Management of chimera through direct shoot regeneration from florets of chrysanthemum (Chrysanthemum morifolium Ramat.)

The main bottleneck of mutation induction in vegetatively propagated ornamentals is the development of chimera. Ephemeral small sectors apparent on petals cannot generally be recovered as solid mutant shoots. An efficient technique has been standardized in the present experiment for direct shoot regeneration from individual florets of chrysanthemum (Chrysanthemum morifolium Ramat.) cv. Colchi Bahar. The efficiency of direct shoot regeneration was tested on 16 media based on MS basal medium containing sucrose, agar and different concentrations and combinations of BAP and NAA. The regenerative potential varied with the developmental stages of the flower head. The highest percentage of shoot formation and most shoots per responding explant were observed on florets taken from stage II flower heads. Direct shoot formation was confirmed by scanning electron microscopy and histological observations. The technique has been tested on 16 other cultivars in the medium containing 0.2 mg l(-1) NAA and 1 mg l(1) BAP. Gamma ray of 1.5 and 2.0 krad induced yellow and white floret colour sectors in 'Maghi' (original colour-mauve) have been established in pure form using this technique. The regenerated plants were rooted in vitro and successfully transferred to soil where they grew vigorously and flowered true to the floret colour type.