Summary — The type of carbohydrate used in the medium influenced the proliferation of Malus Jork 9. The microcuttings obtained showed marked differences in rooting ability. During proliferation, sorbitol (0.176 M)

Root formation in shoot cuttings of soybean (Glycine max L. `Williams'), mungbean (Phaseolus aureas Mdlbg.), English ivy (Hedera helix L.), and apple (Malus ×domestica Borkh. `Jork 9') was stimulated by dithiothreitol and reduced glutathione in the presence and absence of auxin (IAA) shock. In soybean, in the absence of auxin, root formation was stimulated to about the same extent by glutathione alone as with auxin alone. The roots induced by thiol compounds were longer than roots induced by auxin shock and were completely normal in appearance. Roots produced with auxin shock alone were short and exhibited characteristic auxin-induced deformations. With a combination treatment of auxin shock and thiol compounds, roots were more numerous than with either alone, somewhat longer than with auxin alone, and exhibited fewer of the usual deformations characteristic of roots grown in the presence of external auxins. The thiol compounds also were beneficial for rooting Malus shoots propagated from callus in vitro. The thiol compounds were most beneficial with older cuttings where auxin shock was often insufficient to obtain roots. In shoots where rooting was stimulated by thiol agents, shoots grew more rapidly than in those where rooting was induced by auxin shock alone. These findings suggest a use for thiol compounds alone or in combination with auxin shock to induce differentiation of root primordia as well as for stimulation of root growth. Chemical name used: indole-3-acetic acid (IAA).

Shoot microcuttings of Malus domestica cv. Jork 9, Malus domestica cv. Cepiland, Mandevilla (Dipladenia) sanderi, and Daphne odora cv. variegata were induced to root by the addition of 0.1-1 mM dithiothreitol following an auxin (indole-3-acetic acid) treatment to initiate root formation. The most difficult to root, Malus domestica cv. Cepiland, required higher dithiothreitol concentrations to achieve optimum rooting than did the less difficult to root, Malus domestica cv. Jork 9, Mandevilla sanderi, or Daphne odora variegata. The roots induced by the combination of dithiothreitol and auxin treatment were approximately twofold longer and more robust than those induced with auxin treatment alone. The combination treatment of auxin and dithiothreitol has the potential to be of practical importance in root initiation in difficult-to-root cuttings of both woody and herbaceous horticultural varieties.

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