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  • Author or Editor: W. Todd Watson x
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Three spineless phenotypes of Acacia wrightii G. Bentham ex A. Gray were identified with aesthetic landscape potential. Experiments in seed, cutting, grafting, and tissue culture propagation were undertaken to perpetuate this desired spineless phenotype. Germination percentages for mechanically scarified seeds ranged from 33% to 94%, however yield of spineless seedlings was low (0% to 34%). Sulfuric acid scarification for 10, 20, 30, or 60 minutes hastened and unified germination compared to nontreated seeds by 7 to 8 days. Vegetative propagation was successful for softwood cuttings. Rooting measures increased with auxin (2:1 indole butyric acid to naphthalene acetic acid) concentrations from 0 to 15000 mg·L–1, with maximum rooting percentage (70%), root number (9.2), and root length (12.4 cm) per softwood cutting at 15000 mg·L–1 auxin 8 weeks after treatment. Rooting was not successful for semi-hardwood or hardwood cuttings. Whip-and-tongue or T-bud grafting was not successful. Tissue culture of shoots from in vitro germinated seedlings indicated that shoot proliferation was greatest in Murashige and Skoog (MS) medium with 15 μm zeatin. The number of shoots that rooted in vitro increased with increasing concentrations of indole-3-butyric acid from 0 to 25 μm.

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In previous studies, baldcypress [Taxodium distichum (L.) Rich.] clones were selected for improved field tolerance to alkaline soils, drought, foliar or soil salinity exposure, and for ornamental traits. Objectives of the current research were to 1) determine the clonal responses to potassium salt of indole-3-butyric acid (K-IBA) across seasonal developmental stages of cuttings; and 2) to determine whether rooting and callus percentages and rooted cutting quality (root number, length, and mass) would be sufficient for commercial production should these clones be released to industry. Cuttings were taken from 24 clones at three distinct stages of stem maturity (softwood, semihardwood, and hardwood). Three concentrations of K-IBA were tested [0, 7,500, and 15,000 mg·L−1 (0, 31.1, 62.2 mm, respectively)] on each clone at each stage. Rooting percentages ranged from ≈94% (clone MX1MC33) at the softwood stage to 0% for several clones at the hardwood stage. Some clones such as MX5MC17 rooted at statistically similar percentages in the softwood and semihardwood stages (88% and 83%, respectively). Clone EP3DC16 rooted at low levels (less than 20%) in all stages. Significant (P ≤ 0.05) interactions occurred between growth stage and clone in some cases. Clone EP8DC14 rooted at 59% at the softwood stage but only 37% at the semihardwood stage. Root number and length exhibited three-way interactions (P ≤ 0.05) among clone, developmental stage, and K-IBA concentration. Mean total root length ranged from 2 cm per cutting on semihardwood cuttings of MX2MC31 treated with no growth regulator to 81 cm per cutting on softwood cuttings of TX8DC38 treated with 7500 mg·L−1 K-IBA. Mean root length varied from 2 cm for several clones at the semihardwood stage to 11 cm for softwood cuttings of MX2MC31 treated with 15,000 mg·L−1 K-IBA. The greatest rooting percentages across K-IBA concentrations were typically at the softwood stage. Cuttings treated with either 7,500 or 15,000 mg·L−1 K-IBA rooted at the greatest percentages across stem maturity stages. No clone rooted well in the hardwood stage. The high concentration of K-IBA (15,000 mg·L−1) sometimes induced basal stem damage.

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In previous studies, baldcypress [Taxodium distichum (L.) Rich.] clones were selected for tolerance to high pH soils, drought and salt exposures, and ornamental characteristics. The objective of the current research was to determine the treatment combinations that yielded optimum root quantity (percentage) and rooted cutting quality (root number, length, dry mass, and shoot dry mass) on vegetative cuttings for a representative clone. Cuttings were treated with factorial combinations of one of four potassium salt of indole-3-butyric acid (K-IBA) concentrations [0, 5,000, 10,000, 15,000 mg·L−1 (0, 20.72, 41.44, 62.16 mm, respectively)], wounded or not wounded (1-cm long basal incision), and rooted in one of three substrates (100% perlite, 100% peatmoss, or 50% perlite:50% peatmoss). Data indicated a tradeoff between potential rooting quantity and root quality measurements in response to different substrates. Although rooting percentages were affected by substrates only at P ≤ 0.10 (53% in 100% perlite versus 36% in 100% peatmoss), there were highly significant (P ≤ 0.0001) differences in rooted cutting potential among substrates as measured by the percentage of cuttings with basal callus. Cuttings placed in 100% perlite callused at 85%, whereas cuttings placed in 100% peatmoss callused at ≈53%. The 100% peatmoss treatment, however, yielded cuttings with significantly greater root quality for all measurements, except root number per cutting. Wounding cuttings proved to have deleterious effects on root quality measurements. Total root length was ≈14.5 cm for non-wounded cuttings and ≈10.8 cm for wounded cuttings. Increasing K-IBA concentrations did not significantly (P ≤ 0.05) affect rooting or callus percentages but did significantly affect root dry mass, total root length, and average root length per cutting. Total root length increased from 10.8 cm at 0 mg·L−1 K-IBA to 16 cm at 15,000 mg·L−1 K-IBA. Mean root number per cutting increased from ≈1.6 with wounded cuttings planted in 100% peatmoss to ≈3.1 with non-wounded cuttings planted in 100% perlite. Results suggested that high-quality softwood baldcypress cuttings should not be wounded, should be treated with 15,000 mg·L−1 K-IBA, and grown in a substrate with intermediate water-holding capacity to achieve an acceptable balance between rooting percentage and rooted cutting quality objectives.

