Plant Cell, Tissue and Organ Culture 12:205-211 (1988) © Kluwer Academic Publishers, Dordrecht - Printed in the Netherlands 205 INCREASE OF GENETIC VARIABILI TM BY ASYMMETRIC HYBRIDIZATION AND ISOLATED CHROMOSOME ~RANSFER CELL D. DUDITS Institute of Genetics, Biological Research Center, Academy of Sciences, H-6701Szeged, POB 521, Hungary Hungarian i. INTRODUCTION Barriers to crossability between species considerably limit the use of advantageous genes with diverse origin to improve the nutritional quality and increase the total yield potential of crop plants. As the result of progress in development of plant tissue culture techniques and of molecular and cell genetics parasexual manipulation of plant genome has gained an increasing significance to release new possibilities for genetic recombination and extension of genetic variability. Nowadays there are several major approaches to the introduction of foreign genes into somatic plant cells. The transfer of single isolated genes can be efficiently accomplished by using one of the advanced DNA transformation systems based on Agrobacterium (Schell, 1987) or direct plasmid uptake into protoplasts through chemical and physical treatments (Paszkowski et al, 1984) or with help of microinjection (Reich et al, 1986). In addition to production of transgenic plants (Abel et al, 1986; Hilder et al, 1987) with possible use in breeding programs there is a need to manipulate genetically uncharacterized or multigenic traits. For these purposes the methods of cell fusion or organelle transfer offer an alternative solution. The aim of the present paper is to analyse the available experimental results about genomic constructs of hybrid genotypes after cell fusion and isolated chromosome transfer. As we discussed previously (Dudits et al, 1980; Dudits and Praznovszky, 1985) reduction of somatic incompatibility through induced chromosome elimination can be a basic requirement for production of intergeneric hybrid plants. The successful use of asymmetric cell hybrids for limited alien gene transfer depends on tools to control chromosome elimination and genomic recombination in fusion products. Characterization of the introduced new traits in somatic hybrids and in their sexual progenies can help to outline the potentials of these approaches in plant breeding. 2. SPONTANEOUS AND IRRADIATION INDUCED CHROMOSOME ELIMINATION FROM FUSION PRODUCTS Chromosomal behaviour of two parental genomes in cell hybrids is strongly influenced by phylogenetic distance between the fusion partners. Maintenance of double diploid or amphidiploid chromosome sets was characteristic for several intra- and interspecific somatic cell hybrids with related parents as Nicotiana glauca + N.tabacum (Evans et al, 1980),