Chromosomes in somatic hybrids between Nicotiana plumbaginifolia and a monoploid potato

Summary Leaf mesophyll protoplasts of the monohaploid potato (Solanum tuberosum L.) clone H7322 were fused with callus protoplasts of nitrate reductase deficient (NR^–) mutants Cnx 20 and NA 36 of Nicotiana plumbaginifolia. Somatic hybrid lines were selected for nitrate reductase proficiency. All callus lines tested appeared to be stable for the retention of the potato chromosome carrying the compensating NR gene when grown for over 1.5 years in the absence of nitrate. Shoots were regenerated from six different fusion lines of Cnx 20 + H7322 24 months after fusion. Chromosomal analysis in callus cultures revealed that in both fusion combinations 40–120 N. plumbaginifolia chromosomes were present, as were 9–20 potato chromosomes. Cells with 17 potato chromosomes in combination with a relatively small number (31) of N. plumbaginifolia chromosomes were found in one line. Preferential loss of species-specific chromosomes was not observed. Analysis of regenerating tissue from three lines of Cnx 20 + H7322 revealed that after 24 months of culture intra- and intergeneric translocations, fragments and deletions were present. Elimination of the potato and N. plumbaginifolia chromosomes had taken place before and after genome doubling.