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  • Author or Editor: Jianjun Chen x
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Adenium obesum (Forssk.), Roem. & Schult., commonly known as desert rose, is a high-value, container-grown ornamental plant produced worldwide for its bright floral display and striking sculptural caudex. Little scientific-based information exists regarding the effect of light intensity and nutritional levels on Adenium growth and flowering. In this study, A. obesum ‘Red’ and ‘Ice Pink’ were grown under full sun [with a measured maximum photosynthetically active radiation (PAR) of 1850 μmol·m−2·s−1], 30% shade (1255 μmol·m−2·s−1), or 50% shade (943 μmol·m−2·s−1) in 1.25-L pots top-dressed with controlled-release fertilizer Nutricote® Plus (18N–2.6P–6.6K) at rates to provide 0.4, 0.9, or 1.4 g of nitrogen (N) per pot. Canopy height and width, flower number, and visual quality ratings (based on plant size and form, foliage color, and flowering) were highest after 16 weeks of growth for both cultivars when fertilized with 1.4 g of N per pot. A 30% shade level resulted in plants with the highest flower numbers and quality ratings. Plants grown at 50% shade had the greatest canopy heights and widths, but flower numbers and quality ratings were low. In full sun, plants were smaller overall. In a second experiment, A. obesum ‘Red’ produced the highest shoot dry weight when grown 20 weeks at 30% or 50% shade with 1.4 g of N per pot. Root formation is an important measure of aesthetic value for this crop. As plants mature, roots enlarge dramatically and are often washed to expose sculptural forms. The highest root dry weights were measured at 1.4 g of N under both full sun and 30% shade.

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A simple and effective method for quantification of leaf variegation was developed. Using a digital camera or a scanner, the image of a variegated leaf was imported into a computer and saved to a file. Total pixels of the entire leaf area and total pixels of each color within the leaf were determined using an Adobe Photoshop graphics editor. Thus, the percentage of each color's total pixel count in relation to the total pixel count of the entire leaf was obtained. Total leaf area was measured through a leaf area meter; the exact area of this color was calculated in reference to the pixel percentage obtained from Photoshop. Using this method, variegated leaves of ‘Mary Ann’ aglaonema (Aglaonema x), ‘Ornate’ calathea (Calathea ornate), ‘Yellow Petra’ codiaeum (Codiaeum variegatum), ‘Florida Beauty’ dracaena (Dracaena surculosa), ‘Camille’ dieffenbachia (Dieffenbachia maculata), and ‘Triostar’ stromanthe (Stromanthe sanguinea) were quantified. After a brief training period, this method was used by five randomly selected individuals to quantify the variegation of the same set of leaves. The results were highly reproducible no matter who performed the quantification. This method, which the authors have chosen to call the quantification of leaf variegation (QLV) method, can be used for monitoring changes in colors and variegation patterns incited by abiotic and biotic stresses as well as quantifying differences in variegation patterns of plants developed in breeding programs.

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Hops (Humulus lupulus) is a perennial, herbaceous crop cultivated for its strobiles, or cones, which contain a resinous compound used for flavoring and aroma in food, tea, and beer. The United States is the second largest global producer of hops with greater than 15,000 ha in production. Increased demand for hop products has recently resulted in production of hops in nontraditional production areas (non-Pacific northwest U.S. region). To examine cultivation potential of hops within the southeastern United States, 60 hop rhizomes consisting of four varieties were transplanted into native, deep sand soil (Candler and Tavares-Millhopper soil series) within a protected, open-sided greenhouse and evaluated for growth, strobile yield, and brewing values for a period of 2 years. Plant bine length was recorded weekly for 20 weeks throughout year 1 with mean bine lengths of 609, 498, 229, and 221 cm at harvest for ‘Chinook’, ‘Columbus’, ‘Amalia’ and ‘Neo1’, respectively. Mean harvested strobile dry weight recorded for year 1 was 21.2, 17.9, 9.0, and 8.2 g/plant for ‘Columbus’, ‘Chinook’, ‘Neo1’ and ‘Amalia’, respectively. With the exception of ‘Neo1’, mean strobile mass was lower for all cultivars during year 2 with 16.6, 10.3, 25.8, and 2.6 g/plant for ‘Columbus’, ‘Chinook’, ‘Neo1’ and ‘Amalia’, respectively. Alpha acid concentrations by percentage strobile mass for year 1 were 6.8%, 9.7%, 3.8%, and 4.3% for ‘Columbus’, ‘Chinook’, ‘Amalia’, and ‘Neo1’, respectively. Alpha acids varied year 2 with concentrations of 4.8%, 10.4%, and 5.6% for ‘Columbus’, ‘Chinook’, and ‘Neo1’, respectively. Findings support viability of hop production in the southeastern United States and establish the benchmark for future varietal trialing investigations.

