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Orthotropic shoots (tips of primary axes) from 3-year-old Fraser fir seedlings [Abies fraseri (Pursh) Poir.] were grafted onto rootstocks of Fraser fir, Korean fir (A. koreana Wils.), momi fir (A. firma Sieb. & Zucc.), Nordmann fir (A. nordmanniana (Steven) Spach.), Turkish fir (A. bornmuelleriana Mattf.), and West Virginia balsam fir from Canaan Valley (Canaan fir) [A. balsamea (L.) Mill. var. phanerolepis Fern.]. Firstyear survival in the greenhouse was 92% to 98% except for momi fir (83%). The percentage of grafted plants with orthotropic shoots was 92% to 98%, except for Korean (81%) and momi fir (86%). Plants were subsequently established in replicated field experiments on three sites in the piedmont and mountains of North Carolina. In general, leader elongation of grafted Fraser fir scions was greater than leader growth on nongrafted transplants, including Fraser fir. Differences in survival appear to reflect interspecific variation in resistance to phytophthora root rot and/or tolerance of warm environments. Grafting may offer the potential to grow Abies Christmas trees on previously unsuitable sites, or to reclaim or continue using sites already seriously impacted by root rot.

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Seventeen-month-old seedlings from three fraser fir (Abies fraseri [Pursh] Poir.) seed sources (Mount Mitchell, Richland Balsam and Roan Mountain) were inoculated in an outdoor lath house with five genotypes of Phytophthora cinnamomi Rands. After 122 days, overall mortality was 90.5% with significant (p ≤ 0.07) differences among seed sources. The Mount Mitchell source had lower mortality (83.2%) than the Roan Mountain source (95.8%), while the Richland Balsam source (92.5%) was intermediate. Mortality curves were developed using nonlinear regression (Richards' function). Due to a significant seed source × inoculum genotype interaction (p ≤ 0.0001), equations were developed for each combination of seed source and inoculum genotype. Results suggest that while the overall frequency of resistance in fraser fir is low, seed sources differ in their frequency of resistance and that more than one resistance gene may be present. Survivors from this or similar inoculations could be cloned via grafting or rooted cuttings for further resistance testing and/or grafted into a Phytophthora-resistant fraser fir seed orchard.

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This study tested the effects of cutting length and auxin (NAA) concentration on adventitious root formation in softwood stem cuttings from mature eastern hemlock, Tsuga canadensis (L.) Carr., and carolina hemlock, T. caroliniana Engelm. Overall rooting percentage (41%) and percent mortality (22%) were higher for eastern hemlock compared with carolina hemlock (10% rooting and 13% mortality). Rooting percentage of each species responded differently to varying auxin concentrations (0, 1, 2, 4, 8 mm NAA). Maximum rooting (56%) for eastern hemlock occurred at 0 mm NAA; then decreased with increasing auxin concentration. Carolina hemlock rooting percentage increased from the control to a maximum (16%) at 1 mm NAA; then decreased with increasing auxin concentration. For both species, the lowest mortality occurred at the same auxin concentration as maximum rooting. The highest rates of mortality coincided with the same concentrations as the lowest rooting percentages. At all auxin concentrations, eastern hemlock had a higher number of roots and greater total root length relative to carolina hemlock. Mortality among 6-cm stem cuttings was twice that observed for 3-cm cuttings of both species. However, 6-cm cuttings of eastern hemlock that did form adventitious roots had more roots and longer total root length compared with 3-cm cuttings. Chemical name used: 1-naphthalenacetic acid.

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A series of open-pollinated progeny tests of Fraser fir [Abies fraseri (Pursh) Poir.] was analyzed to determine natural variation among six geographic seed sources and to estimate genetic parameters for traits important in Christmas tree production. Highly significant differences were found among seed sources and families within sources (P ≤ 0.0001) for height after 4 years in the field. The individual-tree within-population heritability values for the traits measured in Year 4 ranged from 0 to 0.44, with height having the highest heritability, overall tree quality having a heritability of 0.14, and bud and branching traits having varying heritabilities. Heritability values for height at age 4 varied greatly among the six sources, from 0.15 for the Black Mountains to 0.67 for the Great Smoky Mountains. Highly significant seed source × site interactions as well as family within source × site interactions existed for height. Stability variance analysis, after removing the environmental heterogeneity, showed significant instability across the test sites for two of the six seed sources for height after 4 years, and some rank changes occurred. The high heritability values for height indicate that economically important genetic gains can be made in Fraser fir for Christmas tree production because of the importance of height in determining Christmas tree value.

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Grafting fraser fir [Abies fraseri (Pursh) Poir.] scions onto rootstocks of turkish fir (Abies bornmuelleriana Mattf.) is a strategy used by some Christmas tree growers in the southern Appalachian Mountains of North Carolina to reduce losses by phytophthora root rot caused by Phytophthora cinnamomi Rands. This study compared the traditional time of grafting (April) with eight summer/early fall grafting dates from mid-July through mid-October. Shade and irrigation treatments were also superimposed on the grafting dates. To ensure optimal grafting success, grafting should be performed in the late winter/early spring (April) when scions are dormant and the rootstocks are becoming active. April graft success was 95% but when grafting fresh scions in summer/fall, graft success decreased from 52% in July to 0% in October. Shade improved summer graft success (52% with, 38% without). Irrigation did not significantly affect graft success or subsequent growth. In a supplemental storage study, grafting of stored scion material in summer/early fall was not successful (less than 1%).

