3.4 Phylogenetic analysis
Phylogenetic tree of Meq gene sequences with other reference sequences revealed that all the current strains (except one -002 MDV strain) clustered together with earlier reported Indian strains from northern part of the country and with very virulent plus (vv+) ATE 2539 strain from Hungary (Fig. 1). One MDV strain (MK388077) of present study clustered closely with two Italian strains (MK139661 and MK139672). Two Indian MDV strains TNN1 (HM749324) and TNN2 (HM749325) reported earlier from southern part clustered away from present strains.
The phylogenetic tree of pp38 gene showed clustering of the current 11 MDV field strains with other Indian strains from north and southern part of the country. It also clustered with two Chinese strains DY04 (HQ638161) and XJ03 (HQ638175). The other cluster included vaccine strains, mild (m), virulent (v) and very virulent (vv) strains (Fig. 2).
The phylogenetic tree of the vIL-8 gene showed that all 13 sequences of present study clustered with very virulent (vv) and very virulent plus (vv+) strains from USA and one strain from China. The sequences of other Indian strains from Southern part also fell on the same cluster. Mild and vaccine MDV strain formed a separate cluster (Fig. 3).