The rooting ability of shoots raised 'in vitro' from the apple rootstock A2 in juvenile and in adult growth phase

The apple rootstock A2 can be readily propagated in vitro both in the juvenile and in the adult growth phase. Shoots were produced by meristem tip culture from the apple rootstock A2 in different growth phases. The influence of growth phases and different concentrations of PG and IBA was investigated as to rooting percentage, survival percentage, number of roots per rooted shoot, root length, shoot length and formation of callus. IBA at 15 μ M without PG gave a significantly lower rooting percentage than 5 and 10 μ M IBA. PG together with IBA stimulated rooting, the optimum concentrations of PG being, however, not the same for the different growth phases. For the adult growth phase, 10^?4 M PG promoted rooting, whereas 10^?3 M PG markedly inhibited rooting. In the juvenile growth phases, both 10^?4 and 10^?3 M PG stimulated rooting. PG at 10^?4 M also increased the number of roots. The longest roots were obtained at 10^?3 M PG and 5 μ M IBA. PG at 10^?3 M reduced callus formation at all IBA concentrations used. Neither shoot length nor root length influenced the survival percentage.