Cryopreservation of strawberry cv. 'senga sengana' by droplet vitrification
Droplet-vitrification method was applied to shoot tips of micropropagated Fragaria ×ananassa Duch. cv. ‘Senga Sengana’. Shoot tips of 2-3 mm in length were precultured in sucrose enriched media for 24 and 48h. Subsequently, shoot tips were transferred into 6 µl droplets of PVS2 vitrification solution for 20 min and plunged afterwards into liquid nitrogen. The effect of sucrose concentration (0.1, 0.25, 0.5, 0.75, 1.0 M) used in preculture of the shoot tips regarding their regrowth, histological changes and the morpholocical stability of the regenerants in the field was analysed. The highest recovering rate (67.7%) was achieved after a preculture with 0.25 M sucrose for 24h. Recovered shoots started to multiply considerably enhancing thereby the number of plantlets ready to transfer for acclimatisation. For field evaluation 22 to 165 plants per sucrose concentration were evaluated. The number of off-types was affected by the sucrose concentration used in preculture. Light and electron microscopy revealed starch accumulation in meristematic cells after preculture in sucrose. Ultra-structure of the meristematic cells was severely affected by PVS2 and liquid nitrogen treatment.