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D.J. Tennessen

Increased plant density can reduce the per-plant cost of ornamental and vegetable crop production, but also reduces the quality of the crop produced. Plants grown under these conditions exhibit internode elongation and yellow leaves. This response generally is described as a shade-avoidance response. Genetically transformed tobacco that express oat Phytochrome-A (Phy-A) grew short in white light but grew as tall as the nontransformed control (10 cm) in red light. When a mixture of red and 5% far-red (700 to 750 nm) was used, transformed tobacco remained short (5 cm) and dark green, whereas nontransformed grew taller (27 cm). The concept of masking the shade avoidance response was tested in transformed lines of tomato (Boylan and Quail 1989) that express elevated oat Phy-A. Transformed plants remained short and dark-green in shade-light. Phy-A may be a useful strategy to mask the shade-avoidance response.

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Shuguang Wang, Yongpeng Ma, Chengbin Wan, Chungyun Hse, Todd F. Shupe, Yujun Wang, and Changming Wang

this paper, the spatial distribution patterns of endogenous IAA and ABA, and their dynamic changes during shoot elongation of Fargesia yunnanensis were investigated. The correlation between phytohormones and bamboo internode elongation was also

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Robert D. Berghage and Royal D. Heins

Elongation characteristics of each internode on a lateral shoot of poinsettia (Euphorbia pulcherrima Klotz) `Annette Hegg Dark Red' were determined from pinching through anthesis for plants grown with 36 day/night temperature (DT/NT) combinations between 16 and 30C. The Richards function was used to describe the elongation of each internode. The first internode developing on a lateral shoot was longer and matured faster than subsequent internodes. The length of the first internode was a function of the difference between day and night temperatures (DIF = DT - NT). Subsequent internodes elongated uniformly in the absence of flower initiation. In the absence of flower initiation, the length of an internode, after the first, was a function of DIF. Internodes were shorter as proximity to the inflorescence increased. Internode length after the start of short days was a function of DIF and the visible bud index where visible bud index = [(days from pinching to the day an internode began to elongate - days from pinching to the day of the start of flower initiation)/the number of days from pinching to visible bud]. A poinsettia lateral shoot elongation model was developed based on the derived functions for internode elongation. The model predicted lateral shoot length within one standard deviation of the mean for plants grown in a separate validation study with 16 combinations of DT/NT. The model allows the prediction of lateral shoot length on any day from pinching through anthesis based on temperature, the number of nodes on the lateral shoot, the time each internode on the lateral shoot began elongating, and the visible bud index at the start of elongation of each node.

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Terri W. Starman, Melissa C. Robinson, and Kristen L. Eixmann

Plant response to ethephon treatment was tested on 27 cultivars of vegetative annuals that have spreading and trailing growth habits. A control treatment was compared to 500 and 1000 mg·L-1 (ppm) foliar spray treatments of ethephon. Plant height and/or width index were significantly reduced for 81% of the cultivars tested. Responsive cultivars were alternanthera (Alternanthera dentata), brachyscome (Brachyscome iberidifolia) `Toucan Tango'; calibrachoa (Calibrachoa hybrids) `Colorburst Red', `Million Bells Cherry Pink', and `Trailing Pink'; diascia (Diascia × hybrida) `Sunchimes Rose' and `Red Ace'; double impatiens (Impatiens wallerana) `Tioga Red' and `Tioga White'; sweetpotato vine (Ipomoea batatas) `Sweet Caroline Bronze'; lantana (Lantana camara) `Patriot Cherry' and `Samantha'; nemesia (Nemesia × hybrida) `Aromatica Dark Lavender', `Blue Bird', and `Blueberry Sachet'; nolana (Nolana paradoxa) `Blue Eyes'; ivy geranium (Pelargonium hybrida) `King of Balcon'; petunia (Petunia × hybrida) `Cascadia Pink', `Mini Bright Pink', and `Supertunia Mini Purple'; bacopa (Sutera cordata) `Bridal Showers'; and vinca vine (Vinca minor) `Illumination'. Ethephon was not effective on monopsis (Monopsis unidentata) `Royal Flush', persicaria (Persicaria microcephala) `Red Dragon', or calibrachoa `Liricashower Rose'. Different cultivars of petunia showed varied responses to ethephon treatments as did trailing snapdragon (Antirrhinum majus) `Chandelier Yellow' and `Luminaire Yellow'. Flower number was reduced in 55% of the cultivars due to a delay in flowering. The experiment finds efficacy of ethephon for most cultivars treated at rates greater than or equal to that used commercially, however more research is needed to determine optimum concentrations for the specific cultivars. Chemical name used: ethephon [(2-chloroethyl) phosphonic acid].

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Ariana P. Torres and Roberto G. Lopez

characteristics of floriculture seedlings and plugs are increased biomass (shoot and root), compactness (reduced internode elongation and proportional height), and adequate leaf area to promote growth and development after propagation ( Faust et al., 2005 ; Lopez

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Janelle E. Glady, N. Suzanne Lang, and Erik S. Runkle

, inhibit internode elongation, and stimulate branching. By controlling these plant responses, ethephon has become popular for its ability to streamline crop production schedules in several annual bedding plant crops, including ivy geranium [ Pelargonium

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Qiansheng Li, Min Deng, Jianjun Chen, and Richard J. Henny

also becoming popular in the United States as a potted house plant or bonsai. However, there are two common problems associated with its growth and use under low light conditions, leaf abscission and accelerated internode elongation, which are similar

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Kellie J. Walters and Roberto G. Lopez

., 1976 ). It is labeled for foliar spray applications on floriculture crops to increase lateral branching, abort flowers and flower buds, and inhibit internode elongation ( Currey et al., 2016b ; Hayashi et al., 2001 ); although not labeled, recent

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Joan John, William Courtney, and Dennis R. Decoteau

The effects of light spectral quality on Discorea alata cv, Oriental in vitro grown plantlets were investigated. Cultured nodes were treated with red (R) or far-red (FR) light at the end of a 14 hr photoperiod. End-of-day (EOD) light treatments did not affect organogenesis. EOD FR light increased average internode lengths as compared to plantlets treated with EOD R light. The EOD FR enhancement of internode elongation was reversed by following the FR with R suggesting the involvement of phytochrome. There were no residual light effects on subsequent plantlet development from subcultured nodes or potted plantlets after EOD light treatments were terminated.

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Nihal C. Rajapakse, Margaret J. McMahon, and John W. Kelly

The response of `Bright Golden Anne' and `Spears' chrysanthemum plants to EOD-R or FR light was evaluated to determine the involvement of phytochrome in regulation of plant morphology under CuSO4 filters. Light transmitted through the CuSO4 filter significantly reduced height, internode length and stem dry weight of `BGA' and `Spears' chrysanthemum plants. However, the degree of response varied with the cultivar. Exposure to EOD-FR reversed the reduction of plant height, internode length and the stem dry weight caused by the light transmitted through CuSO4 filters to a level comparable with control plants. Exposure to EOD-FR did not significantly alter height and stem dry weight under control filter Exposure to EOD-R light reduced the height and stem dry weight of `BGA' plants grown under control filter but EOD-R had no effect under CuSO4 filters. In `Spears' plants, EOD-R caused stem dry weight reduction under control filters, but did not reduce stem or internode elongation. The results suggest phytochrome may be involved in controlling plant response under CuSO4 filters. However, there are evidence to indicate that an additional mechanism may be acting on stem/internode elongation.