52 * Technologies To Maintain Biological Diversity 



Photo credit: M. Plotkin 



Medicine from nature: Croton sp., l<nown as "sangre 



de grado" in the Peruvian Amazon. This tree produces 



a sap used for a variety of medicinal purposes. 



duce, then the productivity and adaptabiUty of 

 the population will progressively decline. 



In addition, certain populations are better 

 adapted to particular locations than others. For 

 example, chinook, coho, and sockeye salmon 

 from different rivers are genetically distinct; 

 these distinctions reflect differences in the 

 physical and chemical characteristics of the 

 streams in which they originated (69,70). Diver- 

 sity needs to be maintained so that any restock- 

 ing to compensate for overharvesting or habi- 

 tat degradation can use populations that are 

 adapted to the specific environmental con- 

 ditions. 



In agriculture, genetic diversity in the form 

 of readily available genes reduces a crop's vul- 

 nerability to pests and pathogens. Resistance 

 genes can be introduced as long as a high de- 

 gree of genetic diversity is maintained in off- 

 site collections, onsite reserves, and agroeco- 

 systems. U.S. plant breeders keep a substantial 

 supply of diversity in cultivars, parental lines, 

 synthetic populations, and other breeders' stocks 

 ready for use (13,26). 



The genetic variation in domesticated plants 

 and animals and in their wild relatives is the 

 raw material with which breeders increase 

 yields and improve the quality of crops and live- 



stock. Use of genetic resources during this cen- 

 tury has revolutionized agricultural produc- 

 tivity. In the United States from 1930 to 1980, 

 yields per unit area of rice, barley, and soybeans 

 doubled; wheat, cotton, and sugarcane yields 

 more than doubled; fresh-market tomato yields 

 tripled; corn, sorghum, and potato yields more 

 than quadrupled; and processing-tomato yields 

 quintupled (65,92). 



At least half of these increases have been at- 

 tributed to plant breeders' use of genetic diver- 

 sity. The gain due to breeding is estimated to 

 be 1 percent per year for corn, sorghum, wheat, 

 and soybeans, due mainly to improvements in 

 grain-to-straw ratio, standability, drought re- 

 sistance, tolerance of environmental stress, and 



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Ptioto credit: United Nations— M. Tzovaras 



Plant breeders' use of genetic diversity has significantly 

 increased the productivity of crops such as wheat. 



