In vitro induction of tetraploids in colchicine-treated cocoyam plantlets

Colchicine was applied in liquid B5 medium supplemented with 0.49 μm N6(δ2-isopentenyl)adenine to tissue culture derived cocoyam plantlets. Tetraploids (4n=52) and octoploid (8n=104) were produced by treating plantlets with 1.25 mM and 2.50 mM colchicine. Of all the plantlets treated with 1.25 mM or 2.5 mM, 16.7% and 20.0% respectively were mixoploids. These mixoploids were of the 2x-4x, 2x-4x-8x and 4x-8x types with 4x cells being dominant. Non-treated plantlets and plantlets treated with dimethylsulphoxide (DMSO) had typical diploid chromosome counts, 2n=26. Flow cytometric analysis showed a significant increase in relative amounts of DNA in nuclei of colchicine-treated tissues corresponding to 4C levels and peaks appearred at excitation channels of 100.05 ± 4.4. Nuclei of non-treated plantlets had 2C levels of relative DNA amounts, peaks occurring at fluorescence channels of 52.8 ± 2.7. Most of the cells of non-treated plantlets were arrested at the G1 phase (90.5%) with negligible amounts at S (6.9%) and G2/M (2.6%). Colchicine-treated plantlets had relatively lower number of nuclei at G1 (33.6 or 33.3% for 1.25 mM or 2.50 mM) and significantly higher number of nuclei at G2 (47.1 or 46.0% for 1.25 mm or 2.5 mm). Non-treated tissues had significantly lower nuclei at S-phase compared to colchicine-treated plantlets.