Cryopreservation of African violet (Saintpaulia ionantha Wendl.) shoot tips

Cryopreservation of African violet via encapsulation-dehydration, vitrification, and encapsulation-vitrification of shoot tips was evaluated. Encapsulation-dehydration, pretreatment of shoot tips with 0.3 M sucrose for 2 d followed by air dehydration for 2 and 4 h resulted in complete survival and 75% regrowth, respectively. Dehydration of encapsulated shoot tips with silica gel for 1 h resulted in 80% survival but only 30% regrowth. Higher viability of shoot tips was obtained when using a step-wise dehydration of the material rather than direct exposure to 100% plant vitrification solution (PVS2). Complete survival and 90% regrowth were achieved with a four-step dehydration with PVS2 at 25degreesC for 20 min prior to freezing. The use of 2 M glycerol plus 0.4 M sucrose or 10% dimethyl sulfoxide (DMSO) plus 0.5 M sucrose as a cryoprotectant resulted in 55% survival of shoots. The greatest survival (80-100%) and regrowth (80%) was obtained when shoot tips were cryoprotected with 10% DMSO plus 0.5 M sucrose or 5% DMSO plus 0.75 M sucrose followed by dehydration with 100% PVS2. Shoot tips cryoprotected with 2 M glycerol plus 0.4 M sucrose for 20 min exhibited complete survival (100%) and the highest regrowth (55%). In encapsulation-vitrification, dehydration of encapsulated and cryoprotected shoot tips with 100% PVS2 at 25degreesC for 5 min resulted in 85% survival and 80% regrowth.