Efficacy of meristem tip culture, thermotherapy, chemotherapy, cryotherapy and their combination for the remediation of Raspberry leaf mottle virus, Rubus yellow net virus and Raspberry latent virus on Rubus idaeus in vitro

In agriculture, viral pathogens are a major concern for farmers in terms of reduction of crop quality and yield. Raspberries, part of the genus Rubus genus (Rosaceae), have an important economic role in Canada. However, raspberry bushes are susceptible to numerous viral infections. Insects are the primary vectors for plant virus transmission with aphids being responsible for the transmission of over 50 % of viruses. The large raspberry aphid, Amphorophora agathonica, is responsible for the transmission of the raspberry leaf mottle virus (RLMV), the Rubus yellow net virus (RYNV) and the raspberry latent virus (RpLV). When present in combination, these viruses form a viral complex called raspberry mosaic disease (RMD) which induces severe symptoms in infected plants that has been linked to synergistic interaction. Several methods have been successful in eliminating viruses from plants including meristem tip culture, thermotherapy, chemotherapy and cryotherapy. However, there is still no clear evidence if synergistic activity affects the efficacy of these treatment. In this study, I aimed to shed light on synergistic interactions between viruses involved in the RMD viral complex on infected raspberry plants treated with thermotherapy, chemotherapy, cryotherapy and their combinations. To test for the presence of raspberry viruses, I optimized a one-step RT-qPCR on crude plant extract for rapid screening and a two-step RT-qPCR using RNA for individual testing. In vitro raspberry cultures were subjected to shoot tip dissection followed by thermotherapy, chemotherapy, cryotherapy or their combination, then a second meristem dissection post-treatment. Virus screening was done on leaf-petiole crude extracts using a one-step RT-qPCR. Results show that RLMV and RpLV can be eliminated using meristem-tip culture when they are present in single infection. RYNV was not eliminated from any of the plants infected with multiple viruses. RYNV is part of the Badnaviruses genus, which are known to integrate into their host's genome. qPCR is not able to distinguish the presence of viruses in their episomal or endogenous forms.