SANITATION OF CITRUS VARIETIES AND/OR CLONES BY IN VITRO MICROGRAFTING IN CYPRUS AND GREECE

The in vitro micrografting technique has been used in Cyprus and Greece since 2000 and 2007, respectively, to free from virus and other pathogens valuable citrus varieties and/or clones. Twenty-six among lemon, orange, mandarin, pummelo and bergamot accessions were selected from Cyprus citrus plantations and from the Poros Arboricultural Station and the Stamatakos nurseries in Greece. Scions derived from these trees were grafted onto healthy sour orange rootstocks in the greenhouse of the Agricultural Research Institute, Cyprus, for new apical meristems to be obtained for micrografting or micrografting was performed directly with meristem obtained from elite mother trees onto Carrizo, citrumelo or Troyer rootstocks. All mother plants were tested for viruses and viroids by biological indexing, by ELISA for Citrus tristeza closterovirus (CTV) and by RT-PCR for viroids. All mother trees were found free of CTV, Citrus variegation virus (CVV), concave gum and impietratura, but were infected by Citrus exocortis viroid (CEVd) and/or other viroids, including Citrus cachexia viroid (CCaVd) and Citrus bent leaf viroid (CBLVd), otherwise noted as CVdI. Some mother trees were infected by Citrus psorosis virus (CPsV). The standard procedure of shoot-tip grafting technique was used for elimination of viroids and CPsV in the selected citrus isolates. Micrografted plants were re-grafted on sour orange seedlings in vivo, or potted directly in soil and those successfully established were transferred to the glasshouse and tested 6-9 months later for the viruses and viroids present in the meristem donor mother plants. Citrus accessions produced by micrografting and found free of all viroids and CPsV were Cypriot lemon ‘Polyphori’ and ‘Lapithou’, ‘Arakapas’ mandarin, ‘Jaffa’ and ‘Siekeriko’ orange, Bergamot, ‘Frappa’ and ‘Coumantantas’. Tests for viroids and CPsV are being continued for all plants which were produced by shoot-tip grafting in vitro.