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  • Author or Editor: Jeff L. Sibley x
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Auxin solutions prepared with sodium cellulose glycolate (SCG; a thickening agent, also known as sodium carboxymethylcellulose) and applied to stem cuttings using a basal quick-dip extend the duration of exposure of cuttings to the auxin and have previously been shown to increase root number and/or total root length on stem cuttings of certain taxa. In a series of three experiments, 3.75-cm stem sections (representing the bases of stem cuttings) of three ornamental plant taxa were dipped to a depth of 2.5 cm for 1 s in solutions prepared with selected rates of SCG using either deionized water or a 10% dilution of an alcohol-based rooting compound (Dip 'N Grow). Each stem section was weighed before and after being dipped in the solution. Regression equations were determined for each experiment and the rate of SCG providing the maximum ratio of SCG solution weight to stem piece weight was determined by setting the first derivative of the regression equation equal to zero. Maximum adhesion of solution was obtained using SCG at 13.35 to 13.71 g·L−1 with an average rate of 13.5 g·L−1.

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The objective of this study was to determine differences in the bulk anthocyanin content of bark tissue of container-grown red maple (Acer rubrum L. and Acer ×freemanii E. Murray) at two Georgia locations with different environmental conditions. Rooted cuttings and tissue-cultured plantlets of eight cultivars were grown in either Blairsville or Tifton, Ga. [U.S. Dept. of Agriculture (USDA) Hardiness Zones 6b and 8a; American Horticultural Society (AHS) Heat Zones 5 and 8, respectively], from June 1995 until Dec. 1996. Bark tissue from twigs of trees grown in Blairsville was visually redder and contained more total anthocyanin than did that of trees grown in Tifton. Levels of total anthocyanins were higher (P = 0.0007) at Blairsville (0.087 mg·g-1, N = 48) than at Tifton (0.068 mg·g-1, N = 47). At both locations the levels were highest in `Landsburg' (`Firedance'™), followed by `Franksred' (`Red Sunset'™) and `October Glory'. This is the first report to quantify anthocyanin differences in bark tissue of container-grown trees. Cooler nights in Blairsville might have contributed to increased coloration by reducing respiratory losses, thus leaving more carbohydrates available for pigment production.

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In the southeastern United States, inconsistent pine bark (PB) supplies and overabundance of cotton gin by-products warrant investigation about the feasibility of replacing PB with cotton gin compost (CGC) for container horticultural plant production. Most research on the use of composted organic substrates for horticultural plant production has focused on shoot growth responses, so there is a need to document the effect of these substrates on root growth. In 2004, `Blitz' tomato (Lycopersicon esculentum), `Hot Country' lantana (Lantana camara `Hot Country'), and weeping fig (Ficus benjamina) were placed in Horhizotrons to evaluate root growth in 100% PB and three PB:CGC substrates containing, by volume, 60:40 PB:CGC, 40:60 PB:CGC, and 0:100 PB:CGC. Horhizotrons were placed in a greenhouse, and root growth in all substrates was measured for each cultivar. Physical properties (total porosity, water holding capacity, air space, and bulk density) and chemical properties (electrical conductivity and pH) were determined for all substrates. Physical properties of 100% PB were within recommended guidelines and were either within or above recommended ranges for all PB:CGC substrate blends. Chemical properties of all substrates were within or above recommended guidelines. Root growth of all species in substrates containing CGC was similar to or more enhanced than root growth in 100% PB.

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Stem cuttings of golden euonymus (Euonymus japonicus `Aureo-marginatus'), shore juniper (Juniperus conferta `Blue Pacific'), white indian hawthorn (Rhaphiolepis indica `Alba'), and `Red Cascade' miniature rose (Rosa `Red Cascade') were successfully rooted in plugs of a stabilized organic substrate that had been soaked in aqueous solutions of the potassium salt of indole-3-butyric acid (K-IBA) at 0 to 75 mg·L–1 before inserting the cuttings. Cuttings were rooted under intermittent mist in polyethylene-covered greenhouses with rooting periods appropriate for each species. Rooting percentages showed some increase with increasing auxin concentration with juniper cuttings, but were similar among treatments for the other three species. Number of roots per rooted cutting increased with increasing auxin concentration with cuttings of juniper, Indian hawthorn, and rose, and was greatest using around 60 mg·L-1 K-IBA for cuttings of juniper and Indian hawthorn and 30 to 45 mg·L-1 K-IBA for cuttings of rose.

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Traditional propagation courses seldom allow extensive evaluation of the variables required for successful propagation. A series of experiments were designed to give an individual student practical experience in woody plant propagation. Softwood terminal cuttings were taken on five shrub or tree species, dividing each species into separate experiments comparing talc vs. liquid auxin formulations. Selections evaluated included luster leaf holly with treatments of 3000, 8000, and 16,000 ppm K-IBA; hetz holly, crape myrtle, and anise tree with treatments of 1000, 3000, and 8000 ppm K-IBA; and sugar maple with 8000 and 16,000 ppm K-IBA. Budding and seed propagation also were evaluated in sugar maple. In each species, except sugar maple, liquid quick-dip at the highest K-IBA concentration produced the best rooting. The student gained many educational benefits in basic experimental design, evaluation of data collected, and drawing conclusions to findings significant by industry standards. The student also learned and how production cycles have an impact on various methods, development stages of cutting material, and wounding techniques. The practical propagation experience gained was of primary importance thereby further preparing the student for employment in the industry.

