CRYOPRESERVATION OF ALGINATE-COATED INVITRO-GROWN SHOOT TIPS OF APPLE, PEAR AND MULBERRY

Alginate-coated shoot tips from in vitro-grown apple (Malus domestica Borkh cv Fuji) were successfully cryopreserved following dehydration. Shoot tips cold-hardened at 5-degrees-C for 3 weeks, were progressively precultured on MS agar media with increasing sucrose (0. 1, 0.4 and 0.7 M) daily at 5-degrees-C. The precultured shoot tips trapped into alginate-coated beads containing 0.5 M sucrose were treated in a medium supplemented with 1.0 M sucrose for 16 h at 5-degrees-C. Beads containing 1 shoot tip were then dehydrated up to about 33% water content (fresh weight basis) on sterile dry silica gel at 25-degrees-C before being immersed in liquid nitrogen (LN). The average rate of shoot formation after warming was about 80%. This method was successfully applied to three apple, one mulberry and three pear species or cultivars. This encapsulation-dehydration method also permitted the shoot tips to be stored at - 135-degrees-C for 5 months with little or no decrease in the rate of shoot formation. This modified method appears to be a promising technique for cryopreserving shoot tips from in vitro-grown plantlets of deciduous trees.