Identification and Detection of Two Major Viruses Infecting Orchids by Molecular Technique

Based on reported Cymbidium mosaic virus（CyMV）and Odontoglossum ringspot virus（ORSV）genomic cDNA sequences, two pairs of PCR primers for viral coat protein gene with expected ampliffied sizes of 784bp and 604bp were designed respectively, and RT-PCR was performed with the total RNA as templates extracted from diseased orchid plants (Cymbidium sinense var. margicoloratum and Oncidium sp.) collected from Shunde, Guangdong province, China. Five amplified DNA fragments with expected sizes were cloned and sequenced. Although the nucleiotide sequences of DNA fragments amplified from different orchid species or different farms with CyMV primer showed slightly diversity, they had highly homology to cp gene of CyMV isolates around the world. Otherwise, the nucleiotide sequences of the two DNA fragments amplified from different orchid species with ORSV primer were completely identity and highly homologous to cp gene of ORSV isolates around the world. Therefore the two viruses infecting orchids in Guangdong were identified as CyMV and ORSV. Simultaneous detection of the two orchid viruses by dual RT-PCR was conducted with primers mixture. Out of the 153 samples collected from 23 farms, 76 tested positive for CyMV, 52 positive for ORSV and 2 positive for both CyMV and ORSV.