In vitro multiplication of semi-dwarfing pear rootstock 'Pyrodwarf' in relation to cytokinin types

The most important aspect of successful micropropagation, among other in vitro factors, is to use the optimal types and concentrations of plant growth regulators. With the aim of optimization of in vitro multiplication of pear rootstock 'Pyrodwarf' the effects of different cytokinins including benzyladenine (BA), isopentenyl adenine (2iP), kinetin (KIN) and thidiazuron (TDZ) have been studied at concentrations of 0.2, 0.4, 1, 2 and 3 mg L-1, singly and combined with auxine, indole-3-butyric acid (IBA) at concentrations of 0.1, 0.5 and 1 mg L-1. Murashige and Skoog (1962) was the basic medium used in all combinations. The following multiplication parameters were monitored: multiplication index, length of axial and lateral shoots. The highest multiplication index was obtained on medium with 1 mg L-1 BA and 0.1 mg L-1 IBA, hovewer, the highest length of axial and lateral shoots was obtained on media also with 1 mg L-1 BA without and with 0.5 mg L-1 IBA, respectively. Generally, very poor multiplication was achieved on media with 2iP, KIN and TDZ whereas in many utilized combinations of low concentration of 2iP and KIN with IBA, and particularly in those with KIN rhyzogenesis was induced. Obtained results suggest that the choice of cytokinins for the phase of multiplication of ` Pyrodwarf' rootstock is limited to BA. KIN and 2iP in smaller concentration could be used for regeneration of sturdy and long shoots, especially for elongation phase, but also for rooting phase.