Long term survival of cryptic viruses in aseptically grown in vitro propagated plants

Cryptic plant viruses are seed-borne dsRNA-viruses which co-exist with their host plants throughout their lives without inducing any symptoms. Since changing the growth conditions or altering the host-virus combination (cultivar, strain, isolate, etc.) may have a strong effect on virus multiplication we wanted to find out whether and if so what effect long term tissue culture has on the survival of carnation cryptic virus (CarCV). In vitro cultures of 18 different carnation species of a Hungarian germplasm collection were initiated from sterilised seeds 16 years ago and the plantlets have been grown aseptically since then. Genomic dsRNAs of CarCV were detected in Dianthus caryophyllus, D. superbus, D. carthusianorum and D. gratianopolitanus. In addition, in several cases 1-3 dsRNA-species ranging from 1100 to 3600 by were seen. The origin of the latter dsRNA is unknown. In addition to CarCV we have also been able to show that the beet cryptic viruses BCV1, -2 and -3 survive under in vitro conditions. After 5-7 years of cultivation in some but not all sugar beet plantlets quite high concentrations of BCV dsRNAs were detected. Our results indicate that cryptic viruses are so well adapted to their hosts that despite the dramatic change of environment they may survive for more than a decade of tissue culturing.