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Stem cuttings of Hydrangea paniculata Sieb., Rosa L. `Red Cascade', Salvia leucantha Cav., and Solenostemon scutellarioides (L.) Codd `Roseo' were inserted into six rooting substrates: monolithic slag [(MgFe)2Al4Si5O18], sand, perlite, vermiculite, Fafard 3B, or fine pine bark. Rooting, initial shoot growth, and ease of dislodging substrate particles from root systems upon bare-rooting by shaking and washing cuttings rooted in monolithic slag were compared to cuttings rooted in the five other substrates. Rooting percentage, number of primary roots per rooted cutting, and total root length per rooted cutting for cuttings rooted in monolithic slag were generally similar to the five other substrates. Particles of monolithic slag were dislodged more readily from root systems by shaking than were the other substrates. Gentle washing removed almost all particles of monolithic slag and sand from the root systems of all taxa and removed almost all particles of pine bark from all taxa except S. scutellarioides `Roseo'. Monolithic slag had a bulk density similar to sand, retained less water than the other substrates, and was similar to perlite, vermiculite, and pine bark in particle size distribution. Our studies indicate that monolithic slag, where regionally available, could provide a viable material for producing bare-root cuttings.

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A substrate component (WholeTree) made from loblolly pine (Pinus taeda L.) was evaluated along with starter fertilizer rate in the production of greenhouse-grown petunia (Petunia ×hybrida Vilm. ‘Dreams Purple’) and marigold (Tagetes patula L. ‘Hero Spry’). Loblolly pine from a 12-year-old plantation were harvested at ground level, chipped, and further processed through a hammer mill to pass a 0.64-cm screen. The resulting WholeTree (WT) substrate was used alone or combined with 20% (WTP2) or 50% (WTP5) (by volume) Canadian sphagnum peatmoss and compared with an industry standard peat-lite (PL) mix of 8 peatmoss : 1 vermiculite : 1 perlite (by volume). Substrates were amended with 1.78 kg·m−3 dolomitic lime, 0.59 kg·m−3 gypsum [CaSO4-2(H2O)], 0.44 kg·m−3 Micromax, 1.78 kg·m−3 16N–2.6P–9.9K (3- to 4-month release), and 1.78 kg·m−3 16N–2.6P–10.8K (5- to 6-month release). A 7N–1.3P–8.3K starter fertilizer (SF) was added to each substrate at 0.0, 1.19, 2.37, or 3.56 kg·m−3. Container capacity (CC) was greatest for PL and decreased as the percentage of peatmoss in the substrate decreased with WT having 35% less CC than PL. Conversely, air space (AS) was greatest for the WT and decreased as percentage of peatmoss increased with PL containing 33% less AS than WT. In general, petunia dry weight was greatest for any substrate containing peatmoss with a SF rate of 2.37 kg·m−3 or greater. The exception was that petunia grown in WT at 3.56 kg·m−3 SF had similar dry weight as all other treatments. Marigold dry weight was similar for all substrates where at least 2.37 kg·m−3 SF was used.

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International undergraduate study programs give students an advantage in the job market, broaden their understanding of and experience with other cultures, and allow them to develop professional international contacts. Since 2003, faculty and administrators in the Department of Horticulture at Auburn University have been providing horticultural study tours for faculty and undergraduate and graduate students in horticulture. In 2003 and 2004, undergraduate students and faculty participated in an about 10-day non-credit study tour of gardens in London and southeastern England. In 2005, undergraduate students, a graduate student, and faculty participated in an 8-day non-credit study tour of gardens, horticultural production facilities, and natural ecosystems in Costa Rica. All of these tours in 2003 to 2005 occurred during the break between spring and summer semesters. In 2005, a 6-week study abroad program (1 June to 15 July) was offered at a college in northwestern England. Students received 13 hours of credit for four classes: Landscape Gardening, History of Garden Design, International Agriculture Seminar, and Herbaceous Plant Materials. In addition to class time, trips were arranged each week to regional gardens and retail and production facilities. Plans for 2006 include a week-long non-credit study tour of gardens and production areas in The Netherlands during the break between spring and summer semesters, a 2-week study tour of government, university, and agricultural production areas in Hungary in July (offered in conjunction with the College of Agriculture), and a repeat offering of the study abroad program in England.

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Performance evaluation of red maple (Acer rubrum L.) selections in the southeastern U.S. was initiated in November 1988. Seven cultivars, `Autumn Blaze', `Autumn Flame', `Morgan', `Northwood', `October Glory', `Franksred' (Red Sunset TM) and `Schlesingeri', from tissue culture and a group of seedlings obtained from a single source were container grown for 18 months prior to field planting in March 1990. All plants have received drip irrigation in the field. Since field planting, 'Autumn Flame', and 'Autumn Blaze' exhibit the greatest growth rate based on annual height and caliper data. 'Schlesingeri' and 'Northwood' had the least growth. Gas-exchange measurements taken in June 1992, showed 'Schlesingeri' and 'Northwood' to have the greatest photosynthetic activity and transpirational water loss while 'October Glory' and 'Frankred' had the least.

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Net photosynthesis (Pn), stomatal conductance (Cs), transpiration (Ts), and water use efficiency (WUE) were determined with a LICOR 6250 Portable Photosynthesis System for four cultivars of Acer rubrum L. under light intensities ranging from 300 to 1950 μmol·m-2·sec-1 photosynthetically active radiation (PAR). As PAR increased, there was a linear relationship for Pn, Cs, and Ts for the cultivars `Franksred' (Red Sunset TM) and `October Glory'. In contrast, the cultivars `Schlesingeri' and `Northwood' had quadratic relationships for Pn and Cs as PAR increased. Ts was quadratic for `Schlesingeri' and had a linear relationship for `Northwood.' WUE was quadratic for each of the four cultivars.

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