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Douglas A. Cox and Flora F. Whittington

Abstract

Maintaining size and shape of tropical foliage plants used in interior landscapes can be difficult. Both low and high interior light levels can cause undesirable increases in stem length or plant volume, necessitating pruning or replacement with another plant. Although only a few reports (1-5) are available, paclobutrazol has been shown to be effective in reducing the height of many tropical foliage plant species. In addition, paclobutrazol is reported to reduce leaf abcission of plants placed indoors (1, 3, 5) and intensify green leaf color (1, 4). Soil drench applications, because of the persistence of paclobutrazol in soil (6), can maintain plant size for a long time (4).

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James E. Faust and Larry W. Grimes

Stock plants of six herbaceous species (Antirrhinum ×hybrida `Primrose with Vein' L., Chrysocephalum apiculatum `Golden Buttons', Diascia ×hybrida `Sunchimes Coral' Link & Otto, Lavendula dentata `Serenity' L., Osteospermum ×hybrida `Zulu' L., and Verbena ×hybrida `Lanai Bright Pink' L.) received nine different pinch treatments. Stock plants received a first pinch treatment at one of three pinch heights [low (L1), middle (M1), and high (H1)] followed by a second pinch at one of three pinch heights [low (L2), middle (M2), and high (H2)] in a 3 × 3 factorial arrangement. After the two pinches, cuttings were removed weekly from the stock plants. Cutting yield per stock plant increased as pinch height increased from L to H for both the first and second pinch for all species. A low first pinch followed by a low second pinch (L1L2) produced stock plants with the lowest cutting yield, while a high first pinch followed by a high second pinch (H1H2) produced the stock plants with the highest cutting yield for all species, e.g., the percentage increase in cutting yield was 133% for Antirrhinum, 98% for Chrysocephalum, 144% for Diascia, 80% for Lavendula, 250% for Osteospermum, and 44% for Verbena. This study suggests that pinch height during scaffold development of the stock plant is an important tool for increasing cutting production.

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Nihal C. Rajapakse, Roy E. Young, Margaret J. McMahon, and Ryu Oi

The interest in using nonchemical alternatives for growth control of horticultural crops has recently increased due to public concerns for food safety and environmental pollution. Several research teams around the world are investigating alternative growth control measures, such as genetic manipulation, temperature, water and nutrient management, mechanical conditioning, and light quality manipulation. This review discusses the recent developments in light quality manipulation as a nonchemical alternative for greenhouse plant height control.

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Matthew J. Fagerness, John Isgrigg III, Richard J. Cooper, and Fred H. Yelverton

Questions exist as to whether growth-inhibiting chemicals mimic the effects of reduced mowing heights on putting green ball roll. An experiment was initiated during Spring 1997 to investigate ball roll and visual quality parameters of putting greens maintained at 3.2, 4.0, or 4.8 mm with plant growth regulator (PGR) treatments applied monthly over the course of 1 year. Additional experiments were conducted during Fall 1995 and 1996 and Spring 1996 to investigate diurnal PGR effects on ball roll. All experiments were conducted on pure stands of `Penncross' creeping bentgrass (Agrostis palustris Huds). Treatments included trinexapac-ethyl and paclobutrazol, both inhibitors of gibberellin biosynthesis. In the one-year experiment, mowing height was inversely related to ball roll. However, compromises in turfgrass visual quality and shoot density in `Penncross' turf mowed at 3.2 mm make this a questionable mowing height in areas with severe summer conditions. Ball roll during summer months was reduced by PGRs, suggesting that PGRs have little potential as alternatives to decreasing mowing height for increased ball roll. Paclobutrazol reduced turfgrass quality and shoot density during summer months, suggesting that it be used with caution. Other PGRs, particularly trinexapac-ethyl at 0.05 kg·ha–1 a.i., increased afternoon ball roll by as much as 5% to 10% in diurnal experiments. Use of PGRs on creeping bentgrass putting greens may therefore produce short-lived increases in ball roll with subtle to negative effects on bentgrass growth over more extended periods of time. Chemical names used: 4-(cyclopropyl-α-hydroxymethylene)-3,5-dioxocyclohexane carboxylic acid ethylester (trinexapac-ethyl); (+/–)-(R *,R *)-β-[(4-chloro-phenyl)methyl]-α-(1,1dimethylethyl)-1H-1,2,4-triazole-1-ethanol (paclobutrazol).

