Asymmetric hybridization in Nicotiana by "gamma fusion" and progeny analysis of self-fertile hybrids.

Mesophyll protoplasts of the nitrate-reductase (NR)-deficient Nicotiana plumbaginifolia mutant, "Nia26", were fused with γ-irradiated mesophyll protoplasts of Nicotiana sylvestris, V-42. Hybrid selection was based on complementation of NR deficiency by transfer of the donor NR gene to N. plumbaginifolia. Regenerated hybrids had different numbers of donor chromosomes in a tetraploid background of N. plumbaginifolia. The transfer and expression of different isozymes from the donor were also observed. Six self-fertile regenerants were obtained from 21 independently isolated cell colonies. Progeny analyses revealed: (1) the linkage of NR and shikimate dehydrogenase (ShDh); (2) a stabilization of the transmission rate of NR; and (3) the obtainment of mono- and disomic addition lines in the first and second progeny of the original regenerants. Southern hybridization analyses demonstrated unequivocally the presence of the NR gene from the donor partner in progeny plants.