Meetings of the Royal Botanical Society of The Netherlands

Epigenetic variation interferes with vegetative propagation in vitro. especially when the callus phase has to be passed. Ornamental Kalanchoe species show fasciation and aberrant phyllotaxis. The role of plant growth regulators (PGRs) in this form of epigenetic instability was analysed. In the vegetative propagation from leaf discs of Kalanchoe hlossfeldiana Poelln. both auxin and cytokinin are required. The measure ofinstability increases at increasing concentrations of PGRs, especially cytokinin. Lowest instability occurs at low concentrations of such mild regulators as indoleacetic acid (IAA) and zeatin. Cytokinin may induce vitrification which is reduced by low concentrations of auxin.