Ch. 7— Maintaining Plant Diversity Offsite • 177 



60). Plants destined for offsite collections, par- 

 ticularly those from centers of diversity, can 

 present particular quarantine concerns. These 

 centers possess not only considerable crop 

 diversity but also widely adapted crop pests and 

 pathogens. An area where coffee and the dis- 

 ease coffee-rust coexist, for example, would be 

 a likely place to obtain plants with rust resis- 

 tance genes, but it could also have pathogens 

 that have adapted to coffee plants (60). 



The presence of most exotic pests can be de- 

 termined by inspection or by treatment of plants 

 upon entry, but some imported plants may be 

 detained while tested for obscure pathogens. 

 Such testing requires well-equipped labora- 

 tories and personnel as well as considerable 

 time. This last constraint— 5 or more years for 

 the detection of certain viruses and virus-like 

 organisms in woody plants— can profoundly af- 

 fect importation of some plants (60). 



Quarantine and Plant Importation 



Establishing quarantine policies and prac- 

 tices for a particular plant species depends on 

 both knowledge of its risk of carrying pests or 

 pathogens and availability of technologies to 

 detect such pathogens (table 7-1). Most plant 

 species, when imported according to regula- 

 tions (e.g., clean and free of soil, and subject 

 to inspection at an authorized port of entry), 

 are considered unlikely to be carrying harm- 

 ful organisms and thus to be of low risk (60). 



Some agricultural crops, such as rice, sor- 

 ghum, or sugarcane and their related wild spe- 

 cies, require greater attention because they 

 might contain pathogens not easily detected by 

 current technologies. 



Certain agricultural plants or plant parts used 

 for vegetative propagation (e.g., sugarcane 

 stems or potato tubers) represent the greatest 

 risk to agriculture because they may be infected 

 with undetected pathogens (60). The U.S. De- 

 partment of Agriculture (USDA) allows small 

 quantities of these plants to beimported for sci- 

 entific use only. Permits typically require that 

 plants be grown under the supervision of a 

 knowledgeable specialist and may require diag- 

 nostic testing for pathogens as well as special- 



ized growing practices (60). Once plants have 

 cleared safeguard restrictions, they may be dis- 

 tributed to the general public. 



In the United States, some plants (e.g., ap- 

 ples, pears, and potatoes) are held at one of the 

 Agricultural Research Service's Plant Protec- 

 tion and Quarantine facilities until they are con- 

 sidered free of any pests or pathogens (60). 

 Plants in this group face the most constraints 

 because the hazards associated with importing 

 them are highest (60). These plants may be held 

 for several years after their original impor- 

 tation. 



In developing countries, plant quarantine sys- 

 tems may lack scientific expertise, facilities, or 

 appropriate governmental infrastructures to 

 support them (14). Therefore, they depend heav- 

 ily on such regulatory constraints as import re- 

 fusal, lengthy quarantine, or treatment for pests 

 or pathogens. These restrictions can result in 

 considerable delay in importation of plants to 

 facilities in these areas. 



Safeguards for Reducing Risic in 

 Imported Cermpiasm 



A number of actions and regulations, either 

 at the place of origin or at the port of entry, 

 reduce the risks associated with plant impor- 

 tation. 



Inspection, certification, testing, or treatment 

 of plants before export can reduce potential 

 quarantine delays (60). Most plants require lit- 

 tle more than inspection to move quickly through 

 quarantine. In vitro plantlet cultures can, in 

 some cases, be imported with fewer restrictions 

 than the plants from which they originate. Such 

 cultures, though, are not considered free of dis- 

 ease without diagnostic testing (60). 



Upon entry, plants likely to contain patho- 

 gens can be tested with a variety of technol- 

 ogies (table 7-2) (59,60). However, procedures 

 vary in reliability and in the resources they re- 

 quire. Indexing, which uses highly sensitive in- 

 dicator plants, is the most reliable and widely 

 used method, but it requires considerable green- 

 house space to maintain the plants necessary 

 for this test (60). Serologic methods that use an- 



