Gene transfers into plants as a natural and experimental phenomenon

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. In plants, 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 a first 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 genes