The different pre- and post-treatments are critical in cryopreservation procedures and affect the shoot tip regrowth after freezing. In the present study, the long-term storage of four citrus cultivars [Bodrum Mandarin (Citrus deliciosa Ten.); Klin Mandarin (Citrus nobilis Lauriro); White grapefruit and Red grapefruit (Citrus paradisi L.)] were carried out by droplet vitrification methods, and the critical points for effective cryopreservation of these species were determined. In this study, we investigated the effect of explant size, cold hardening treatments, sucrose concentrations, and media combinations on shoot regrowth after cryopreservation. The highest shoot tip regrowth, ranging from 13.3 to 33.3%, was achieved when they were obtained from 0.3 to 0.7 mm explants excised from cold hardened seedlings at 4 °C for three days that were then precultured in a medium containing 0.25 M of sucrose and treated with PVS2 at 0 °C for 45 min. In addition, it has been determined that a regeneration medium containing boric acid (H₃BO₃) or ferric ethylenediaminetetraacetate (FeEDDHA) increased the regeneration up to 33.3% after cryopreservation.

Numerous plant species around the world suffer from the presence of viruses, which especially in economically important crops, cause irretrievable damage and/or extensive losses. Many biotechnological approaches have been developed, such as meristem culture, chemotherapy, thermotherapy or cryotherapy, to eliminate viruses from infected plants. These have been used alone or in combination. In this work, meristem culture, thermotherapy and cryotherapy were compared for Apple mosaic virus elimination from hazelnut local cultivar "Palaz". The virus-free plant was also confirmed by reverse transcriptase poly merase chain reaction (RT-PCR) after each treatment and, the best results were obtained by cryotherapy. A one step freezing technique, droplet vitrification, was used for cryotherapy, and the best regeneration percentage was 52%. After cryotherapy, virus-free seedlings of hazelnut local cultivar "Palaz" were confirmed as being virus-free after three subcultured periods.