Fišerová H., Vyhnánek T., Staňková Z., Kozák V., Klemš M., Havel L. (2016): Effects of garlic genotype on cloves formation under in vitro conditions. Hort. Sci. (Prague), 43: 142-148.Prior to the transfer of multiplicated garlic plants from in vitro to ex vitro conditions it is necessary to induce the formation of bulbs and to verify the identity of propagated young individuals with their maternal plant. This study deals with effects of exogenous compounds (i.e. paclobutrazol, abscisic acid and ethylene) on formation of bulbs of four garlic cultivars (Lan, Lukan, Emilie, Japo) and on production of ethylene and carbon dioxide (CO 2 ). In the softneck garlic cv. Emilie, the exogenous application of paclobutrazol increased numbers of daughter cloves and production of both ethylene and CO 2 . In the softneck cv. Lukan the formation of cloves was higher after the application of ABA than after the application of paclobutrazol (PP 333). An exogenous application of ethylene inhibited the formation of bulbs. Analyses of DNA polymorphism, performed by means of microsatellite markers, verified the identity of bulbs produced under in vitro conditions with their mother plants. The hardneck cv. Lan differed form softneck cvs Lukan, Emilie and Japo.Keywords: paclobutrazol; abscisic acid; 2-chlorethylphosphonic acid; ethylene; microsatellites In the Czech Republic, the need of garlic production is still very actual because consumers are not interested in products of a dull taste and a short shelf life (i.e. storability) that are imported from abroad. Under climatic conditions of the Czech Republic, garlic (Allium sativum L.), a species belonging to the onion genus Allium, does not produce seeds. Flower stems with bulbils and sterile flowers formed by hardneck garlic develop on plants belonging to the group of softneck garlic cultivars only under extreme conditions. The most important problem of Czech garlic production is to obtain sufficient amounts of virus-free planting material of good quality. This problem can be solved by means of vegetative propagation and sanitation of plants under in vitro conditions on the basis of a good knowledge of physiological growth reactions of individual cultivars -genetic origin, external conditions, potential propagation in vitro, gas production etc.The first studies on in vitro propagation of garlic (Allium) plants were focused on effects of different concentrations of N 6 -benzyladenine (BA) and 1-naphthyl acetic acid (NAA) in the medium on formation of young plants from flower heads and stem base (Novák, Havel 1981). In cloned, vegetatively propagated leek plants, no morphological and cytological changes were observed and it was possible to transfer and cultivate them under in vivo conditions. Another study published by these two authors (Havel, Novák 1988) deals with in vitro propagation and the establishment of garlic primary cultures from root segments of 8 garlic cultivars on the Murashige-Skoog medium con- 142