The Effect of Sterilization and Storage Conditions on the Viability of the Spores of Cyathea delgadii

Abstract

Tests were conducted to evaluate the effects of various sterilization procedures on spores of Cyathea delgadii stored under different conditions with the intent of developing a strat- egy of ex-situ spore conservation of this declining species. Although the percentage of germination after two years of storage was relatively low for all storage and sterilization parameters, dry storage at -12?C resulted in the best survival rate. Elimination of bacterial and fungal contaminants was best when the spores were washed, treated with calcium hypochlorite, incubated, filtered, and washed again before sowing on medium containing Nystatin. The spores of some tree ferns in the Cyatheaceae lose their viability after a few weeks of storage (Page, 1979). The viabilility of Cyathea delgadii Sternb. spores is already decreased after only two months storage at 12?C and low humidity (Randi and Felippe, 1988a) and percent spore germination is signif- icantly decreased after six months of storage under the same conditions (Mar- condes-Ferreira and Felippe, 1984). In general, it is advisable to store fern spores at low temperature and low humidity, sometimes with the use of des- iccators (Dyer, 1979a). More recently, storage in darkness at room temperature and high humidity (imbibed) has been advised for some species (Lindsay et al., 1991). Before storing imbibed spores in the laboratory or before germination of spores stored dry, there is the need to sterilize them. Several chemicals have been used for this purpose (Dyer, 1979b), and either sodium hypochlorite (NaOCl) or calcium hypochlorite (Ca(OCl2)J4H2O) are the most commonly used. Unfortunately, most treatments that kill contaminant fungi and bacteria also reduce fern spore germination. Different concentrations of chemicals and duration of application have been used. Before germination, it is advisable to incubate the spores in darkness for a period of time: the fungi and bacteria start to grow and become more sensitive to the chemicals used for sterilization (Voeller, 1964; Schedlbauer, 1976). The objective of this investigation was to study different sterilization meth- ods and storage conditions in order to develop a procedure for maintaining a source of viable spores of Cyathea delgadii for ex situ conservation, because this species is rapidly disappearing from the Brazilian forests as consequence of commercial exploitation.