Efficiency of eradication of Raspberry bushy dwarf virus from infected raspberry (Rubus idaeus) by in vitro chemotherapy, thermotherapy and cryotherapy and their combinations

Raspberry bushy dwarf virus (RBDV) is one of the few horizontally transmitted plant viruses and is difficult to eradicate from infected raspberry (Rubus idaeus) by conventional methods because of its ability to infect meristematic cells in the apical dome. This virus is present where ever raspberry is grown and its adverse effects on quality and yield of the crop has necessitated development of methods to eradicate RBDV from infected stock plants. We applied ribavirin treatment (30 mg/L for 2 weeks—chemotherapy), thermotherapy (24 °C for 8 h in dark and 39 °C for 16 h with light for 2 weeks), cryotherapy (droplet vitrification of shoot tips) and their different combinations to assess the efficiency of virus eradication from an infected raspberry genotype. Virus testing was done on plantlets in tissue culture after 3–4 months following plant regeneration and repeated in half the population of virus-free plants in the greenhouse, 1 year after the initial test. Results showed that ribavirin treatment severely affected plant regeneration, resulting in low efficiency of virus eradication (10.6% regenerated plantlets free of RBDV out of all explants treated). When it was combined with thermotherapy, plant regeneration was significantly improved, resulting in higher efficiency of virus eradication (44.4%). When the shoot tips subjected to these two treatments were cryopreserved and regenerated, virus eradication efficiency further improved to 58.5%. The control of this treatment where plant material was not treated in liquid nitrogen produced the highest efficiency of virus eradication (78.8%), partly because of better plant regeneration. Thermotherapy and cryotherapy when applied alone failed to remove the virus from infected material; however, when combined, 48.6% efficiency of virus eradication was recorded. Inclusion of in vitro thermotherapy in combination with chemotherapy or cryotherapy or both is important to improve efficiency of RBDV eradication from infected raspberry. Nevertheless this virus can be eradicated by different approaches, and our results are useful for planning virus eradication programmes based on the efficiency of eradication. It is important to test the virus status after greenhouse acclimation, as virus may be suppressed and not completely eliminated in some treatments at tissue culture stage, as shown in ribavirin treatment in our research.