Somatic hybridization between Nicotiana rustica and N. tabacum. III. Biochemical, morphological, and cytological analysis of somatic hybrids

The hybrid nature of parasexually produced plants of Nicotiana rustica L. + N. tabacum L. has been verified by biochemical, morphological, and cytological analysis. The isozyme banding patterns for esterase, aspartate aminotransferase, and superoxide dismutase of 10 somatic hybrid lines were compared with the parent species. The banding patterns were complex and for any given enzyme they varied among the hybrid lines. For each enzyme assayed a number of isozyme bands derived from both parental species were found in the hybrids. The aspartate aminotransferase zymogram of the hybrids was particularly interesting consisting of a unique hybrid band and also a dense band which appeared as a result of the presence of both parental bands. Leaf and flower morphology of a further 17 hybrid plant lines was analyzed and found to be generally intermediate with respect to the parents though the variability between lines was great considering the small statistical sample. A heterosis effect for plant vigor and height was observed among one-third of the lines. Self-fertility was low among the hybrid lines with only two yielding viable seeds. Only one hybrid line had the expected chromosome complement of 96; all the others contained less. The chromosome complement of the hybrids was unstable ranging from 2n = 68 to 96 between different lines and also varied among different members of the same line ranging from 2n = 68 to 92. The genetic instability indicated by variable chromosome complements can account for the variability found in the biochemical and morphological analyses.