Factors that determine shoot viability and root development during in vitro adaptation and propagation of silver birch (Betula pendula Roth)

Abstract

Background. Micropropagation of silver birch (Betula pendula Roth) is used to obtain healthy plant material for high-value plantations. The aim of this study was to evaluate the first steps of birch explant introduction and maintenance in vitro in order to make practical suggestions about the influence of these first steps on further micropropagation success. Materials and methods. Of the seven studied birch genotypes, one had been cultured in vitro for two years at the time of experiments, while six were newly planted in vitro from shoot segments disinfected after either one or two weeks of storage of collected branches. The explants were placed in glass culture tubes either on a hormone-free or cytokinin (6-benzylaminopurine)-supplemented medium. Results. A shorter branch storage time (one week instead of two) was better for the viability of explants, while external cytokinin, if used during the very first subculture in vitro, had largely a negative impact. Among the tested birch genotypes, 52BPL171 had the highest rate of viable explants and was followed in this respect by 01BPL115 which, however, contrasted strongly to the former because of its ability to maintain a green shoot apex alongside a green stem on the control medium. After 12 months in vitro, only genotype 01BPL115 was characterized by regular shoot growth and a well-developed root system. Conclusions. The green shoot apex on the control medium and, also, maintenance of viability on the medium with external cytokinin were found to be most helpful characteristics of birch explants during the first subculture, early recognition of those genotypes that would be most promising for obtaining multiple rooting shoots in vitro