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Wayne L. Schrader

Growth regulator application effects on earliness and yield were evaluated on drip irrigated artichokes grown as annuals from seed for winter (November through February) production in 1989, 1990, and 1991. Foliar treatments were applied three times at two week intervals. Gibberellic acid treatments which began four, six, and eight weeks after transplanting gave six to eight weeks earlier first harvest and significantly greater yields. Treatment with gibberellic acid beginning four weeks after transplanting gave the earliest first harvest.

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Hiroshi Iwanami, Nobuyuki Hirakawa, Hiroyasu Yamane and Akihiko Sato

Crosses between seedless cultivars had been conducted to produce seedless table grape efficiently by combining with ovule and embryo culture in Vitis vinifera L. But very few plants grew normally in this method. Four plant growth regulators (Cycocel, B-Nine, Uniconazole-P, Ethrel) were applied to shoots 4 weeks before anthesis to develop the seeds of two seedless cultivars `Flame seedless' and `A1706'. Correlation was significant in each cultivar between the shoot length at anthesis and the number of seed traces per berry in all combined treatments. Analysis of covariance revealed that the number of seed traces per berry was significantly higher when the shoots were applied with Uniconazole-P (240 ppm) than B-nine (2000 ppm), Cycocel (500 ppm) and Ethrel (400 ppm) in `Flame seedless' and Uniconazole-P and B-nine than Ethrel in `A1706'. Ovules of these two seedless cultivars crossed with seedless cultivar `Perlette' after the application of four plant growth regulators were cultured on half-strength MS medium with 10 μm IAA and the percentage of developed embryos in ovules was higher when the shoots were applied with Uniconazole-P and B-nine than Cycocel, Ethrel in `Flame seedless' and B-nine than others in `A1706'. These results indicate that the use of certain plant growth regulators promotes the embryo development.

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Jesse R. Quarrels and Steven E. Newman

A leaching frame was constructed to detect residual plant growth regulators in media. The table was 0.9 × 1.8 m and designed to hold 40 10-cm diameter by 30-cm PVC cylinders. Each cylinder was cut lengthwise in half and resealed with duct tape. Rooted cuttings of `Freedom' poinsettias were planted into each cylinder using two media combinations: 2 vermiculite: 2 peat moss: 1 pine bark and 2 vermiculite: 1 peat moss: 2 pine bark (by volume). Four growth regulator treatments were applied to the medium two weeks after transplanting: control, 0.25 mg paclobutrazol, 0.25 mg uniconazole, and 0.125 mg paclobutrazol applied as spike. After plant growth was recorded, the cylinders were removed and sliced lengthwise. Snapdragon plugs were then transplanted into the medium along the length of the cylinder to determine if any residual paclobutrazol remained. Paclobutrazol and uniconazole reduced stem length. The presence of pine bark in the media reduced the effect of the plant growth regulators.

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CC. Lim and S.L. Kitto

Aconitum uncinatum L., a herbaceous native, is not widely available for the public because of difficulties in producing plants via conventional methods. The initial objective was to find a growth regulator combination and an antioxidant concentration that provided increased proliferation rates. Growth regulator combinations examined were BA (0, 11.1, 22.2, 44.4 μm), 2iP (0, 24.6, 49.2 μm), kinetin (0, 23.2, 46.5 μm), IAA (0, 28.5, 57.1 μm), and NAA (0, 26.9, 53.71μm). Antioxidants examined were ascorbic acid (0, 150, 500 ppm), citric acid (0, 150, 500 ppm), PVP (0, 250, 500 ppm), PVPP (0, 250, 500 ppm), and MPP (0, 0.5,1 ppm). Surface response analysis was used to select 30 (of more than 3000 possible) combinations of growth regulator or antioxidant concentrations. Experiments were subcultured every 4 weeks and terminated at 8 weeks. Total-shoot proliferation was significantly greater on media containing 44.4 μm BA + 46.5 pm kinetin. There were six antioxidant combinations that were no different from the control (150 ppm each ascorbic acid and citric acid). Further experiments looking at various BA + kinetin and antioxidant concentrations are needed to refine the media for maximal proliferation.

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Christopher S. Cramer and Mark P. Bridgen

Mussaenda, a tropical ornamental shrub developed in the Philippines is being examined as a potential greenhouse potted crop in the United States. Showy sepals of white, picotee, pink or red and fragrant, yellow flowers make Mussaenda an attractive patted plans however, the profuse upright growth habit of some Mussaenda cultivars is undesirable for pot plant culture. With this in mind experiments were conducted to determine the effects of three growth regulators at two concentrations each, as well as the application method and the number of applications on Mussaenda plant height.

Three growth regulators, daminozide (B-Nine), ancymidol (A-Rest), and paclobutrazol (Bonzi) were applied at two commercially recommended rates and two application methods (spray or drench). The treatment were daminozide at 2500 ppm and 5000 ppm (spray), ancymidol at 33 and 66 ppm (spray) and at 0.25 and 0.50 mg/pot (drench), and paclobutrazol at 25 and 50 ppm (spray) and at 0.125 and 0.25 mg/pot (drench). In subsequent experiments, the same growth regulators were applied with an increase in concentration and either two or three applications. The treatments were daminozide at 5000 ppm (spray), ancymidol at 66 and 132 ppm (spray) and at 0.50 and 1.0 mg/pot (drench), and paclobutrazol at 50 and 100 ppm (spray) and at 0.25 and 0.50 mg/pot (drench).

