CRYOPRESERVATION OF EMBRYOGENIC TISSUE OF A RANGE OF GENOTYPES OF SWEET-POTATO (IPOMOEA-BATATAS [L] LAM) USING AN ENCAPSULATION PROTOCOL

Embryogenic tissue of nine sweet potato [Ipomoea batatas (L.) Lam] gen otypes from Asia, Africa and the Americas was established from in vitr o axillary buds on Murashige and Skoog medium supplemented with 2,4-di chlorophenoxyacetic acid or 2,4,5-trichlorophenoxyacetic acid. Embryog enic aggregates, 1.0-2.0 mm in diameter, were encapsulated in alginate gel, precultured on medium containing elevated levels of sucrose and dehydrated prior to rapid freezing in liquid nitrogen. The maximum sur vival of embryogenic tissue ranged from 4% to 38%, depending on the ge notype. With the incorporation of a slow-cooling step, survival was ge nerally much higher than that obtained after rapid freezing alone. Fiv e of eight genotypes tested with this protocol gave survival percentag es in excess of 55%, and a further two in excess of 33%, all after eva porative dehydration. The most effective sucrose treatment(s), however , varied with the genotype.