The Regeneration of Virus-Free Plants from Cucumber Mosaic Virus- and Potato Virus Y-Infected Tobacco Explants Cultured in the Presence of Virazole

The strategy for mass cloning of plants by micro­ propagation depends on disease-indexing the donor plant, and eliminating any diseases found, before setting up the explant or meristem cultures. Details of tissue culture media have been published for most commercially important species [1]. Fungal, bacterial and mycoplasmal pathogens can be successfully elim­ inated by the addition of the appropriate antibiotics to the culture medium, but the potential of micro­ propagation will be realized only when virus elim­ ination can be easily achieved. Presently, virus exclusion from the meristem and/ or differential thermal stability of virus and host tissue, are used to produce virus-free “elite” stock plants for subsequent cloning [2]. However, these procedures are not universally efficaceous, some viruses being particularly invasive or having relative­ ly high thermal stability [3, 4]. Furthermore, low virus titre or slow systemic movement may necessi­ tate repeated virus testing of the progeny plant be­ fore one can be reasonably confident of virus elimina­ tion and during this time there is risk of reinfection. Many of the potential antiviral chemicals devel­ oped by animal virologists have also been screened in plants but results so far have not been encourag­ ing [5]. Much of this work is speculative in plants, since many of the chemicals are uncharacterized in­ hibitors or were designed putatively, as inhibitors of