Some morphological and physiological features of chrysanthemum under in vitro culture

Chrysanthemum is an ornamental plant native to East Asia, with a wide range of cultivars and forms. Cuttings are the main method of propagation, but clonal micropropagation is now actively used due to a greater efficiency. In order to determine the rate of formation of vegetative organs, we analyzed large-flowered cultivars 'Egiptyanka', 'Antonov', 'Quartet', 'Tango' and small-flowered cultivar 'Kraski Oseni'. The plant samples were collected in April-May 2016. Meristems were used as initial explants. For rhizogenesis induction the microshoots were cultured on MS medium with NAA and IBA. During 18 months of culture 4 transplants were made. Different explants were placed at 24±1°C, 16-h photoperiod under 37.5 μmol m^-2 s^-1. The smallest leaf blades were noticed in 'Kraski Oseni' (0.9×1.0 cm). Under in vitro conditions, 'Antonov' stood out due to its large leaves (1.4×1.2 cm). The leaf blades were thin (102-153 µm). The cover tissues were presented by a single-layer epidermis and adaxial epidermis cells had thickened the cell walls. The shape of the cells was amoeboid. The stomatal apparatus were of the anomocyte type, at the same level with the epidermal cells, and were mainly in open state. Multicellular trichomes (4-cell) and stomata (24-84 stomata mm^-2) were found in a great amount on the abaxial surface of the leaf blades. The leaf mesophyll consisted of 2-3, rarely 4 layers, and the intercellular spaces were large. Only in 'Antonov', 'Kraski Oseni' and 'Egiptyanka' differentiation for palisade and spongy chlorenchyme was noted. The palisade index was 0.38-0.42. Plantlets of those cultivars can be considered completely formed and capable of functioning ex vitro.