At present, the demand for new crop germplasm from farmers in centres of diversity, and from gene banks, is surprisingly modest. But at present the technology of crop breeding is changing rapidly. Is it possible that in the near future these changes will expand the demand for new germplasm?
The answer depends on the balance between countervailing trends. Advances in conventional breeding have increased the scope for incorporating genes from landraces that are distant relatives. Wide crosses have enabled wheat breeders to incorporate genes from other related grasses. This should, on the one hand, raise the demand for the germplasm of such grasses. But it might also reduce the demand for germplasm from closer relatives. Advances in genetic engineering are likely to increase the feasibility of such wide crosses and decrease the time needed to incorporate their effects in new cultivars.
However, genetic engineering is also expanding the sources of genetic change for crops much farther afield. Commercial cotton is now being grown incorporating a gene for pest resistance from Bacillus thuringiensis, and this gene is also being used by breeders of potatoes, tobacco and other crops. A fish gene has been transferred to potatoes to induce cold tolerance. Farmers' crops and their wild relatives are no longer the sole source of valuable genetic material for crop breeders. They have competition from genes found in the whole spectrum of terrestrial life forms. For yield increases and stress tolerance, which often entail combinations of genes, crop breeders are likely to concentrate mainly on their own elite lines as breeding materials, as they have in the past (see Duvick, 1984). The continued search for higher yields is unlikely to have a major effect in the near future on the demand for exotic germplasm.
In fact the supply of potentially useful genes is even wider. They can be synthesized via several methods (Orton, 1988) including irradiation (which produced new barley cultivars), chemically induced mutation, and somaclonal variation induced via in vitro propagation. In addition, transposable elements, which can relocate genes and alter their expression, are another source of genetic variation that might prove to be a fruitful source of genetic improvements.
How these countervailing effects will balance out is still to be seen. Effects may differ in the short and longer runs. But there seems to be no good reason to expect a dramatic change in the profile of utilization presented in the preceding section.
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