RESUMEN
Tobacco streak virus (TSV) is an important emerging virus belongs to the genus Ilarvirus and family Bromovidae. The Onion crop is infected by Tobacco streak ilar virus and it is major problem in different places of Andhra Pradesh in South India and also transmitted by thrips vector. TSV suspecting onion samples were identified by direct antigen coating enzyme linked immunosorbent assay using TSV polyclonal antiserum. The Replicase gene from each isolate was amplified using TSV replicase gene specific primers by using the RT-PCR. The ~530 bp product was amplified, cloned, sequenced and determined its length as 534 nucleotides and codes for 178 amino acids. The partial sequence of TSV-Rep shared identity of 87.6 -99.8% at nucleotide levels and 67.8- 99.4% at amino acid levels respectively with other reported TSV isolates. The phylogenetic tree relationship based on the nucleotide sequence of present study isolate (AP-Onion-Chittoor) from different geographical regions was also analyzed in this study.