Root initiation and elongation in Douglas-fir, Pseudotsuga menziesii (Mirb.) franco, stem cuttings as related to bud and cambial activity Public Deposited

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  • The relation of bud and cambial activity to root initiation and elongation in Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) stem cuttings was studied through two successive growth cycles. Stem cuttings of current season's growth were taken periodically from field-grown Douglas-fir trees to determine: (1) origin and development of root initials; and (2) controlling factors in bud and cambial activity and subsequent rooting in this species. Growth chambers were used to control photoperiod, air temperature, and relative humidity, and propagation benches and portable trays were employed to control the temperature of the rooting medium. Anatomical studies showed that callus originates principally from the vascular cambium, but phloem and xylem parenchyma may also contribute. Differentiation within callus led to the formation of spirally oriented root initials having no connection with the main vascular system. Continuous cell division, differentiation, and subsequent distal elongation of root initials gave rise to root primordia having complete vascular connections with the stem axis. Once root primordia initiated, elongation occurred within 15 to a maximum of 30 days. There was no apparent difference in origin of adventitious roots in cuttings taken at various stages of shoot development. Long photoperiods (18 hr) exerted a profound influence on bud and cambial activity and enhanced rooting over that of short photoperiods (9 hr). This response to photpperiod was modified by stage of shoot development and rooting medium temperature. LD enhancement of rooting was most pronounced before and during bud dormancy, but following bud dormancy cuttings rooted equally well under SD. Cuttings rooted significantly better under 26° (12.95%) and 18°C (11.91%) rooting medium temperatures than under 10°C (1.13%). The cambium of Douglas-fir showed no endogenous dormancy, and cell division in cambium was not a limiting factor in rooting. Auxin treatment significantly increased rootability during pre- and post-dormancy. During true dormancy, auxin treatment alone was not effective in stimulating rooting, and LD or cold treatment was required. Chilling requirement for rooting was considerably less than that for breaking bud dormancy. Cuttings with good callus often failed to root, but many cuttings with only fair callus showed root initiation and elongation, suggesting that root initiation in Douglas-fir is not directly related to the extent of callus formation, but rather to a hormonal balance necessary for differentiation within callus. There was no relationship of cambial activity and cutting rootability to the presence or absence of buds, probably indicating that leaves alone are capable of supplying the growth substances needed for cambial activity and root initiation in Douglas-fir.
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