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Seedlings from 13 open-pollinated families of Taxodium distichum (L.) L.C. Richard from the gulf coast, central and south Texas, and Mexico were grown in a nursery in College Station, Texas. Forty seedlings per family were measured on three dates during the production cycle; 99, 109, and 133 days after sowing in Spring and Summer 2004. A two-step cluster analysis based on height and trunk diameter created 3 clusters of families. Cluster 1 had a mean height of 32 cm and a mean trunk diameter of 3.3 mm. Cluster 2 had a mean height of 33 cm and a mean trunk diameter of 3.4 mm. Cluster 3 had a mean height of 43 cm and a mean trunk diameter of 4.1 mm. Although clusters 1 and 2 are statistically significantly different, practically there is little difference between the two. The families from Mexico and central Texas were all in cluster 1 or 2 and the families collected from the gulf coast were all placed in cluster 3, with the exception of a single family from Biloxi, Miss., which was placed in cluster 1. Analysis of covariance revealed that family membership and days after sowing were both highly significant, as well as an interaction between family and days, for height. Families from Mexico and central and south Texas were 10 to 15 cm shorter than the families from the gulf coast, with the exception of the single family from Biloxi, Miss. Only days and the interaction between family and days were significant for trunk diameter. A pattern similar to the cluster analysis means was seen among the families for trunk diameter in the analysis of covariance.

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Tree transplanting practices influence plant survival, establishment, and subsequent landscape value. However, transplanting practices vary substantially within the horticultural industry. Of particular importance is the location of the root collar relative to soil grade at transplant. The objective of this study was to determine the effects of factorial combinations of planting depths, root collar at grade or 7.6 cm either above or below grade, and soil amendments on container-grown (11 L) Quercus virginiana Mill. Soil treatments included a tilled native soil (heavy clay loam, Zack Series, Zack-urban land complex, fine, montmorillonitic, thermic, udic paleustalfs), native soils amended with 7.6 cm of coarse blasting sand or peat that were then tilled to a depth of 23 cm, or raised beds containing 20 cm of sandy loam soil (Silawa fine sandy loam, siliceous, thermic, ultic haplustalfs). A significant (P ≤ 0.05) block by soil amendment interaction occurred for photosynthetic activity. Incorporation of peat significantly decreased the bulk density of the native soil. Planting depth had no significant effect on photosynthetic activity or stem xylem water potential at 3 months after transplant. Soil water potentials did not statistically differ among treatments.

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Planting depth during container production may influence plant growth, establishment, and subsequent landscape value. A lack of knowledge about the effects of common transplanting practices may lead to suboptimal performance of planted landscape trees. Planting depth, i.e., location of the root collar relative to soil grade, is of particular concern for posttransplant tree growth both when transplanted to larger containers during production and after transplanting into the landscape. It is unknown whether negative effects of poor planting practices are compounded during the production phases and affect subsequent landscape establishment. This study investigated effects of planting depth during two successive phases of container production (10.8 L and 36.6 L) and eventual landscape establishment using lacebark elm (Ulmus parvifolia Jacq.). Tree growth was greater when planted at grade during the initial container (10.8 L) production phase and was reduced when planted 5 cm below grade. In the second container production phase (36.6 L), trees planted above grade had reduced growth compared with trees planted at grade or below grade. For landscape establishment, transplanting at grade to slightly below or above grade produced trees with greater height on average when compared with planting below grade or substantially above grade, whereas there was no effect on trunk diameter. Correlations between initial growth and final growth in the field suggested that substantial deviations of the original root to shoot transition from at-grade planting was more of a factor in initial establishment of lacebark elm than the up-canning practices associated with planting depth during container production.

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