| Abstract: | A Nicotiana gametosomatic hybrid between N. tabacum and N. glutinosawas studied. It was shown to have a stable somatic chromosomecomplement of 2n=5x=60. Karyotypes and measures of DNA contentshow that there have been no major changes in the parental chromosomenumbers or morphology accompanying hybridization. Forty-eightchromosomes are derived from N. tabacum (2n=4x=48); 12 fromN. glutinosa (2n=2x=24). Homologous pairs of N. tabacum chromosomesusually pair normally at meiosis. Trivalents incorporating aglutinosa chromosome do occur but usually these remain as univalents. The fertility of the hybrid is low but some products of self-pollinationwere obtained. These carry the complete N. tabacum genome witha few glutinosa chromosomes, some of which form supplementarybivalents at meiosis. All derivatives studied were mixoploidbut progressive selfing reduces the extent of abnormality ofmitotic divisions. The study of morphological and developmentaltraits indicates that the addition of even a few chromosomesof N. glutinosa to the N. tabacum complement can modify thetabacum phenotype substantially. There is considerable variationamong the derivatives and scope for fixing desirable qualitiesthrough selection. The presence of only a haploid set of glutinosachromosomes in the original hybrid makes the return to a desirablegenotype more efficient than that achieved through more conventionalbreeding methods. Key words: Nicotiana, gametosomatic hybrid, selfed progeny, cytology |
