Cryopreservation of embryogenic cultures of Dioscorea bulbifera l. by encapsulation- dehydration

Embryogenic cultures of Dioscorea bulbifera were cryopreserved using an encapsulation- dehydration procedure with subsequent plant regeneration. Embryogenesis was induced by culturing in vitro grown axillary bud meristems on MS medium supplemented with 2.0 mg per liter 2,4-D. After cryopreservation, recovery growth of embryogenic culture up to 53.3 percent was recorded when excised proliferating embryogenic cultures of 1.5-2.0 mm in diameter were: encapsulated in 3 percent calcium alginate containing 0.15 M sucrose followed by preculturing with 0.5 M sucrose for 3 d; dehydrated in the laminar air flow for 4 h, thereby reducing the bead moisture content to 19.4 percent ( fresh weight basis); plunged into liquid nitrogen; thawed at 40 degree C; and cultured on recovery growth medium, i.e. MS supplemented with 2.0 mg per liter 2,4-D and 0.3 mg per liter BAP. However, preculturing for an extended period of 7 d increased the recovery growth further to 67.8 percent. During recovery growth the embryogenic tissue protruded out of the beads without loss of structural integrity of the cryopreserved embryos. Subculturing of these cultures on to embryo conversion medium, i.e. MS medium with 0.5 mg per liter zeatin and 400 mg per liter glutamine, resulted in production of plantlets through embryo conversion. The regenerated plantlets exhibited the same morphology as that of originally maintained in vitro plantlets and were established in vivo, in a net house with 80 percent success.