Somatic hybridization between potato and Nicotiana plumbaginifolia : 2. Karyotypic modification and segregation of genetic markers in hybrid suspension cultures and sublines.

Several hybrid callus lines were produced through somatic hybridization between the diploid transformed Solanum tuberosum plant clone 413 (2n = 2x = 24) and a diploid wild-type plant clone of Nicotiana plumbaginifolia (2n = 2x = 20). The hybrid callus lines with subdiploid numbers of potato chromosomes were studied for karyotypic evolution as well as for segregation of the transformation marker characters (i.e. hormone autotrophy, opine synthesis, kanamycin resistance and β-glucuronidase activity). Initially, these hybrids (cultured in kanamycin-containing medium) expressed all of the transformation characters. Six callus lines were selected for the establishment of cell suspension cultures; two of these were also used to initiate sublines, one from single cells of a suspension culture, and the other from callus-derived protoplasts. The cell suspension cultures and the sublines were cultured in kanamycin-free medium. After prolonged culture, karyotypic analysis of the various cell suspension lines revealed independent evolution of both parental genomes. Out of the six suspension lines, four showed a considerably reduced number of potato chromosomes as compared to the original hybrid callus lines, whereas the karyotypes of the individual sublines generally reflected the karyotypic diversity of the original cultures. The fate of the marker characters in various suspension cultures and sublines revealed independent segregation of the markers of TL-DNA (hormone autotrophy) and vector T-DNA (kanamycin resistance and β-glucuronidase activity). Loss of the TR-DNA marker (opine synthesis) was observed only in combination with the simultaneous loss of the TL-DNA marker and the vector T-DNA markers. The results on segregation patterns of marker characters are discussed in the light of specific chromosome loss in the hybrid lines and gene linkage relationships.