Optimisation of growing conditions for the apple rootstock M26 grown in RITA containers using temporary immersion principle

Abstract

The use of bioreactors may provide an efficient and economic tool for mass clonal propagation of plants if technical problems can be solved. In this paper, we report the results of experiments aimed at optimising conditions for apple rootstock M26 growth in RITA containers using the temporary immersion principle. We tested different types and sizes of explants, different concentrations of plant growth regulators (BAP, kinetin and IBA) in the multiplication and elongation phases, and medium exchange during the shoot elongation period. The results show that the higher concentrations of cytokinins were required during the shoot multiplication phase, while the lower concentrations were better during the shoot elongation phase. Hyperhydricity was increased with increasing concentrations of cytokinins during both shoot multiplication and shoot elongation phases. The best shoot production in terms of shoot number and shoot quality was obtained using 4.4 µmol BAP and 0.5 µmol IBA during the shoot multiplication phase and 1.1 µmol BAP and 0.25 µmol IBA during the shoot elongation phase. Medium exchange twice during the shoot elongation phase resulted in higher shoot production compared with no exchange of the medium. However, it also resulted in increased hyperhydricity. Immersion frequency of 16 times per day gave a higher multiplication rate and longer shoots than 8 times per day. The explant size of 0.5 cm or 1 cm resulted in a significantly higher shoot production rate compared with that of 1.5 cm, but shoot length and hyperhydricity were not affected by the explant size. Shoot cultures from the liquid media rooted normally in the RITA containers with more than 90 % rooting and the rooted plantlets acclimatised well in the greenhouse.