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

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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 3 selfed generations. Cytological observations of rooted cutting 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 F1 resulting from reciprocal crosses between chimeric and normal plants, all were chimeric, except for 1 plant. Segregation of chimeric vs. stable plants in the F2 and B1 [backcross] generation can be interpreted to fit for 3:1 and 1:1 ratios, respectively, except for 1 B1 combination. On the basis of segregation data in F2 and B1, the mode of inheritance can be explained by assuming that the chimerism is mainly controlled by a simple Mendelian gene, probably induced during tissue culture processes. Another interpretation of the results is also presented. Inheritance of 2 foliar characters, i.e., 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 1 F2 and 2 B1 lines were significant in bilateral asymmetry, but not in foliar ratio. Bilateral asymmetry of tobacco plants is correlated with chromosomal chimerism.