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Leaf explants derived from in vitro–grown shoots of blueberry cultivars Bluejay, Pink Lemonade, Sunshine Blue, and Top Hat were cultured on woody plant medium (WPM) supplemented with 9.12 μm 6-(4-hydroxy-3-methylbut-2-enylamino) purine or zeatin (ZT) in combination with 1.23, 2.46, or 4.92 μm indole-3-butyric acid (IBA). Calluses were induced from the explants and adventitious shoots were regenerated. ‘Sunshine Blue’ and ‘Top Hat’ produced more than four shoots per explant but shoot numbers were less than one for each ‘Pink Lemonade’ explant and about 0.2 per ‘Bluejay’ explant. The results indicate that there is significant difference among cultivars in indirect shoot organogenesis. The differences may be related to their diverse genetic background as they are polyploid hybrids. Microcuttings derived from adventitious shoots of ‘Sunshine Blue’ rooted in vitro in WPM medium supplemented with 9.84 μm IBA and also rooted ex vitro in a peat-based substrate after cuttings were dipped or not dipped in IBA solutions. Direct rooting of microcuttings in the peat-based substrate was effective, suggesting that in vitro rooting may not be necessarily needed. Survival rate of ex vitro–rooted plants in a shaded greenhouse was high, more than 90%. The established shoot regeneration protocols could be used for rapid propagation of ‘Sunshine Blue’ and ‘Top Hat’ and for cultivar improvement through genetic transformation.

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Colchicine application successfully induced tetraploids from in vitro-cultured diploid Dieffenbachia × ‘Star Bright M-1’. Shoot clumps, each with six to eight small, undifferentiated shoot primordia, were cultured in liquid Murashige and Skoog (MS) medium and treated with colchicine at rates of 0, 250, 500, or 1000 mg·L−1 for 24 h. In vitro survival of shoot clumps significantly decreased as colchicine concentrations increased. Shoot clumps that survived were transferred to colchicine-free MS medium containing 2.0 mg·L−1 N6-isopentenyl) adenine and 0.10 mg·L−1 indole-3-acetic acid. Shoots were harvested during four subsequent subcultures and planted in a soilless substrate in a shaded greenhouse. The number of plants that survived 6 months after ex vitro planting was 690, 204, 59, and 69 for colchicine treatments at 0, 250, 500, and 1000 mg·L−1, respectively. The 332 plants from colchicine treatments along with 90 control plants (selected from 690 in the control treatment) were evaluated morphologically in a shaded greenhouse. Overall plant growth, including crown height, plant canopy, and leaf size, of colchicine-treated plants was significantly less than controls. Based on the growth data, 10, 32, 15, and 16 plants from the 0, 250, 500, and 1000 mg·L−1 colchicine rates, respectively, were selected and analyzed by flow cytometry. Flow cytometry confirmed the presence of 13 tetraploids and 29 mixoploids among the 63 colchicine-treated selections; all 10 plants from the control were diploid. A colchicine rate of 500 mg·L−1 produced a higher percentage of tetraploids (10.2%) than did the 250 (2.9%) or 1000 mg·L−1 (1.4%) rates. Subsequent comparisons showed tetraploids had significantly smaller and thicker leaves, greater specific leaf weights, and longer stomata than diploids. Tetraploids also showed increased net photosynthetic rate, decreased g S, decreased intercellular CO2 concentration, decreased transpiration rate, and increased water use efficiency. Tetraploids appeared robust and their smaller size could make them potentially more durable plants used as living specimens for interior decoration.

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‘Jincuilei’ is a mutant selected from Lonicera macranthoides Hand.-Mazz. It produces abundant flowers that never open with a chlorogenic acid (CGA) content up to 6.0%. Propagation through rooting or grafting has only a 30% survival rate. This study was undertaken to establish an efficient protocol for rapidly regenerating this mutant. Leaf explants were inoculated on Gamborg's B5 medium supplemented with different concentrations of 6-benzyladenine (BA) and 2,4-dichlorophenozyacetic acid (2,4-D). The optimal combination for callus induction was 4.4 μm BA with 2.26 μm 2,4-D, which resulted in 86.7% of leaf explants producing calluses in 4 weeks. Calluses produced from this optimal medium were cultured on B5 medium containing different concentrations of kinetin (KT) and α-naphthalene acetic acid (NAA). The best formulation for shoot induction was B5 medium containing 0.9 μm KT and 5.4 μm NAA in which 73.4% of cultured calluses produced shoots in 8 weeks, and shoot numbers ranged from three to six per callus piece (1 cm3). Adventitious shoots were cut and rooted in half-strength Murashige and Skoog medium supplemented with 14.8 μm 3-indolebutyric acid. Roots initiated 10 d after culture, and rooting percentages ranged from 98% to 100%. Plantlets grown in a container substrate in a shaded greenhouse had over a 95% survival rate. During the last 6 years, over four million plantlets were regenerated using this established procedure, and there was no somaclonal variation. Fresh and dry weights of 1000 flowers, CGA contents, and dry flower yields of the regenerated plants were not significantly different from those of the stock ‘Jincuilei’ propagated by cutting, indicating that plants regenerated from this established procedure were stable. This established in vitro culture method has led to rapid commercial production of this medicinal plant on more than 1500 ha of production field.

