Chrysanthemum improvement through tissue culture

The use of two in vitro techniques for Chrysanthemum improvement were studied. Firstly, the direction and extent of somaclonal variation was observed using different explants from cultivars with a range of flower shape and colour. Secondly, an attempt was made to produce chimaeras from mixed calluses. Tissue culture methods were developed for callus induction and shoot regeneration from 6 cultivars of Chrysanthemum morifolium and for C. carinaturn (Syn. C. tricolour), C. parthenium (Pyrethrum) and Aster novi-belqii (Michaelmas daisy) which were included in the chimaera work. Flower colour changes were seen among regenerated plants from red, pink and bronze but not from yellow and white cultivars. The direction of colour change was similar to that recorded from spontaneous mutation. Colour change variants were most frequent in plants regenerated from stem (internodal) or petal explants and least from bud explants. All cultivars showed variants in flower shape amongst regenerated plants. The yellow-flowered cultivars showed the greatest range of types of flower shape, variation in shape was less in the bronze, pink, red and white cultivars. The most distinctive variant types of flower shape were the single, quill and pompon types. The explant types giving the greatest variation in flower shapes were buds or petals. Overall, the proportion of normal true-to-type flowers obtained was highest using bud cultures. This could be because in bud cultures some buds retain their structure despite the development of callus, or because new shoots are produced much faster from bud callus than from petal or stem callus. The most successful method for inducing callus fusion was to place fresh explants in contact with each other side-by-side on the medium. Isozyme analysis was used to screen for chimaeric plants, combinations of parent' types being chosen for their distinctively different isozyme patterns. No regenerated plants showed the isozyme pattern of more than one 'parent', but some somaclonal variants in banding patterns of isozymes were obtained