Using Dithiouracil and Ribavirin to Eliminate Cymbidium Mosaic Virus during Micropropagation of `Uniwai Mist' Dendrobium Orchid

Our objective was to develop a virucide-based method to eliminate cymbidium mosaic virus from infected dendrobium protocorm-like bodies during micropropagation. We tested two virucides—dithiouracil and ribavirin. The best treatments for recovery of virus-negative tissue and subsequent plant development were 0.1 m m ribavirin or 0.2 m m dithiouracil in liquid medium for 5 or 6 weeks followed by culture on solid medium with 0.1 m m ribavirin or 0.1 m m dithiouracil, respectively. Most propagules transferred to solid medium were virus-free at 17 weeks on ribavirin, with up to 100% free of virus after 32 to 38 weeks on ribavirin or dithiouracil. Virus loss among protocorm-like bodies cultured without virucides ranged from 0% to 37%. Most plants remained free of virus 2.5 years after chemotherapy and flowered normally.