Ch. 7— Maintaining Plant Diversity Offsite • 173 



quency of viability monitoring and regenera- 

 tion. However, cryogenic storage is economi- 

 cal for only certain plant species; larger seeds, 

 such as beans, may be stored more economi- 

 cally under mechanical refrigeration (102). 



In vitro cultures may be more economical 

 than extensive field collections, particularly if 

 the cultures are stored cryogenically. However, 

 further research and development is needed on 

 both in vitro culture and cryogenic storage. 



COLLECTING SAMPLES 



Collecting samples involves the development 

 of strategies as well as the actual collection of 

 plants. Developing strategies can be facilitated 

 by analyzing plants already in storage. Ideally, 

 a strategy would provide for the collection of 

 all genetic variants of a species without redun- 

 dancy (37) (box 7-B). 



Strategies 



Considerations of economic or esthetic im- 

 portance, rarity, degree of endangerment, ac- 

 cess, genetic diversity, and similarity to plants 

 already stored offsite can all influence tbe set- 

 ting of strategies. 



For the major agricultural species, collection 

 strategies have been established by consider- 

 ing the data on plants already collected, geo- 

 graphic distribution of crop species, particu- 

 lar needs of breeders, and the economic or 

 social importance of the crop (117). The Inter- 

 national Board for Plant Genetic Resources has 

 established a system of priority ratings to guide 

 collectors: Priority 1 crops are those with most 

 urgent global collection needs; Priorities 2, 3, 

 and 4 indicate descending orders of urgency 

 (51,73). 



Strategies are less clearly established for the 

 collection of most wild species (66). In general, 

 those threatened in their natural environment 

 or of display value have received greater atten- 

 tion (69,112). A formal system for coordinat- 

 ing conservation activities has only recently 

 been established (34,112). Botanic gardens, 

 commercial institutions, and private collections 

 have been growing and propagating rare plants 

 for years but without concern for obtaining a 

 range of genetic diversity (69). Organizations 

 such as the Botanic Gardens Conservation Co- 

 ordinating Body of the International Union for 

 the Conservation of Nature and Natural Re- 



sources (lUCN) and the Center for Plant Con- 

 servation at the Arnold Arboretum of Harvard 

 University are beginning to focus the expertise 

 and resources of botanic gardens, arboretums, 

 and private collectors to improve offsite main- 

 tenance of wild plants. 



Selecting Sites for Collecting 



Studies of the geographic distribution of 

 plants, the experiences of scientists and plant 

 collectors, computer-based models, and re- 



Pholo credit: M O Grady 



Collecting natural rubber {Hevea) In the Amazon forest. 



Natural rubber still has many industrial uses for which 



synthetic rubber cannot be employed. 