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This study evaluated chilling sensitivity of eight popular Dieffenbachia cultivars. Tissue culture liners were potted in 15-cm diameter pots using Vergro Container Mix A and grown in a shaded greenhouse under maximum photosynthetically active radiation of 285 μmol·m−2·s−1 for 5 months. After determining growth indices, the plants were chilled in walk-in coolers at 2, 7, or 12 °C for 6, 12, or 24 h. Chilled plants were placed back in the shaded greenhouse for chilling injury and growth evaluation. Visible symptoms of injury included chlorosis, necrosis, water-soaked patches on leaves, or complete wilting. In addition to leaf injury, stems of some cultivars chilled at 2 °C for 24 h became water-soaked at the base, which resulted in the death of either entire shoots or entire plants depending on cultivars. Leaf injury occurred in all cultivars chilled at 2 °C, except for ‘Panther’; and the longer the exposure at this temperature, the greater the injury. No visual injury was observed among plants chilled at 7 and 12 °C except ‘Tropic Honey’ that had 26% of leaves injured at 7 °C. Based on the percentage of injured leaves 12 days after chilling at 2 °C for 24 h, the sensitivity of the eight cultivars ranked as follows: Tropic Honey > Sterling > Carina ≥ Octopus > Camille > Camouflage > Star Bright > Panther. In addition to visual injury, plant growth was also affected by chilling during the subsequent 3 months of growth. All ‘Tropic Honey’ chilled at 2 °C died regardless of the tested chilling duration. Growth indices of all other cultivars except for ‘Panther’ chilled at 2 °C for 24 h significantly decreased compared with those of controls. ‘Camille’, ‘Camouflage’, ‘Carina’, and ‘Sterling’ also exhibited significant growth reduction after chilling at 2 °C for 12 h. This study showed that genetic variation in chilling sensitivity exists among cultivated Dieffenbachia. The identified chilling-tolerant cultivars could be used for breeding of new chilling-tolerant cultivars. The use of chilling-tolerant cultivars in production may reduce the chance of injury during heating outages and shipment.

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This study evaluated the potential for using cowpeat, a composted dairy manure, as a component of container substrates for foliage plant propagation. Using a commercial formulation (20% perlite and 20% vermiculite with 60% Canadian or Florida peat based on volume) as controls, peat was replaced by cowpeat at 10% increments up to 60%, which resulted in a total of 14 substrates. Physical and chemical properties such as air space, bulk density, container capacity, total porosity, pH, carbon-to-nitrogen ratio, and cation exchange capacity of the cowpeat-substituted substrates were largely similar to those of the respective control. However, the electrical conductivity (EC) increased with the increased volume of cowpeat. The 14 substrates were used for rooting single-node cuttings of golden pothos (Epipremnum aureum) and heartleaf philodendron (Philodendron scandens ssp. oxycardium) and three-node cuttings of ‘Florida Spire’ fig (Ficus benjamina) and germinating seeds of sprenger asparagus (Asparagus densiflorus) in a shaded greenhouse. All cuttings rooted in the 14 substrates, and the resultant shoot and root dry weights of golden pothos and ‘Florida Spire’ fig 2 months after rooting did not significantly vary across seven Canadian peat- or Florida peat-based substrates. Shoot dry weights of heartleaf philodendron were also similar across substrates, but the root dry weight produced in the Canadian peat-based control substrate was much greater than that produced in the substrate containing 60% cowpeat. Root dry weight and root length produced in the Florida peat-based control substrate were also significantly greater than those produced in substrates substituted by 60% cowpeat. These results may indicate that cuttings of golden pothos and ‘Florida Spire’ fig are more tolerant of higher EC than those of heartleaf philodendron, as the substrate with 60% cowpeat had EC ≥ 4.16 dS·m−1. Seed germination rates of sprenger asparagus from cowpeat-substituted Canadian peat-based substrates were greater than or comparable to those of the control substrate. Seed germination rates were similar across the seven Florida peat-based substrates. The root-to-shoot ratios of seedlings germinated from both control substrates were significantly greater than those germinated from substrates substituted by cowpeat. This difference could be partially explained by the higher nutrient content in cowpeat-substituted substrates where shoot growth was favored over root growth. Propagation is a critical stage in commercial production of containerized plants. The success in using up to 60% cowpeat in rooting and seed germination substrates may suggest that cowpeat could be an alternative to peat for foliage plant propagation.

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