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Abstract
The effects of various combinations of naphthaleneacetic acid (NAA), gibberellic acid (GA), and benzyladenine (BA) at 5 or 50 ppm of each and temperature (22 and 25°C) on root initiation in Salix viminalis, L. cuttings were studied. Highly significant influences of temperature, exogenous growth regulators, and temperature-growth regulator interactions on root initiation were demonstrated. Root formation generally was stimulated by increasing temperature from 22 to 25°. NAA stimulated root formation markedly and its effects were further enhanced for at least 10 days by increasing temperature from 22 to 25°. In contrast to NAA, both GA and BA inhibited root initiation. The inhibitory effect of GA was greater at 25 than at 22°; BA had the greater depressive effect at 22°. Addition of GA or BA, or both, to NAA generally reduced the stimulation of root formation by NAA. As temperature increased toward an optimum for root initiation the balance of endogenous growth regulators and possible cofactors may have changed to bring out the stimulatory effects of auxins over the inhibitory influences of cytokinins and gibberellins.