THE SIGNIFICANCE OF INITIAL ADVENTITIOUS ROOTS IN POPLAR CUTTINGS AND THE EFFECT OF CERTAIN FACTORS ON THEIR DEVELOPMENT

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Abstract
In planted cuttings of Populus trichocarpa Torr. and Gray, P. x canadensis Moench 'Regenerata', and P. x canadensis 'Robusta Bachelieri', adventitious roots developed first along the cutting, then later at the basal end. Removal of the first roots, termed initial roots, resulted in decreased shoot growth during the early growth of the cuttings and a smaller root system at the end of the growing season. Mortality occurred only in those cuttings from which all initial roots had been removed. Poplar varieties differed significantly with respect to number, but not length of initial roots produced. In general, the number, length and weight of initial roots increased with the cutting moisture content and with temperature. Number of roots increased with increasing age of parent shoot up to a maximum at 10 months, with no further increase up to 16 months. Cuttings from the base of the shoot produced longer, and in the hybrids, heavier roots than cuttings from the top. At 50% moisture content, basal cuttings produced more roots than top cuttings, but at 100% moisture content, there was no significant difference between the shoot regions. The position in which cuttings were placed exerted a significant effect on the number of roots produced in the hybrids, but not in P. trichocarpa.