Ch. 3— Status of Biological Diversity • 77 



Table 3-5.— Crops Grown or Imported by the 



United States With a Combined Annual Value of 



$100 Million or More (average 1976 to 1980) 



SOURCE: C, Prescolt-Allen and A. Prescott-Allen, The First Resources: Wild Spe- 

 cies in f/7e North American Economy (New Haven, CT. and London: 

 Yale University Press, 1986). 



varieties better suited for production at particu- 

 lar sites; and 2) the increased uniformity of 

 crops, which makes them more vulnerable to 

 pests and pathogens. Of these two, extinction 

 of genes is the greater problem. For annual 

 crops, uniform genetic vulnerability can be 

 quickly corrected as long as a high degree of 

 genetic diversity is maintained for the crop 

 somewhere. Gene extinction, however, cannot 

 be reversed. 



Published information on status and trends 

 of crop diversity usually consists of impressions 

 by plant breeders and others on the loss of cul- 

 tivated varieties or threats to wild relatives of 

 crops, such as: "it may not be long before land- 

 races are irretrievably lost" or "many locally 

 adapted varieties have been replaced by mod- 

 ern varieties" (39). Such reports have been col- 

 lected and evaluated by the International Board 

 on Plant Genetic Resources (IBPGR). IBPGR's 

 information has stimulated conservation action 

 and has helped to determine general collect- 

 ing priorities for protection of genetic re- 

 sources. 



Plant breeders and germplasm collectors gen- 

 erally concur that crop genes have been lost 

 and that losses are still occurring rapidly and 

 widely in many crops (39], in spite of progress 

 with collection and offsite maintenance pro- 

 grams (see ch. 6). Three problem areas include: 



1. crops that have low priority for IBPGR but 

 are of major economic importance to the 

 United States (e.g., grape, alfalfa, lettuce, 

 sunflower, oats, and tobacco); 



2. crops that despite being a high interna- 

 tional priority still lack adequate provision 

 for long-term conservation (including those 

 maintained as living collections rather than 

 as seeds, such as cacao, rubber, coconut, 

 coffee, sugarcane, citrus, banana); and 



3. wild relatives of major crops, which, ex- 

 cept for sugarcane and tomato, are repre- 

 sented in collections by extremely small 

 samples. 



Detailed assessments of the status and trends 

 of genetic diversity are lacking, even for crops 

 whose collection is well advanced, such as rice. 



