Spore germination and gametophyte development of tropical and subtropical pteridophytes and the suitability of their spores for long-term storage
Conservation of pteridophyte diversity presents a real challenge. Over 15% of the
c 9.000 known species are believed to be threatened with extinction and for most of the others the natural habitat is declining.
This project has therefore been carried out at the Botanical Garden Berlin-Dahlem (BGBM), to investigate the feasibility of long-term storage of spores of tropical and subtropical pteridophytes in a spore bank and assess the optimal conditions for doing so.
As a preliminary step in such a programme, it is necessary to test the viability of the fresh spores. The studies were carried out on cultivated material from the glas-houses of the BGBM and on spores of wild plants, most of them collected in Cuba in 1996. Freshly harvested spores were sown on different media and held at 22°±1°C and c 3000 Lux for 10 hours per day. In parallel more natural culture conditions (culture glas-house, window-sill), different light intensities and dark-imbibition of the spores were tested. Spore germination, gametophyte and sporophyte development of each species were investigated, and the successive stages documented to highlight species-specific peculiarities.
At the same time spores from each batch were dried and stored at deep-freeze temperature (-25°C), under herbarium conditions (room temperature) and refrigerated (at +4°C). Germination tests were then carried out at defined intervals up to three years to check viability decline.
The results gained range from species without signs of viability loss to those that lose viability dramatically within just two months of deep-freeze storage. The viability also depends on the storage type and differs for the species tested. Some species kept their viability nearly full up to about 1 or 2 years, showing a rapid decline afterwards.
These results underline the importance of tests on culture conditions and spore viability before a species is chosen for ex situ conservation of its spores by long-term storage.
The morphological part presents the results on spore and gametophyte morphology gained during the investigations. Pollution with extraneous spores may pose significant problems, especially in species with low germination rates. The knowledge of morphological significances facilitates an early identification of the prothallia. Since apogamous propagation in ferns is not unusual, it is important to know, whether the sporophytes are formed sexually or apogamously. Cytological investigations proved this for Adiantum hispidulum Sw. These results supply important hints for a successful species-specific cultivation.
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