Plant protoplasts of several horticultural and crop species can now be readily regenerated into plants. There are now available several opportunities for their use in the manipulation of genetic systems in plant breeding. Protoplast cloning has recently been shown to produce additional genetic variation in potatoes; the possibility is examined for protoplast cloning of seed producing crop species for new genetic variation. Fusion of protoplasts of different species is now providing an additional method of hybridization; sexually incompatible species can be hybridized and horticulturally useful hybrids are now being produced. Many possibilities exist for hybridization assessments, both nuclear and cytoplasmic, between various crop species; however, the extent to which these wider hybridizations will produce useful genetic variation is not yet clear, and in many instances plant regeneration from these cultured cell hybrids is not yet possible. Plant protoplasts are also providing an opportunity for the transfer of genes between different species. This may be by fusion with an irradiated protoplast system, or by direct transformation. Transfer of genes by using
Agrobacterium
plasmid as a vector system appears promising, and fusions with wild-type protoplasts will ensure the regeneration of non-tumorous plants.
