Genetic control of chromosomal chimerism found in a regenerate from tobacco callus.

Abstract

A regenerated plant of chromosomally chimeric character was obtained from callus cultures of a variety in Nicotiana tabacum. The chimerism was observed in the progeny plants, at least through three selfed generations. Cytological observations of rooted cuttings from axillary buds or stem tips of this lineage confirmed the chimerism. They were weak in growth vigor and showed low seed-set. The capsules of this line were more variable in size and were usually smaller than those of normal plants. Some were “chimeric” for leaf shape, i.e., a mixing of round and nearly normal leaves was sometimes found within the individual. In F1s resulting from reciprocal crosses between chimeric and normal plants, all were chimeric, except for one plant. Segregation of chimeric vs. stable plants in the F2 and B1 generations can be interpreted to fit for 3:1 and 1:1 ratios, respectively, except for one B1 combination. On the basis of segregation data in F2s and B1s, the mode of inheritance can be explained by assuming that the chimerism is mainly controlled by a simple Mendelian gene, probably induced during tissus culture processes. Another interpretation of the results is also presented. Inheritance of two foliar characters, namely bilateral asymmetry and foliar ratio was also investigated in relation to chromosomal chimerism. The chromosomally unstable line exhibited larger asymmetry indices than the normal line, however, no significant difference was found on foliar ratio between these lines. The differences calculated from the pooled data between chromosomally chimeric and stable plants in one F2 and two B1 lines were significant in bilaterial asymmetry, but not in foliar ratio. The results suggest that bilateral asymmetry of tobacco plants is correlated with the chromosomal chimerism.