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Two methods of application, the Danish Easy Roller and the German Sprühsystem, were tested to evaluate the effectiveness of naphthaleneacetic acid (NAA) at reducing leader growth (tips of primary axes) of fraser fir [Abies fraseri (Pursh) Poir.] Christmas trees. A commercial product, Sucker-Stopper RTU (1.15% ethyl 1-NAA), was applied to leaders at concentrations of 0 to 500 mL·L−1 when leaders were 8 to 15 cm long. As the concentration increased, leader elongation decreased. The Easy Roller reduced leader growth the most, but leader mortality was unacceptable at concentrations 20 mL·L−1 or greater. Although less effective than the Easy Roller, the Sprühsystem caused negligible mortality of leaders. Applying 40 mL·L−1 with the Easy Roller yielded ≈50% of leaders with target lengths of 20 to 36 cm with little mortality. The Sprühsystem gave similar results at 250 mL·L−1. NAA might be useful for producing dense trees with minimal shearing or for producing more natural, open trees during shorter rotations.

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A series of open-pollinated progeny tests of Fraser fir [Abies fraseri (Pursh) Poir.] was analyzed to determine genetic variation of spring frost damage to the terminal leader and lateral branches after a late season frost in May of the third year in the field. The level of spring frost damage was also compared with bud flush dates that had been measured in the nursery before field planting. Seed sources differed significantly for lateral branch frost damage, and families within source differed significantly for both terminal leader and lateral branch frost damage. Greater terminal and lateral frost damage were significantly associated with greater height for all years. As expected, parent elevation was negatively associated with progeny height. Less lateral frost damage was also associated with later terminal and lateral bud flush dates in the nursery. In addition, higher parent elevation was associated with later lateral bud flush dates of progeny in the nursery. Terminal and lateral bud flush dates in the nursery showed high individual tree within-population heritability values of 0.85 and 0.73, respectively. Similar heritability values for the frost damage measurements were low, 0.045 for terminal leader damage and 0.14 for lateral branch damage. Many of the fast-growing families quickly made up for any loss of height from frost damage so that frost damage should not greatly affect the rotation length.

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Two experiments were conducted during which juvenile hardwood or softwood stem cuttings of loblolly pine (Pinus taeda L.) were rooted under six mist regimes in a polyethylene-covered greenhouse to investigate the effect of mist level on vapor pressure deficit (VPD) and cutting water potential (Ψcut), and to determine the relationships between these variables and rooting percentage. In addition, net photosynthesis at ambient conditions (Aambient) and stomatal conductance (gs) were measured in stem cuttings during adventitious root formation to determine their relationship to rooting percentage. Hardwood 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 Aambient was related to Ψcut, rooting percentage of softwood stem cuttings was not related to Aambient of stem cuttings. 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.

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Two experiments were conducted to develop a protocol for rooting stem cuttings from 3-, 5-, and 7-year-old fraser fir [Abies fraseri (Pursh) Poir.] Christmas trees. The first experiment tested the effect of stumping treatments and tree age on shoot production and subsequent adventitious rooting. One auxin concentration [4 mm indole-3-butyric acid (IBA)] and a nonauxin control were tested. Stock plants were stumped to the first whorl (trees in the field 3 and 5 years) or the first, third, and fifth whorls (trees in the field 7 years). Intact (nonstumped) controls were also included for each age. The second experiment was designed to create a quantitative description of the effects that crown (foliage and above ground branches of a tree) position have on the rooting of stem cuttings collected from stumped and nonstumped trees. The exact position was determined by measuring the distance from the stem, height from the ground, and the degrees from north. Crown positions were recorded as cuttings were collected and then cuttings were tested for rooting response. The rooting traits assessed in both experiments included rooting percentage, percent mortality, number of primary roots, total root length, root symmetry, and root angle. In the first experiment, rooting percentage, primary root production, and total root length increased as the age of the stock plant decreased and the severity of the stumping treatment increased. Auxin treatment significantly increased rooting percentage, root production, root lengths, and root symmetry while decreasing mortality. Overall, the highest rooting percentages (51%) and the greatest number of primary roots (8.1) occurred when 3-year-old stock plants were stumped to the first whorl and treated the cuttings with 4 mm IBA. The greatest total root lengths (335 mm) occurred in cuttings from the 3-year-old stock plants. In the second experiment, rooting percentage was significantly affected by the position from which the cuttings were collected. Cuttings collected lower in the crown and closer to the main stem rooted more frequently than cuttings collected from the outer and upper crown.

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Success and subsequent growth of fraser fir [Abies fraseri (Pursh) Poir.] cleft grafts were studied in relation to origin and type of scion material in the tree crown. First- and second-order shoots (current-year) were collected from five zones in the crown, ranging from top to bottom, and grafted to 5-year-old fraser fir transplants in April. Success rates were similar for first- and second-order scions, whereas budbreak and subsequent growth were best for first-order scions. In general, results were best for first-order scions taken from the upper crown. Plagiotropism of grafts was similar for all crown zones and shoot types.

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