Intrageneric asymmetric hybrids between Nicotiana plumbaginifolia and Nicotiana sylvestris obtained by ‘gamma-fusion’

Asymmetric nuclear hybrids have been obtained by fusion between protoplasts from nitrate reductase deficient mutants of Nicotiana plumbaginifolia and gamma-irradiated protoplasts of Nicotiana sylvestris (dose 500 and 1000 Gy). Fusion products were recovered at a frequency of 0.13%–0.29% following selection for genetic complementation of nitrate reductase function. The somatic segregation of genetic traits as a consequence of radiation damage and in vitro passage has been demonstrated by studying the expression and transfer of biochemical traits from the donor, e.g. expression of the enzyme lysopine dehydrogenase and several isozymes; transfer of ribosomal 25S DNA. A dose effect relation could also be observed by correlating the regeneration efficiency and the relative expression of these markers with the retention of donor chromosomes and fragements in regenerated plants. The asymmetric hybrids were only partially self-fertile and progeny has usually been obtained by back-cross. This particular somatic fusion combination between compatible species allowed us to isolate large numbers of asymmetric hybrids and to study the elimination of donor genetic material as a function of radiation effects and in vitro passage.