Ch. 7— Maintaining Plant Diversity Offsite • 185 



Photo credit: International Board for Plant Genetic Resources 



Current practice for conserving short-lived, clonally propagated materials is to grow individual accessions as field 



collections every year as with these potatoes. However, this approach is expensive in terms of space and labor, and 



it has the disadvantage of possible losses due to pests and diseases and to genetic change. 



many species, particularly for crossing mate- 

 rials that flower at different times (107,108). A 

 population of pollen grains collected from ge- 

 netically different individuals would contain 

 the nuclear genes; cytoplasmic (nonnuclear) 

 genetic factors would not be transmitted, how- 

 ever, because these are not inherited through 

 the pollen (108). 



Pollen can be separated into types that are 

 tolerant or intolerant of drying (81,107,108). 

 Tolerant types store best when dried and main- 

 tained at low temperatures, much like ortho- 

 dox seeds. But the pollen of many species does 

 not survive low moisture or freezing tempera- 

 tures. Some intolerant types, notably maize, 

 have been successfully preserved in liquid ni- 

 trogen, but data on success are sparse (3,107, 

 108). 



Considerable information is still needed on 

 stability and longevity of storing pollen, how- 

 ever, before its use in storage will be possible 

 (108). Pollen is undesirable as the sole propagule 

 for base collection storage because whole plants 

 cannot generally be obtained from it (81,108). 

 In addition, pollen storage does not circumvent 

 potential plant health problems because some 

 pathogens are pollen-borne. 



Biotechnology 



Biotechnology provides additional opportu- 

 nities to improve offsite maintenance of plants. 

 Of particular relevance are in vitro cultures of 

 plants that are now maintained in field collec- 

 tions. And developments in genetic engineer- 

 ing may make the storage of isolated DNA prac- 

 tical in the future. 