The most attractive potted plants were produced with two applications of daminozide at 5000 ppm or two applications of ancymidol at 0.5 mg/pot (drench). Higher concentrations or additional applications excessively reduced plant height. Three spray applications of 132 ppm ancymidol also produced an attractive potted plant. Paclobutrazol sprays or drenches at any concentration or application number were ineffective for reducing Mussaenda `Queen Sirikit' plant height.

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Lianghong Chen, Ajmer S. Bhagsari, Soon O. Park and Sarwan Dhir

This study was carried out to optimize conditions for plant regeneration of sweetpotato [Ipomoea batatas (L.) Lam] using shoot tips, petioles, and leaves of Selection 75-96-1 as explants in Murashige and Skoog (MS) with several growth regulators at different levels. Callus initiation and callus proliferation media were 9.0 μm 2,4-dichlorophenoxyacetic acid (2,4-D) and 9.0 μm 2,4-D + 1.1 μm N 6-benzyladenine (6-BA) in protocol I; 8.1 μm α-naphthaleneacetic acid (NAA) + 1.2 μm kinetin (KIN) and 5.4 μm NAA + 4.6 μm KIN in protocol II; 0.9 μm 2,4-D, and 0.9 μm 2,4-D + 1.2 μm N-isopenylamino purine (2iP) in protocol III; NAA (8.1 μm) + KIN (1.2 μm) and 2,4-D (0.9 μm) + 2ip (1.2 μm) in protocol IV, respectively. In protocol I and II, shoot tip, petiole, and leaf were used, but only petiole and leaf in protocol III and IV. In the protocol I and II, somatic embryos were obtained only from shoot tip explants; in protocol III and IV, only from petioles. The frequencies of somatic embryo development were 33.3% in protocol I, 42.1% in protocol II, 21.2% in protocol III, and 10.3% in protocol IV, respectively. The leaf explants failed to produce somatic embryos in all the experiments. In protocol I, somatic embryogenesis occurred through the well-known sequence of globular-, heart-shaped-, torpedo-, and cotyledon-type embryos. However, in protocol II, the structures resembling plumule and radicle were observed before the emergence of torpedo/cotyledon type embryo clusters. The somatic embryogenesis in protocol III and IV was similar to that in protocol I. Growth regulators influenced somatic embryo development. Further, this study showed that explant resource and growth regulators affected the frequency of plant regeneration in sweetpotato.

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Todd J. Cavins

Anti-gibberellin plant growth regulators (PGRs) not only affect cell elongation, but other biochemical processes. The experimental PGR A-1699 DF was evaluated for efficacy of height and width control as well as effect on flower petal pigmentation. While the active ingredient in A-1699 DF has proven effective for height control on several crops, that was not observed on Impatiens `Accent Cranberry' in this study. However, A-1699 DF did affect flower petal pigmentation. A-1699 DF likely inhibited anthocyanin production that resulted in light pink versus cranberry flower petals observed on the control, Paczol, and B-Nine/Cycocel PGR applications.

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Jin Wang and Virginia R. Walter*

The effect of vernalization and two growth regulators Fascination™ and Pro-Gibb® on the growth, inflorescence development and flowering of Ornithogalum `Chesapeake Snowflake' was studied. Regardless of bulb size, chilling bulbs for 3 weeks at 10°C before planting accelerated flowering of the first inflorescence and shorten leaf length by 3-5cm as compared to non-chilled bulbs. Fascination™ 10% 100 μL and Pro-Gibb® 200 ppm accelerated flowering of first inflorescence by large bulbs (8- to 10-cm circumference) as compared to controls. PGR treatments appear to have no effect on small bulbs (3-5-cm circumference).

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Rosanne E. Franco and Susan S. Han

Senescence of excised Easter lily leaves is typically marked by a rise in respiration without a concomitant production of ethylene. Treating excised leaves with 500 mg·L-1 of gibberellic acid (GA3) or benzyladenine (BA) significantly delayed the onset of leaf yellowing, lowered the respiration rates by one-third to one-half, and markedly delayed the respiratory rise. Similar effects on respiration were detected in leaves treated with BA or GA3 before a 4-week period of cold storage and in leaves treated after chlorosis had initiated. Results of this study indicate that excised Easter lily leaves respond to the growth regulators with a significant decrease in respiration rate.

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Allen D. Owings and Steven E. Newman

The action of foliar-applied uniconazole, paclobutrazol, dikegulac-sodium, ancymidol, 6-BA, GA4+7, and 6-BA + GA4+7 On container–grown Photinia × fraseri was studied over a one year period. Vegetative growth habit was evaluated at three month intervals. Shoot dry weight and histological examination of stern anatomy in the apical meristematic region was conducted at experiment termination.

Several plant growth regulators, primarily uniconazole, 6-BA, 6-BA + GA4+7, and dikegulac-sodium, stimulated lateral branching. Linear increases in lateral branching occurred as application rates increased. High application rates of uniconazole and paclobutrazol created an asymmetrical growth habit and decreased dry weight accumulation.