EFFICIENT IN-VITRO CHROMOSOME DOUBLING DURING BETA-VULGARIS OVULE CULTURE

The effect of in vitro colchicine treatment of sugar beet ovules, after 7 days culture, on embryo formation, regeneration and ploidy of regenerated plants was studied with 5 concentrations of colchicine and 5 durations of treatment arranged as a 5 x 5 factorial in incomplete blocks. The best results were obtained with the shortest duration of treatment (5 hours) and the highest concentration of colchicine (0.4 %) giving 5.0 diploid plants per 100 ovules with 62.1 % of regenerated plants being diploid. Statistical analysis revealed that treatment effects could be separated into a toxic effect reducing embryo formation and a chromosome doubling effect affecting percentages of diploid regenerated plants. Toxic effects on embryo formation could be explained by simple exponential decay models, toxicity of the drug (decay constant) increasing linearly with duration of treatment. Duration of treatment had no effect on chromosome doubling percentages. The effects of colchicine concentration on chromosome doubling were explained by an exponential saturation model with spontaneous chromosome doubling of 8.1 % and saturation at 51.4 % diploid plants at 0.2 % and higher colchicine concentrations. In addition, treatments increased percentages of 4N and 6N plants from 0 % without colchicine to 10 % on average for treated ovules. A response surface model fitted to the total yield of diploid plants per ovule indicated that shorter durations of treatment and higher colchicine concentration may improve results.