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  • Author or Editor: Richard J. Henny x
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Codiaeum variegatum (L.) Blume, commonly known as crotons, are among the most popular ornamental foliage plants cultivated for either landscaping or interiorscaping. Currently, more than 300 cultivars are available; each has a distinct phenotype, particularly in leaf morphology. Thus far, there is no information regarding their genetic relationships. In this study, genetic relatedness of 44 cultivars of C. variegatum was investigated using amplified fragment length polymorphism (AFLP) markers. Fourteen primer combinations generated a total of 549 AFLP fragments, which were used to estimate genetic distances and construct dendrograms based on the neighbor-joining method. The 44 cultivars were divided into seven clusters, which concurred with the known history of croton geographical isolation, adaptation, introduction, and breeding activities but differed from the classification made by the Croton Society based on leaf morphology. The established genetic relationships could be important for future germplasm identification and conservation and new cultivar development. Additionally, genetic distance among the 44 cultivars was 0.322 or less, indicating that they have a narrow genetic base. The narrow genetic base may indicate that the cultivars were derived from a common progenitor. On the other hand, 81% of the 549 fragments were polymorphic and the average polymorphic information content was 0.22, which suggests that the cultivars are genetically highly polymorphic. The high polymorphisms may be attributed to significant gene loss or gain facilitated by mutation and/or chromosome variation, thus contributing to a wide range of leaf morphological differences among cultivars.

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Syngonium podophyllum ‘White Butterfly’, one of the most popular ornamental foliage plants, is propagated almost exclusively through in vitro shoot culture. Ex vitro rooting, however, has been associated with severe Myrothecium leaf spot (Myrothecium roridum Tode ex Fr.). The objective of this study was to establish a method for regenerating well-rooted plantlets before ex vitro transplanting. Leaf and petiole explants were cultured on a Murashige and Skoog (MS) basal medium supplemented with N-(2-chloro-4-pyridyl)-N′-phenylurea (CPPU), N-phenyl-N′-1,2,3-thiadiazol-5-ylurea (TDZ), 6-benzyladenine (BA), or N-isopentenylaminopurine (2iP) with α-naphthalene acetic acid (NAA) and 2,4-dichlorophenoxyacetic acid (2,4-D), respectively. Calli formed from leaf explants cultured on the basal medium supplemented with CPPU or TDZ with 2,4-D or with NAA as well as from petiole explants cultured on the medium supplemented with BA, CPPU, or TDZ with 2,4-D or NAA. The calli, however, failed to differentiate, and shoot organogenesis did not occur. Culture of nodal explants on the MS basal medium supplemented with 9.84 μm 2iP, 8.88 μm BA, 8.07 μm CPPU, or 9.08 μm TDZ with 2.26 μm 2,4-D resulted in the formation of protocorm-like bodies, adventitious shoots, and subsequently well-rooted plantlets. MS basal medium supplemented with 19.68 μm 2iP and 1.07 μm NAA resulted in the highest percentage (92.9%) of nodal explants producing protocorm-like bodies and an average of 16.9 well-rooted plantlets per nodal explant. Adventitious shoots were able to root in the initial induction medium, but better root development occurred after shoots with protocorm-like bodies were transferred onto MS basal medium supplemented with 9.84 μm 2iP and 2.69 μm NAA. Regenerated plantlets were stable and grew vigorously with 100% survival rates after ex vitro transplanting to a container substrate in a shaded greenhouse.

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Codiaeum variegatum (L.) Blume is one of the most popular ornamental foliage plants. It encompasses more than 300 recognized cultivars valued by their wide range of leaf shapes and vivid foliage colors. Thus far, only limited information is available regarding the genetic basis of their leaf morphological variation. This study investigated the chromosome numbers and karyotypes of seven phenotypically diverse cultivars. Root-tip cells were fixed, mounted, and observed under light microscopy. Results showed that chromosome numbers in the mitotic metaphase of the seven cultivars were high and variable and ranged from 2n = 66, 70, 72, 76, 80, 82, 84, to 2n = 96, indicating that the cultivars are polyploid and some could be aneuploid. Genetic mosaics occurred in one of the seven cultivars. Additionally, each cultivar had its own karyotype. There were no relationships between chromosome numbers or karyotypes and leaf morphology. Results from this study suggest that the morphological diversity among cultivars of this species could be in part attributed to high variation in chromosome numbers and karyotypes.

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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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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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Pachira aquatica Aubl. has recently been introduced as an ornamental foliage plant and is widely used for interiorscaping. Its growth and use under low light conditions, however, have two problems: leaf abscission and accelerated internode elongation. This study was undertaken to determine if production light intensity and foliar application of paclobutrazol [β-(4-chlorophenyl)methyl-α-(1,1-dimethylethyl)-1H- 1,2,4- triazole-1-ethanol] improved plant growth and subsequent interior performance. Two-year-old P. aquatica trunks were planted in 15-cm diameter plastic pots using a peat-based medium and were grown in a shaded greenhouse under three daily maximum photosynthetic photon flux densities (PPFD) of 285, 350, and 550 μmol·m−2·s−1. Plant canopy heights, average widths, and internode lengths were recorded monthly over a 1-year production period. Two months after planting, the plant canopy was sprayed once with paclobutrazol solutions at concentrations of 0, 50, and 150 mg·L−1, ≈15 mL per plant. Before the plants were placed indoors under a PPFD of 18 μmol·m−2·s−1 for 6 months, net photosynthetic rates, quantum yield, and light saturation and compensation points were determined. Results showed that lowering production light levels did not significantly affect canopy height, width, or internode length but affected the photosynthetic light response curve and reduced the light compensation point. Foliar application of paclobutrazol reduced internode length, thereby resulting in plants with reduced canopy height and width and more compact growth form. Paclobutrazol application also reduced the light compensation point of plants grown under 550 μmol·m−2·s−1. Plants with the compact growth form did not grow substantially, dropped fewer leaflets, and thus maintained their aesthetic appearance after placement indoors for 6 months. These results indicated that the ornamental value and interior performance of P. aquatica plants can be significantly improved by producing them under a PPFD range between 285 and 350 μmol·m−2·s−1 and foliar spraying of paclobutrazol once at a concentration between 50 and 150 mg·L−1.

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