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- Author or Editor: Jianjun Chen x
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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.
‘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.
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.
Four water-based cold protection systems [under-benches mist (UBM), over-roadways mist (ORM), and two among-plants fog (APF1, APF2)] were evaluated for their water use and effectiveness in protecting ornamental foliage plants from chilling injury (CI) under protected shade structures at three commercial locations in Florida. UBM used a two-stage thermostat-controlled system with mist nozzles on 25-cm above-ground risers combined with an overhead retractable heat curtain. Both ORM and APF1 had seasonally applied polyethylene film cladding and manually controlled irrigation systems. The ORM system had the mist nozzles located 1.8 m high and APF1 and APF2 systems had the low-pressure fog nozzles mounted on 25-cm above-ground risers spaced among the plants. Temperature data loggers were placed outside and inside the northwest sections of the shadehouses. ORM and the two APF systems were evaluated during freeze events in 2006, 2007, and 2008 and UBM only in 2007 and 2008. UBM, ORM, and APF1 successfully kept the shadehouse temperatures above critical chilling temperatures for all of the foliage plants. APF2 protected all foliage crops except for jungle drum “palm” (Carludovica sp.) that sustained CI. At the UBM site, the air temperatures recorded inside the shadehouse were ≈17 °C warmer than outside. Both ORM and APF1 maintained adequately warm temperatures inside the shadehouses; however, the fog system maintained equal or higher temperatures than the mist system and used 86% less water. Inside temperatures were lower with APF2 than APF1 although the emitter type was the same and the water application rates were similar. These temperature differences were attributable to the greater APF2 shadehouse surface area (SA) and volume (V) compared with APF1 and indicate that the SA and V of structures being heated need to be considered when designing water-based low-pressure fog heating systems. The ORM and both fog systems conserved water compared with using the conventional sprinkler irrigation systems. These results show the potential of water-based approaches for maintaining shadehouses above chilling temperatures during freeze events.
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.
This study established a method of regenerating Dracaena surculosa Lindl. ‘Florida Beauty’ through indirect shoot organogenesis. Bud, leaf, and stem explants were cultured on a Murashige and Skoog basal medium supplemented with N6-(2-isopentyl) adenine (2iP) at 12.3 and 24.6 μM with 3-indoleacetic acid (IAA) at 0, 1.1, and 2.3 μM, respectively, and 2iP at 36.9, 49.2, 61.5, and 73.8 μM with IAA at 1.1 and 2.3 μM, respectively. Calluses were induced from leaf explants but failed to produce adventitious shoots. Calluses were also induced from stem and bud explants cultured on the basal medium containing 12.3 μM 2iP and 2.3 μM IAA, 24.6 μM 2iP or higher with either 1.1 or 2.3 μM IAA. The highest callus induction frequency was 63.2% from stem explants and 69.6% from bud explants when they were cultured on the basal medium supplemented with 49.2 μM 2iP and 2.3 μM IAA. The highest shoot formation frequency was 65.7% from stem-derived callus cultured on the basal medium containing 61.5 μM 2iP and 1.1 μM IAA and 88% from bud-derived callus cultured with 49.2 μM 2iP and 1.1 μM IAA. The highest number of shoots per piece of stem- and bud-derived calluses was 3.8 and 6.7, respectively. Adventitious shoots developed better root systems in the basal medium supplemented with 2.0 μM IAA. Plantlets after transplantation into a soilless substrate grew vigorously in a shaded greenhouse under a maximum photosynthetic photon flux density of 300 μmol·m−2·s−1. Neither disease incidence nor somaclonal variants were observed in the regenerated population. This established method could be used for efficient micropropagation of D. surculosa, and the availability of tissue-cultured liners could reduce the dependency on imported cuttings, which often bring new or invasive pests into the United States.
Chlorophytum amaniense Engl. ‘Fire Flash’ is a popular exotic ornamental foliage plant as a result of its unique coral-colored midribs and petioles and tolerance to interior low light levels. Currently, demand for propagative materials exceeds the availability of seeds. This study was intended to develop an in vitro culture method for rapid propagation of this cultivar. Leaf and sprouted seed explants were cultured on a Murashige and Skoog basal medium supplemented with different cytokinins with 1.1 μM α-naphthalene acetic acid (NAA) or 2.3 μM 2,4-dichlorophenoxyacetic acid (2,4-D). Leaf explants showed poor responses in callus production and no adventitious shoots were obtained. Callus formation frequencies from sprouted seeds were 71% and 85% when induced by 9.8 μM N6-(2-isopentyl) adenine (2iP) with 1.1 μM NAA and 9.1 μM N-phenyl-N′-1,2,3-thiadiazol-5-ylurea (TDZ) with 1.1 μM NAA, respectively. Adventitious shoots occurred after the induced calluses were subcultured on the same concentrations of TDZ or 2iP with NAA. Shoot formation frequencies from calluses cultured on TDZ with NAA and 2iP with NAA were 92% and 85%, and the corresponding mean shoot numbers were 37 and 31 per piece of callus (1 cm3), respectively. Adventitious shoots rooted at 100% after transferring to the basal medium containing 4.4 μM 6-benzylaminopurine (BA) with 2.7 μM NAA. Plantlets, after transplanting to a soilless substrate were easily acclimatized in a shaded greenhouse under a photosynthetic photon flux (PPF) density of 200 μmol·m−2·s−1. Regenerated plants grew vigorously without undesirable basal branching or distorted leaves. This newly established regeneration method can provide the foliage plant industry with a means for rapidly propagating ‘Fire Flash’ liners in a year-round fashion.