Clonal propagation plays a critical integral role in the growth and success of a global multi-billion dollar horticulture industry through a constant supply of healthy stock plants. The supply chain depends on continuously improving the micropropagation process, thus, understanding the physiology of in vitro plants remains a core component. We evaluated the influence of exogenously applied cytokinins (CKs, N6-benzyladenine = BA, isopentenyladenine = iP, meta-topolin = mT, 6-(3-hydroxybenzylamino)-9-(tetrahydropyran-2-yl)purine = mTTHP) in Murashige and Skoog (MS)-supplemented media on organogenic response and accumulation of endogenous CK and indole-3-acetic acid (IAA) metabolites. The highest shoot proliferation (30 shoots/explant) was obtained with 20 μM mT treatment. However, the best quality regenerants were produced in 10 μM mT treatment. Rooting of Amelanchier alnifolia in vitro plantlets was observed at the lowest CK concentrations, with the highest root proliferation (3 roots/explant) in 1 μM mTTHP regenerants. Similar to the organogenic response, high levels of endogenous bioactive CK metabolites (free bases, ribosides, and nucleotides) were detected in mT and mTTHP-derived regenerants. The level of O-glucosides was also comparatively high in these cultures. All CK-treated plants had high levels of endogenous free IAA compared to the control. This may suggest an influence of CKs on biosynthesis of IAA.

Laboratory of Growth Regulators and Department of Chemical Biology and Genetics Centre of the Region Haná for Biotechnological and Agricultural Research Faculty of Science Palacký University and Institute of Experimental Botany AS CR Šlechtitelů 11 CZ 783 71 Olomouc Czech Republic

Ornamental and Fruit Tree Nursery Jan Holub s r o Hvozdečko 7 783 25 Bouzov Czech Republic

Research Centre for Plant Growth and Development School of Life Sciences University of KwaZulu Natal Pietermaritzburg Campus Private Bag X01 Scottsville 3209 South Africa

Research Centre for Plant Growth and Development School of Life Sciences University of KwaZulu Natal Pietermaritzburg Campus Private Bag X01 Scottsville 3209 South Africa; Department of Horticultural Sciences Faculty of Applied Sciences Cape Peninsula University of Technology P O Box 1906 Symphony Way Bellville 7535 Cape Town South Africa

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Applications of Cytokinins in Horticultural Fruit Crops: Trends and Future Prospects