Abstract: The M genes of 63 infectious bronchitis viruses strains isolated in China from 1993 to 2010 were cloned and sequenced by RT-PCR to investigate the molecular epidemiology and genetic variation. Their sequences were also compared with those published in GenBank. The results showed that the nucleotide sequences of M gene had 6 different lengths. The nucleotide different in length resulted from insertion or deletion at the 5' terminus of M gene. There were 1 or 2 N-glycosylation site at the N terminus of M gene. The N-glycosylation site Asn-Cys-Thr was most conservative. The amino acid sequence similarities of M genes of 63 isolates were 87.2% to 100%. The amino acid sequence similarities of M genes of 63 isolates and referenced strains were 88.9% to 100%. 9 gentypes could be found among 63 IBV isolates in this study by the phylogenetic analysis. Most of IBV strains isolated in China from 2005 to 2010 were in different genotypes from vaccine strains of mass-genotype. The amino acid sequence similarities of M genes of the isolates from 2005 to 2010 and vaccine strains of mass-genotype were less than 94%.

Key words: IBV; M gene; genetic variation; phylogenetic analysis