In vitro plants of the gynogenetic haploid line 86122/560 of gerbera were treated with colchicine or oryzalin dissolved in dimethylsulfoxide, to compare the antimitotic efficiency of these substances. The ploidy level was evaluated by flow cytometry two months after the treatment. Decrement of the multiplication rate was taken into account for the evaluation of the toxic effect of the antimitotic substances. Controls both with and without dimethylsulfoxide maintained the haploid status. At comparable doses, oryzalin proved to be as efficient as colchicine, but slightly less phytotoxic. Longer oryzalin treatments could probably induce the diploidization of a larger number of cells and reduce the problem of chimaeric plants.

The genetic transformation of plants calls for efficient organogenetic methods. Both cytokinins and antibiotics were tested to evaluate shoot regeneration from internodes of in vitro plants of Camellia x williamsii cv Debbie. High regeneration rates were achieved by using thidiazuron, which turned out to be more effective than 6-benzylaminopurine. Up to 96% of explants regenerated when thidiazuron was used, whereas no more than 75% regenerated using 6-benzylaminopurine. The best average number of shoots per regenerant explant was 9.7 and 5.6 regarding respectively thidiazuron and 6-benzylaminopurine. Kanamycin, used in combination with the best performing thidiazuron concentration, completely blocked regeneration at 129 μM. Cefotaxime at 524 μM decreased the regeneration ability, especially when 2 day preculture was applied. The application of genetic transformation protocols as well as the main aims of genetic engineering in ornamental camellias are discussed.

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