172 • Technologies To Maintain Biological Diversity 



formation of ice, resulting in damaged cells and 

 death of seeds. Instead, plants with recalcitrant 

 seeds are commonly stored as field collections. 

 Research on the physiology of recalcitrant seeds 

 may lead to methods for long-term seed main- 

 tenance of these species. In vitro plantlet or em- 

 bryo culture, coupled with cryogenic storage, 

 may also eventually become useful for these 

 species. 



Two other biological limitations may restrict 

 the maintenance of some plants. First, the qual- 

 ities that distinguish a particular variety (e.g., 

 flower color and shape in roses; or the color, 

 flavor, and texture of a peach) may not be pre- 

 served in plants grown from seeds. For many 

 fruit and nut varieties, retention of these spe- 

 cific qualities is only possible through clonal 

 propagation, which entails producing plants 

 from cuttings or by grafting. Second, some 

 plants do not produce seeds readily because of 

 inappropriate environmental conditions, phys- 

 iological barriers, or genetic inabilities. In some 

 cases, such as many varieties of banana or the 

 tropical yams (Dioscorea), plants are sterile and 

 seeds cannot be obtained. Basic studies of phys- 

 iology are needed to improve understanding 

 of the processes controlling flowering and seed 

 production for both cultivated and wild plant 

 species. 



Reliability 



The reliability of technology refers to both 

 the potential for loss (by natural causes, acci- 

 dent, or equipment failure) and the likelihood 

 of genetic alteration during storage. 



The potential for loss by natural causes is 

 higher in field collections than in seed collec- 

 tions. Pests, diseases, and environmental con- 

 ditions can decimate field collections. Therefore, 

 collections should be duplicated in different 

 locations to ensure against loss. Greenhouses 

 or other controlled environments may reduce 

 the potential for loss by reducing environmental 

 exposure. Research oiin vitro culture may lead 

 to alternatives to field collections that are free 

 from disease and environmental uncertainties. 



Collections are also subject to equipment fail- 

 ure. As a backup measure, mechanical refrig- 



eration compressors should have alternative 

 power systems to prevent warming, which may 

 adversely affect the viability of stored seeds 

 (100). Cryogenic techniques do not rely on ex- 

 ternal power sources or mechanical cooling sys- 

 tems. And though containers may develop 

 leaks, the risks to security are considered much 

 less than for mechanical refrigeration (100,101). 



Some novel approaches to reducing depen- 

 dence on mechanical cooling systems are be- 

 ing tested. The Nordic Gene Bank in Sweden 

 recently established a long-term storage facil- 

 ity in old mines dug into the permafrost (125). 

 The Polish Government proposed establishing 

 a world seed collection in Antarctic ice caves, 

 but this approach raises questions about stor- 

 age temperatures and about ease of access and 

 political control (55). An approach being de- 

 veloped in Argentina is to use the cold nights 

 of mountain environments to cool a specially 

 constructed storage vault (55). These options, 

 while interesting, are suitable for only certain 

 countries and are still experimental. 



Genetic stability of plants can be affected in 

 several ways. Mutations in orthodox seeds may 

 increase as samples lose their ability to ger- 

 minate (84,108). Growing out samples subjects 

 them to conditions that will select against cer- 

 tain individuals and thus reduce genetic diver- 

 sity in the sample (88). Cryogenic storage can 

 improve genetic stability by slowing viability 

 loss and lengthening the time needed between 

 regenerations. For in vitro cultures, genetic mu- 

 tation becomes a concern when the tissues are 

 growing as unorganized calli. Cryogenic stor- 

 age of such cultures could suppress mutation 

 by arresting growth, but more research on plant 

 development and cryopreservation of in vitro 

 cultures is still needed (90,108). 



Costs 



A final consideration in the selection of tech- 

 nologies is cost. In seed storage facilities, ex- 

 penses are incurred with monitoring viability 

 and regenerating samples. Mechanical refrig- 

 eration systems can be expensive because of 

 continuous energy costs. Cryogenic storage can 

 lower long-term costs by reducing the fre- 



