Effects of Desiccation and Cryopreservation on theIn VitroViability of Embryos of the Recalcitrant Seed SpeciesAraucaria hunsteiniiK. Schum

Abstract

Pritchard, H. W. and Prendergast, F. G. 1986. Effects of desiccation and cryopreservation on the in vitro viability of embryos of the recalcitrant seed species (Araucaria hunsteinii K. Shum.—J. exp. Bot. 37: 1388-1397. Embryos excised from fresh seed had a moisture content of about 37% (fr. wt.), 7% above that of the whole seed: mainly as a result of the dryness of the seed coat. When cultured for 14 d at 26 °C embryo growth ranged from unorganized to fully organized. Embryos which had been directly surface sterilized exhibited lower fully organized growth than aseptically excised embryos. During desiccation of the whole seed at 15 °C and 15% r.h. moisture loss from the embryo was slow until the embryo reached a mean critical moisture content for fully organized growth in vitro of about 30%. After this point the rate of moisture loss increased, quickly diminishing the moisture content differential between the embryo and the whole seed. No such shoulder in the embryo desiccation curve was observed when using a low viability (7%) seed batch. When dried below 30% moisture content, such aseptically excised embryos increasingly exhibited unorganized growth in vitro, with only root meristem survival (46%) at 13% moisture content. In contrast, a much higher level of root meristem survival (84% of control) was observed when aseptically excised embryos were rapidly desiccated to 13% moisture content, using a flow of sterile air. However, the benefits of rapid drying were lost if the embryos were directly surface-sterilized prior to desiccation. Furthermore, 80% of aseptically excised embryos which survived rapid desiccation to 20% moisture content exhibited root meristem survival following subsequent cryopreservation. These findings have implications for the in vitro conservation of recalcitrant seed tissue. Key words— Araucaria hunsteinii K. Schum., recalcitrant seed embryo, desiccation, cryopreservation. Correspondence to: Jodrell Laboratory, Royal Botanic Gardens, Kew, Wakehurst Place, Ardingly, Sussex RH17 6TN, U.K.