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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.
Twenty open-pollinated families from a virginia pine (Pinus virginiana) seed orchard in South Carolina were planted and managed as Christmas trees at three sites. Retail value and related traits were assessed once the tests reached marketable size (4 years in the field). All traits assessed (except survival) proved to 1) be under a moderate degree of genetic control (family mean heritability = 0.68 for retail value) and 2) have a large range among open-pollinated family means ($11.42/tree to $22.00/tree, retail value) suggesting that they will response well to the traditional tree improvement approach of selection, breeding and testing. The retail value of the best five families tested averaged an increase of $3.47/tree or 20.7% more than the average. At a 6 × 6 ft (1.8 m) spacing [1,210 trees/acre (2,990 trees/ha)], these families would produce an increase in revenue of almost $4,200/acre ($10,387/ha). Much of this increase in value is a result of reducing the cull rate from 14.5% to 8.1%. Survival, height, crown density and straightness of these five families also exceeded the average of the 20 families tested.
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.
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.
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.
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%).
The Top-Stop Nipper (TSN), a four-bladed, hand-held tool developed for reducing leader growth of Christmas trees, was used as a wounding technique to reduce leader growth of Fraser fir (Abies fraseri). A regression model, based on an apical bud volume index (average bud diameter squared × length), was used to predict the number of nips to apply to each leader to yield a target length of 25 to 36 cm. Treatments included control trees (0 nips) and one to seven nips per leader. Nips were applied in May at budbreak. In an earlier study, increasing the number of nips decreased leader elongation when randomly applied to trees without regard to the size of the apical bud. In this study, when the number of nips increased with increasing bud volume index, leader growth was similar among all TSN treatments. Bud density (per unit length) on the 2006 leader increased with the number of nips applied to the 2005 leader. Results might be useful for growers who want to produce dense trees with minimal shearing or for growers who choose to leave a longer leader to produce a more open, “European-style” tree during a shorter rotation time.
The Top-Stop Nipper (TSN), a four-bladed, hand-held tool used to reduce leader growth in Christmas trees, was evaluated on fraser fir (Abies fraseri). The TSN placed incisions (nips) on the previous year's leader to reduce the amount of photosynthate transported to the developing leader. Treatments consisted of a control (zero nips), and one, two, three, or four nips at each of three stages of leader elongation (pre-budbreak, 2–3 cm, and 6–9 cm). The TSN significantly reduced leader elongation. The percentage of leaders that were within the target range of 8 to 14 inches (20.3–35.6 cm) increased from 18% for the control (no nips) to 46% with four nips. The TSN, when combined with traditional knife shearing or growth regulator treatments, might offer a method to produce dense trees with minimal shearing or to leave longer leaders to produce a more open “European-style” tree during a shorter rotation time.
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.
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.