Optimisation of the media for in vitro shoot proliferation and root induction in three new cold-hardy and dwarfing or semi-dwarfing clonal apple rootstocks

Abstract

SummaryRootstocks have been used to influence precocity, tree size, fruit quality, yield efficiency, and mineral uptake, and to withstand adverse environmental conditions in many fruit tree species. However, some apple (Malus × domestica Borkh.) rootstocks with excellent horticultural characteristics are difficult to propagate by conventional methods. Tissue culture can be used to propagate new rootstocks developed from breeding programmes for use in experimental trials and for the rapid large-scale production of rootstocks for commercial production. The aim of this study was to propagate several newly-introduced apple rootstocks which were cold-hardy and dwarfing, or semi-dwarfing, and to improve their rooting ability through tissue culture. Major factors that influenced shoot proliferation and rooting were examined and optimal media were developed for the efficient micropropagation and rooting of in vitro shoots of the apple rootstocks ‘GM256’, ‘Budagovsky 71-3-150’, and ‘Budagovsky 60-160’. The optimum proliferation medium for all three apple rootstocks was Quoirin and Lepoivre (QL) medium containing 0.5 mg l–1 6-benzylaminopurine (BAP) and 0.05 mg l–1 indole-3-butyric acid (IBA). Shoot explants of ‘Budagovsky 60-160’ on 1.0× Murashige and Skoog (MS) proliferation medium, 0.75× MS, or 0.5× MS showed shoot tip necrosis and hyperhydricity. Rooting percentages and numbers of roots per plantlet were highest using dark culture for all three rootstocks. The highest rooting percentages for all three rootstocks were obtained on 0.5× QL medium containing 0.5 mg l–1 IBA and 2% (w/v) sucrose, but the rooting percentage of ‘Budagovsky 60-160’ was not significantly different between 0.25× MS and 0.5× QL rooting media.