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  • Author or Editor: A. N. Roberts x
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Abstract

The Mugo or Swiss mountain pine is one of the most popular evergreen shrubs for modem landscaping. Mugo pines include the type species (sometimes referred to as var. mugo or var. mughus) and 3 additional geographical varieties pumilio (Haenke) Zenari, rostrata (Ant.) Gord., and rotunda (Link) Gord. (1, 8). The most desirable dwarf forms for landscape use are derived from p. mugo var. pumilio. The other 2 botanical varieties are usually of arboreal size.

Open Access
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Abstract

Recent interest in the production of Rhododendrons as potted plants has raised many questions concerning propagation, dormancy, flower initiation, and general patterns of growth and development. Cathey (1) has shown that general growth habit may be altered to give a more compact plant through the use of Phosphon or by B-nine. He found further that flower initiation could be stimulated after the production of 4-5 flushes of growth instead of the normal 8-9 flushes required under natural conditions, thus making this plant useful as a potted plant. Myhre (3) showed that large applications of phosphate fertilizer increased the number of terminal apices initiating flowers in ‘Cynthia’. In 1920, work in the Netherlands by Luyten and Versluys (2) indicated that leaf and flower initiation occurred early in the growth cycle, May 31 to June 8.

Open Access

Georgia plume, Elliottia racemosa (Ericaceae), is a small tree endemic only to the state of Georgia, where it is listed as a threatened species. Information about genetic relatedness is critical for establishing approaches for safeguarding, reintroduction, and conservation of this rare species. The genetic relationships among and within selected georgia plume populations were evaluated using random amplified polymorphic DNA (RAPD) in conjunction with site visits at which time a census and GPS survey were conducted. Populations ranged from those containing eight to over 1000 individuals with most populations containing few plants (less than 50 individuals). With one exception, small populations with less than 50 individuals had more genetic similarity than populations with greater numbers of plants. Two protected populations containing large numbers of individuals were sampled extensively. Genetic similarity of individuals was not associated with plant proximity within a population. The small number of individuals and geographic isolation characteristic of many populations were associated with high within-population genetic similarity. Conservation priorities should be given to preserving as many different populations as possible to retain the genetic diversity of the species. Whether the narrow genetic variation found in some populations may be contributing to lack of sexual reproduction in the wild is an area for further study.

Free access

Abstract

Succulent branch terminal cuttings of Douglas-fir [Pseudotsuga menziesii (Mirb) Franco] placed horizontally (adaxial side up) curved slightly. Cuttings placed vertically, horizontally (adaxial side down), or on a horizontal clinostat exhibited significant adaxial-convex curvature. The response is regulated, in part, by substances exported from the needles and terminal bud. Gibberellic acid (GA3), (2-chloro-ethyl)phosphoric acid (ethephon), amino-ethoxyvinylglycine (AVG), indolebutyric acid (IBA), triiodobenzoic acid (TIBA), and 6-benzylamino purine (BA) failed to affect the curvature of vertically placed shoots.

Open Access

Abstract

A study of shoot apex size and initiatory activity in August-harvested ‘Ace’ bulbs following 0, 6, and 18 weeks vernalization at 40°F showed negetative correlations between leaf and flower number and length of vernalization treatment, and between apex size and this cold treatment. Growth acceleration as reflected in earlier shoot emergence, internode elongation and rapid leaf unfolding was evident following 6 weeks’ 40°F storage, but prolonged (18 weeks) treatment drastically reduced subsequently initiatory activity and rate of leaf unfolding.

Open Access

Abstract

Inflorescence slices of tall bearded iris (Iris sp.) regenerated callus in vitro on a modified Murashige-Skoog high salt medium supplemented with 2.5 mg/liter napthaleneacetic acid (NAA) and 0.5 mg/liter kinetin. Callus pieces transferred to light initiated plantlets at their periphery and produced fuU-sized, true-to-type flowering plants when transplanted to soil.

Open Access

Several microsprinkler treatments were tested on 5-year-old satsuma mandarin orange (Citrus unshiu Marc.) trees to compare survivability of trunks and scaffold limbs in severe freezes. Three damaging freeze events occurred during winter, with two in 1995–96 and one in 1996–97. Air temperature dropped to –9.4, –5.6, and –6.7 °C, respectively. Almost 90% of the foliage was dead on the control plants after the first freezing event and 98% after the second. A single microsprinkler 1.6 m high in the canopy delivering 90.8 L·h–1 reduced injury; only 54% of the canopy was dead after the first freeze and 71% after the second. There was slightly more shoot-tip dieback on the plants in the microsprinkler treatments than on the control plants after the first two freezes. The amount of limb breakage by ice was minor. The third freeze killed 34% of the canopy in the control plants, but only 26% in the plants in the microsprinkler treatments. Use of microsprinklers increased yield in 1996, but yield for all treatments was very low. Yield for all treatments fully recovered in 1997, averaging 153 kg/tree. Although no death of scaffold limbs or trunks occurred, these results demonstrate that microsprinkler irrigation reduces damage to foliage and increases yield somewhat in severe freezes.

Free access

Rhizosphere pH preferences vary for species and can dramatically influence root growth rates. Research was conducted to determine the effect of root zone pH on the root growth of BuxusmicrophyllaSieb. & Zucc. `Green Beauty' (boxwood) and KalmialatifoliaL. `Olympic Wedding' (mountain laurel). Boxwood plants removed from 3.8-L containers and mountain laurel plants removed from 19-L containers were situated in the center of separate Horhizotrons™. The key design feature of the Horhizotron is four wedge-shaped quadrants (filled with substrate) that extend away from the root ball. Each quadrant is constructed from glass panes that allow the measurement of roots along the glass as they grow out from the root ball into the substrate. For this experiment, each quadrant surrounding a plant was filled with a pine bark substrate amended per m3 (yd3) with 0.9 kg Micromax (Scotts-Sierra, Marysville, Ohio) and 0, 1.2, 2.4, or 3.6 kg dolomitic limestone. All plants received 50 g of 15N–3.9P–9.8K Osmocote Plus (Scotts-Sierra), distributed evenly over the surface of the root ball and all quadrants. Plants were grown from May to Aug. 2003 in a greenhouse. Root lengths were measured about once per week throughout the experiment. Root length increased linearly over time for all species in all substrates. Rate of root growth of boxwood was highest in pine bark amended with 3.6 kg·m3 lime and lowest in unamended pine bark. Rate of root growth of mountain laurel was lowest in pine bark amended with 3.6 kg·m3 lime. Results support the preference of mountain laurel and boxwood for acidic and alkaline soil pH environments, respectively.

Free access