In vitro induction of tetraploids in colchicine-treated cocoyam plantlets

Colchicine was applied in liquid B5 medium supplemented with 0.49 mu m N-6( Delta(2)-isopentenyl)adenine to tissue culture derived cocoyam plantlets. T etraploids (4n=52) and octoploid (8n=104) were produced by treating plantle ts 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 mixop loids were of the 2x-4x, 2x-4x-8x and 4x-8x types with 4x cells being domin ant. Non-treated plantlets and plantlets treated with dimethylsulphoxide (D MSO) had typical diploid chromosome counts, 2n=26. Flow cytometric analysis showed a significant increase in relative amounts of DNA in nuclei of colc hicine-treated tissues corresponding to 4C levels and peaks appearred at ex citation channels of 100.05 +/- 4.4. Nuclei of non-treated plantlets had 2C levels of relative DNA amounts, peaks occurring at fluorescence channels o f 52.8 +/- 2.7. Most of the cells of non-treated plantlets were arrested at the G(1) phase (90.5%) with negligible amounts at S (6.9%) and G(2)/M (2.6 %). Colchicine-treated plantlets had relatively lower number of nuclei at G (1) (33.6 or 33.3% for 1.25 mM or 2.50 mM) and significantly higher number of nuclei at G(2) (47.1 or 46.0% for 1.25 mm or 2.5 mm). Non-treated tissue s had significantly lower nuclei at S-phase compared to colchicine-treated plantlets.