EFFECTS OF TEMPERATURE AND DESICCATION ON EX SITU CONSERVATION OF NONGREEN FERN SPORES

Premise of the study: Fern spores are unicellular and haploid, making them a potential model system to study factors that regulate lifespan and mechanisms of aging. Aging rates of nongreen spores were measured to compare longevity characteristics among diverse fern species and test for orthodox response to storage temperature and moisture. Methods: Aging of spores from 10 fern species was quantified by changes in germination and growth parameters. Storage temperature ranged from ambient room to -196 degrees C (liquid nitrogen); spores were dried to ambient relative humidity (RH) or using silica gel. Key results: Survival of spores varied under ambient storage conditions, with one species dying within a year and two species having greater than 50% survival after 3 years. Few changes in germination or growth were observed in spores stored at either -80 degrees C or -196 degrees C over the same 3-yr study period. Spores stored at -25 degrees C aged anomalously quickly, especially those dried to ambient RH or subjected to repeated freeze-thaw cycles. Conclusions: Spore longevity is comparable to orthodox seed longevity under ambient storage conditions, with wide variation among species and shelflife extended by drying or cooling. However, faster aging during freezer storage may indicate a similar syndrome of damage experienced by seeds categorized as "intermediate". The damage is avoided by storage at -80 degrees C or liquid nitrogen temperatures, making cryoconservation an effective and broadly applicable tool to extend fern spore longevity. The study demonstrates that spore banks are a feasible approach for ex situ conservation of this important plant group.