SELECTION OF ATRAZINE-RESISTANT TOBACCO VARIANTS FROM PHOTOMIXOTROPHIC CULTURES

Photomixotrophic cell cultures of Nicotiana tabacum L. (cv. Wisconsin 38) were established and used to select atrazine resistant variants. Thirty-seven plants were regenerated and rooted in the presence of atrazine from clonal cell lines selected for resistance. Variants showed variability in pollen viability, leaf shape and size, plant height, seed set and floral structure. Most morphological abnormalities were associated with chromosomal abnormalities and an increased frequency of chromosomal abnormalities were associated with higher atrazine concentrations in the selection media. Herbicide binding to chloroplast thylakoid membranes, oxygen evolution, leaf disk bleaching and leaf disk callusing were used as assays to determine resistance levels to atrazine in selected variants. The first two methods appeared to be the more accurate means of determining atrazine resistance. Some variability may be attributed to differences in physiological maturity, somaclonal variation, or to the sorting out of resistant and susceptible chloroplast populations.