Cryopreservation of shoot tips from in vitro plants of sweet potato [Ipomoea batatas (L.) Lam.] by vitrification

Routine cryopreservation of shoot tips from sweet potato [Ipomoea batatas ( L.) Lam] has been hampered by their survival variability after cryogenic ex posure. We examined the effects of light conditions on stock plants, sucros e preculture and cryoprotectant loading on survival after vitrification usi ng PVS2 solution. The survival of vitrified sweet potato shoot tips cooled to approximately -208 degrees C was increased by preculturing with 0.3 M su crose for 24 h at 22 degrees C. Survival was also enhanced by excising shoo t tips immediately after the 8-h dark photoperiod. The best survival after cryogenic exposure was obtained using 2 M glycerol + 0.4 M sucrose for 1 h at 22 degrees C followed by dehydration with PVS2 for 16 min at 22 degrees C. Rapid cooling was used and achieved by the immersion of foil strips into partially solidified nitrogen. Successfully vitrified and warmed shoot tip s directly developed shoots on a medium containing 1 mu M NAA, 0.5 mu M BA and 0.1 mu M kinetin with only minimum callus formation. Shoot formation oc curred in all surviving shoot tips. This procedure shows promise for cryopr eserving sweet potato shoot tips.