV strains showed that these strains were classified into nine distinct clusters. 17 IBV isolates and 5 vaccines of America, Japan, Holland and China formed clusterⅠto cluster Ⅲ. CK/CH/LHN/00I might be a re-isolation of vaccine strains. Recombinations were observed in the isolates of CK/CH/LSD/03I and CK/CH/LDL/01I. However, IBVs isolated mainly in China between 1995 and 2004 were grouped into cluster Ⅵ to cluster Ⅷ.The deduced amino acid sequences identities of N genes among IBVs of the three clusters ranged from 88.3% to 100%, and 62.3% to 95.1% between these IBVs and those of other clusters. Hence, it was suggested that this genotype may have existed for a long time in China and have occurred with higher number of mutations. Two Korean isolates shared higher identity with Chinese IBV isolates of cluster Ⅵ. Taken together, these results showed that most of IBVs isolated in China formed distinct phylogenetic groups and had a close relationship with Korean isolates compared the foreign strains. On the other hand, recombination of IBV may have occurred at a rather high frequency in recent years in China especially between vaccine strains and field strains in the natural condition.