Abstract. Cultured shoots of Rosa 'Improved Blaze' were used to determine the effects of sucrose and inorganic nitrogen on adventitious root formation. Shoots grown in media containing high sucrose concentrations (146.07-262.93 mM) produced more and longer roots than those grown in media containing 0-87.64 mM sucrose. This response to sucrose was related to the metabolism of sucrose rather than its osmotic properties since the use of mannitol and 3-0-methyl-a-D-glucopyranoside as osmotic substitutes did not reproduce the effect on rooting. The number and length of roots increased when the shoots were grown in media with the nitrogen concentration of the MurashigeSkoog (MS) salt formulation reduced from 60 to 7.5 mM. Neither nitrate (NO-3) nor ammonium (NH~) alone at any of the concentrations tested had the effect on rooting that both had together in the ratio of the MS salt formulation. When the sucrose and nitrogen concentrations were both varied, the greatest rate of root initiation occurred on shoots grown in media with a high sucrose to nitrogen concentration ratio.

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The node position from which axillary buds were isolated from shoots of rose (Rosa hybrida L.) markedly affected their growth and development in culture. Those buds nearest to and furthest from the apex either failed to develop or took the longest time to develop in culture compared to those buds in the middle portion of the stem. Benzylamino purine (BA) at low concentrations (0.03 to 0.3 mg/liter) stimulated the development of the axillary buds of ‘Gold Glow’ but not of ‘Improved Blaze’. A photon flux density (400-700 nm) of 17μE m−2 s−1 for 12 to 24 hours daily was optimum for the stimulation of shoot multiplication, while 66 μE mm−2s−1 for 12 to 24 hr was optimum for root initiation and for subsequent successful transplantation to soil of tissue culture-derived plants. A constant temperature of 21°C resulted in the highest rate of shoot multiplication and root initiation. Plants which initiated roots at 16, 21, or 26° had the highest level of transplant survival. An alteration in the temperature of the 8-hr dark period from 21° did not increase shoot multiplication, although root initiation was enhanced by lowering the night temperature to 11 or 16°. Histological analysis indicated that shoot multiplication of rose shoots occurs through the growth and development of axillary buds. The development of axillary buds is apparently under the repressive influence of the shoot apex, because physical excision of the apex or application to the shoot apex of 2,3,5-triiodobenzoic acid (TIBA) facilitated axillary bud development. Root initiation was affected markedly by the length of time that cultures had been maintained on shoot multiplication medium prior to transfer to rooting medium. This effect may be attributable to the BA in the shoot multiplication medium which may have accumulated in the tissue. If the endogenous cytokinin level is too high, root initiation may be inhibited and if it is too low the shoot undergoes senescence before it becomes cytokinin-autonomous, which occurs after root initiation.