Adventitious Rooting and Physiology of Stem Cuttings of Loblolly Pine

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Title: Adventitious Rooting and Physiology of Stem Cuttings of Loblolly Pine
Author: LeBude, Anthony Vincent
Advisors: Farrell C. Wise, Committee Member
Barry Goldfarb, Committee Co-Chair
John Frampton, Committee Member
Frank A. Blazich, Committee Co-Chair
Abstract: Vegetative propagation by stem cuttings can be used to multiply improved seedlings of timber species before deployment for reforestation. Before full scale deployment of rooted stem cuttings can be accomplished on an operational level, however, various obstacles need to be overcome. Among these obstacles are development of rooted cutting production systems and effective control of the rooting environment to stimulate adventitious root formation. Therefore, two separate series of experiments were conducted to develop protocols for clonal propagation of loblolly pine (Pinus taeda L.) by stem cuttings. The first series of experiments were conducted to test the efficacy of two containerized production systems on rooting percentage, root system morphology, and first year field growth of rooted stem cuttings of loblolly pine. The second series of experiments focused on the effect of the rooting environment on adventitious root formation to define a propagation protocol with broad application that stimulates rooting among several rooting environments. In the first series of experiments, three studies were conducted to test adventitious rooting of juvenile hardwood (dormant) or softwood (succulent) stem cuttings of six unrelated full-sib families of loblolly pine in various sizes of Jiffy® Forestry Peat Pellets or Ray Leach Conetainers™ and the subsequent effect on first year field growth after outplanting. Controls in all experiments were Ray Leach Super Cells filled with a medium of 2 peat : 3 perlite (v/v). After adventitious rooting in the greenhouse and 12 months of field growth, all plants, with the exception of plants produced in one Jiffy pellet size, were shorter than the controls and had less root dry weight (DW) and shoot DW. Results suggest that preplant root DW is an important predictor of first year field performance. Therefore, cuttings rooted in pellets may need to be transplanted to a nursery bed for further root growth and development prior to field planting. Rigid plastic containers remain a viable production system because cuttings rooted consistently, had large root mass, and plants were of commercial size after 1 year of field growth. In the second series of experiments, six studies were conducted. Four studies investigated the influence of cutting water potential (Ψcut) on rooting of juvenile dormant and succulent stem cuttings of loblolly pine propagated under varying substrate water potentials (Ψsub) and volumes of mist application (mist levels). In the first two studies, mist level and Ψsub contributed to the Ψcut of nonrooted stem cuttings. In the second two studies, when Ψsub was held constant across various mist treatments, mist level contributed strongly to Ψcut. In the first two studies, Ψsub affected rooting percentage when mist was suboptimal or excessive; otherwise, mist had a stronger effect than Ψsub on rooting percentage. For all four studies, cuttings rooted best when experiencing moderate water deficits (- 0.5 to - 1.2 MPa) during the period of adventitious root formation. Results demonstrate that monitoring the physiological status of stem cuttings during adventitious rooting can provide important information for controlling the rooting environment. The final two studies of the second series of experiments investigated the relationships between mist application, vapor pressure deficit (VPD), Ψcut, and rooting percentage of dormant or succulent stem cuttings of loblolly pine. In addition, net photosynthesis at ambient conditions (Aambient) and stomatal conductance (gs) of succulent stem cuttings were measured during adventitious root formation to determine their relationship to rooting percentage. Dormant stem cuttings rooted ≥ 80% when mean daily VPD between 1000 and 1800 HR ranged from 0.60 to 0.85 kPa. Although rooting percentage was related to Ψcut and gs, and Aambient was related to Ψcut and gs, rooting percentage of succulent stem cuttings was not related to Aambient. Using VPD as a control mechanism for mist application during adventitious rooting of stem cuttings of loblolly pine might increase rooting percentages across a variety of rooting environments.
Date: 2005-04-13
Degree: PhD
Discipline: Horticultural Science

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