CRYOPRESERVATION OF EMBRYOGENIC TISSUE OF SWEET-POTATO (IPOMOEA-BATATAS) - USE OF SUCROSE AND DEHYDRATION FOR CRYOPROTECTION

Embryogenic tissue of two sweet potato (Ipomoea batatas (L) LAM) genot ypes, TIB 10 and Nemanete (Nem), was established from in vitro axillar y meristems on Murashige and Skoog (1962) media supplemented with 2,4- dichlorophenoxyacetic acid and 2,4,5-trichlorophenoxyacetic acid respe ctively. Embryogenic aggregates of approximately 1.5 - 2.0 mm in diame ter were subjected to a rapid or a two-step freezing protocol in liqui d nitrogen following alginate encapsulation, sucrose preculture and va rying degrees of dehydration. UP to 28% of encapsulated embryogenic ag gregates of TIB 10 survived rapid freezing without dehydration. This w as not enhanced by dehydration prior to freezing. However, survival af ter dehydration was enhanced up to 74% by incorporating an initial slo w cooling step prior to plunging the tissue into liquid nitrogen. Foll owing freezing, embryogenic tissue appeared to develop normally and re tained its competence to produce mature embryos and plantlets. Similar results were obtained with Nem, although the survival percentages wer e much lower.