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

The effect of in vitro colchicine treatment of sugar beet ovules, afte r 7 days culture, on embryo formation, regeneration and ploidy of rege nerated plants was studied with 5 concentrations of colchicine and 5 d urations of treatment arranged as a 5 x 5 factorial in incomplete bloc ks. The best results were obtained with the shortest duration of treat ment (5 hours) and the highest concentration of colchicine (0.4 %) giv ing 5.0 diploid plants per 100 ovules with 62.1 % of regenerated plant s 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 regenerat ed plants. Toxic effects on embryo formation could be explained by sim ple exponential decay models, toxicity of the drug (decay constant) in creasing linearly with duration of treatment. Duration of treatment ha d no effect on chromosome doubling percentages. The effects of colchic ine concentration on chromosome doubling were explained by an exponent ial saturation model with spontaneous chromosome doubling of 8.1 % and saturation at 51.4 % diploid plants at 0.2 % and higher colchicine co ncentrations. In addition, treatments increased percentages of 4N and 6N plants from 0 % without colchicine to 10 % on average for treated o vules. A response surface model fitted to the total yield of diploid p lants per ovule indicated that shorter durations of treatment and high er colchicine concentration may improve results.