Genetic diversity and genetic vulnerability—an appraisal

Abstract

1. Plant germplasm is among the most essential of the world’s natural resources. Its conservation merits far greater attention than it is now receiving. 2. Total genetic diversity does not provide insurance against genetic vulnerability. To be of use to the breeder, sources of genetic diversity must include useful alleles not present in elite populations that carry resistance to pests and other stresses that adversely affect productivity and quality. 3. Breeding programs of the most important crops include only a small percentage of the total germplasm available within each crop. The major reason for this limited use of the stores of germplasm found in gene banks is the lack of evaluation data on such material. Until a gene bank’s accessions are evaluated and documented they will continue to be of limited value to the breeder. 4. The results of a recent survey indicate that the genetic base of several important crops has increased during the past decade. 5. Several criticisms of the Green Revolution (used in the broadest sense) are considered. Introductions of new, improved cultivars do tend to replace indigenous varieties containing potentially useful germplasm. Expanded efforts are needed to rescue such varieties before extinction. Research does not support the contention that modern, genetically-uniform cultivars are necessarily less stable and less dependable than genetically-variable cultivars. 6. With respect to the impacts of a changing seed industry on genetic diversity, it is suggested that these changes will not result in a concentration of fewer varieties used worldwide. The movement of pharmaceutical and chemical companies into the seed industry has occurred too recently to permit an evaluation of the effects of such moves. It will likely result in greater competition which, in turn, will stimulate more breeding and the introduction of a greater number of varieties than have been available in the past. Plant variety protection legislation in the United States has also served to stimulate additional breeding in self-fertilized species and has resulted in an increase in the amount of genetic diversity available to the farmer.