Cryopreservation of cassava in vitro-grown shoot tips cooled to -196 degrees C by vitrification.

We first succeeded in the cryopreservation of cassava by a simple vitrifica tion procedure. Shoot tips of cassava (Manihot esculenta Crantz, cv.CM3281- 4) were excised from two-week-old in vitro-grown plantlets and precultured on solidified MS basal medium supplemented with 0.3 M sucrose for 16 h. The precultured shoot tips were treated with a mixture of 2 M glycerol plus 0. 4 M sucrose for 20 min at 25 degrees C and then dehydrated with a vitrifica tion solution (PVS2) for 45 min at 25 degrees C prior to a plunge into LN. Successfully vitrified shoot tips resumed growth within a week and develope d shoots without intermediary callus formation. The average rate of normal shoot formation amounted to 75%. Thus, this simple protocol by vitrificatio n appears promising as a practical method for cryopreservation of cassava g ermplasm.