CRYOPRESERVATION OF NONENCAPSULATED EMBRYOGENIC TISSUE OF SWEET-POTATO (IPOMOEA-BATATAS)

Embryogenic tissue of the sweet potato (Ipomoea batatas (L) LAM) genot ype TIB 10 was established from in vitro axillary shoot tips on Murash ige and Skoog (1962) medium supplemented with 5 mu M 2,4-dichloropheno xyacetic acid. Embryogenic aggregates of fresh mass 9.0 - 12 mg were s ubjected to a rapid freezing protocol in liquid nitrogen following suc rose preculture and varying degrees of dehydration. Up to 50% of embry ogenic explants survived rapid freezing after preculture on 0.4 or 0.7 M sucrose only. Dehydration with silica gel to moisture contents in th e range 18-41% improved the survival after cryopreservation of embryog enic tissue. Tissue dehydrated for intermediate periods exhibited poor survival. Following freezing, embryogenic tissue appeared to develop normally, retaining its competence to produce mature embryos and plant lets.