In vitro multiplication of Merton I. 793–An apple rootstock suitable for replantation

In vitro shoot multiplication of Merton I. 793, a clonal apple rootstock, was achieved through terminal/axillary bud culture using Murashige and Skoog (MS) basal medium supplemented with 0.5-1.0 mg/L 6-benzyl amino purine (BA) and 0.1 mg/L indole-3-butyric acid (IBA). Time of collection of explants, duration of surface sterilents and growth regulators added in the medium influenced the survival of explants and their bud break. Although, the shoots were multiplied on different concentrations of cytokinins and auxins, improved multiplication was achieved with 0.5 mg/L BA and 0.01 mg/L IBA. Of the three types of explants evaluated for shoot multiplication, shoot tips on elongation were found suitable for rooting whereas, nodal cuttings and cluster of small shoots for further multiplication. Low concentrations of α-naphthyl acetic acid (NAA) was proved to be more effective for rooting as compared to IBA and indole-3-acetic acid (IAA). To overcome profuse callus formation during rooting, activated charcoal was added. In another experiment, auxin was discontinued from the rooting medium after few days, thus, resulting in better rooting frequency (72%). Thirty plantlets of Merton I. 793 were successfully hardened after 7 wks, with around 80% survival rate.