180 • Technologies To Maintain Biological Diversity 



Figure 7-2.— Maintenance Process of a 

 Plant Seed Banl( 



SOURCE: Office of Technology Assessment, 1986. 



as seeds, in fields, or in greenhouse collections. 

 Pollen storage and in vitro plantlet cultures may 

 supplement storage of many of these species. 

 Finally, cryogenic storage (in liquid nitrogen) 

 and emerging DNA technologies may hold po- 

 tential for improving maintenance of plants. 



Conventional Seed Storage 



Most agricultural crops held by the National 

 Plant Germplasm System (NPGS), international 

 centers, national programs, and private collec- 

 tions are maintained as seeds. The process of 

 conventional seed storage can be divided into 

 several steps: registration, processing, storage, 

 viability testing, and regeneration (figure 7-2). 



Registration 



When seeds arrive at a storage facility, pass- 

 port information must be recorded and a num- 

 ber assigned to facilitate recordkeeping. Pass- 

 port data may include information on the origin 

 of the sample, its source (if acquired from 

 another facility), and any pertinent physiolog- 

 ical details that would aid storage. Data of in- 

 terest to potential users, such as disease resis- 

 tance, also may be included. 



The information accumulated may reflect the 

 focus of a particular collection. The Royal Bo- 

 tanic Gardens at Kew, England, requires de- 

 tails on the location and habitat in which a wild 

 plant species was collected, an estimate of the 

 total number of plants represented by the sam- 

 ple, a taxonomic classification, and the loca- 

 tion of a reference herbarium specimen. The 

 more detailed this preliminary information is, 

 the more useful the accession is for crop de- 

 velopment or conservation. 



Collections may receive the accessions of 

 another collection, thus duplicating materials. 

 Although such duplication does provide secu- 

 rity against loss, the number of accessions held 

 by all collections does not reflect duplicates. 

 In barley, for example, the total of more than 

 280,000 accessions in storage is considerably 

 greater than the estimated 50,000 distinct ac- 

 cessions worldwide (70). 



Processing 



Once registered, other data such as estimates 

 of the number of seeds received, viability in 

 terms of percentage of germination, and taxo- 

 nomic identification must be obtained. In addi- 

 tion, seeds may require preparation, like clean- 

 ing and drying for storage. 



Seeds are tested for germinating ability to de- 

 termine if the sample is of high viability or 

 whether it must be planted to produce fresh 

 seed before storing (29,30,31,43). 



To reduce moisture in seeds, procedures 

 using chemical desiccants have been developed 

 and are widely applied (111). Facilities with 

 large amounts of seeds to process, such as the 

 U.S. Plant Introduction Stations or the National 



