New plants and new plant products by direct gene transfer

The main limitations of conventional plant breeding are the length of time required to produce new, useful varieties and the relatively small gene pool available for sexual crossings. The length of time can be reduced by employing haploid tissue cultures and plants: elimination of undesirable phenotypes and selection of genetic variants is simplified, and the diploid state can be restored, providing the breeder with suitable material for further crossings. Somatic hybridization of plant cells is another step to enlarge the available gene pool: Protoplasts from sexually incompatible plants are fused to form a new genetic unit which contains the genomes of both parent plants. The direct introduction of genes as DNA molecules with the help of gene vectors represents a system of minimal interference with existing, stable genomes. With dicotyledonous plants, the Ti-plasmid system is available for direct transfer of genes, and improve­ment of crop plants can be expected in the near future. Gene vectors for monocotyledonous plants and preferably also for chloroplasts and mitochondria need to be developed. The chief limitation for pro­gress in genetic engineering is insufficient know­ledge on structure, function, and regulation of plant genes on the one hand and of the biochemistry of agriculturally important traits on the other hand