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Yi-Lun Liao, Wen-Shin Lin, and Shu-Yun Chen

applied as healthy food ( Bhavna et al., 2017 ; Kuo et al., 2012 ; Tseng et al., 2009 ). However, the plant height of ‘Taichung No. 3’ is 2 m taller than expected, which is an obstacle to harvest for farmers. Thus, the development of a shorter variety

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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.

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Anil P. Ranwala, Garry Legnani, Mary Reitmeier, Barbara B. Stewart, and William B. Miller

, and Valent USA for financial aid and materials support, and to the greenhouse staff of the Kenneth Post Laboratory of Cornell University for plant care.

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T.J. Blom, M.J. Tsujita, and G.L. Roberts

Potted bulbs of Lilium longiflorum Thunb. `Ace' and `Nellie White' and Lilium (Asiatic hybrid) `Enchantment' were grown in a greenhouse under ambient photoperiod (APP), 8-h photoperiod by removing twilight from ambient by blackout cloth (8PP), or 8PP extended with 1 hour of low-intensity far-red radiation (9PP). Height of `Ace', `Nellie White', and `Enchantment' increased by 24%, 18%, and 12%, respectively, under APP and by 118%, 100%, and 44%, respectively, under 9PP compared to 8PP. In a second experiment, the effects of reduced irradiance (0%, 25%, 50%, and 75% shade) were determined on the same cultivars grown under APP or 8PP. The effects of APP on height were similar in magnitude for `Ace' and `Nellie White' but were insignificant for `Enchantment' compared to 8PP. Shading increased height linearly for all cultivars. The regression was greater under APP (2.8 mm/percent shade) than under 8PP (1.8 mm/percent shade) for `Ace' and `Nellie White' combined. Plant height of `Enchantment' was less affected by reduced irradiance. For all cultivars, APP or 9PP produced higher stem dry weight compared to 8PP. Shading decreased leaf and bulb dry weight of the Easter lily cultivars.

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Anil P. Ranwala and William B. Miller

. Gloeckner Foundation. Additional support was provided by the Clemson Univ. Ornamental Horticulture Competitive Grants Program. We gratefully acknowledge plant donations from Van Wingerden International, Asheville, N.C., and chemical donations from Abbott

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Soon O. Park, Dermot P. Coyne, James R. Steadman, Paul W. Skroch, and Geunhwa Jung

The objective was to detect molecular markers associated with QTL for partial physiological resistance (PPR) to two white mold (WM) isolates, partial field resistance (PFR), plant architecture (PA), and plant height (PH) in a genetic linkage map constructed using recombinant inbred lines (RILs) from the cross `PC-50' (resistant to WM) × XAN-159 (susceptible to WM). Significant correlations (+0.39 and +0.47) were noted between the WM reactions in the greenhouse and field. A significant but negative correlation (–0.33) was observed between the WM reaction and PH in the field. Six QTL affecting PPR to isolate 152 were found on LGs 4, 5, 7, and 8. Six QTL affecting PPR to isolate 279 were found on LGs 2, 3, 4, 7, and 8. Five QTL for PFR were observed on LGs 2, 5, 7, 8, and 11. Two QTL affecting PA were detected on LGs 7 and 8. Two QTL affecting PH were identified on LGs 7 and 8. On one end of LG 8 marker H19.1250 was significant for PPR to both isolates. On the other end of LG 8 the region closely linked to the C locus was significantly associated with PPR to both isolates, PFR, PA and PH. Marker J09.950 on LG 7 was significantly associated with PPR to both isolates, PFR, PH and seed weight. Marker J01.2000 on LG 2 was the most significant locus for both PPR to the isolate 279 and PFR. QTL on LG 5 were found for PPR to the isolate 152 and PFR. Overall, four of the five QTL affecting PFR were also found for PPR to one or both isolates.