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Allen D. Owings and Steven E. Newman

Four rates of seven plant growth regulators were foliar-applied to 11.4 liter containers of Photinia × fraseri after initial root establishment. Growth regulators studied were uniconazole, paclobutrazol, dikegulac-sodium, ancymidol, 6-BA, GA4+7 and, 6-BA + GA4+7. Six months after application, plant height, plant width, growth index, and number of lateral and terminal branches were recorded.

Applications of uniconazole (30 mg a.i./liter), 6-BA alone or in combination with GA4+7, and dikegulacsodium stimulated lateral branching. The number of lateral branches increased linearly as paclobutrazol rates increased from 60 to 180 mg a.i./liter. Growth index decreased with increasing application rates of uniconazole and paclobutrazol, while the growth index of photinia treated with other growth regulators wasn't affected by application rate. Plant height was increased in GA4+7 treated plants.

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Pascal Nzokou and Paligwende Nikiema

creates a challenge for researchers to develop treatments or approaches that will improve tree resistance to frost damage in case of warm winter temperatures. One potential solution is the use of plant growth regulators (PGRs) to influence the natural

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Susan S. Han

The development of greenhouse leaf yellowing in Easter lilies (Lilium longiflorum Thunb.) was significantly reduced by the application of growth regulator solutions containing gibberellins 4 and 7 (GA4+7) or benzyladenine (BA). Solutions containing BA alone significantly reduced leaf yellowing on plants caused by close spacing but were less effective than GA4+7. Application of BA alone, however, was not effective against root rot-induced leaf yellowing. When plants were treated with GA4+7 or BA + GA4+7 around the visible bud stage, nearly all of the leaves remained green until the end of the growing season. These growth regulators, however, increased the final height of the plants by 8–10 cm. The developmental rate and size of the flower buds, as well as the length of the pedicels were not affected by the growth regulator treatments. Thus application of these growth regulators greatly improved the quality of the leaves without compromising the quality and timing of the flowers. Chemical name used: N-(phenylmethyl)-1H-purine-6-amine (benzyladenine, BA).

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Stanislav Magnitskiy*, Claudio Pasian and Mark Bennett

Regulation of excessive vegetative growth is of importance in both field and bedding plant production. The goal of the study was to evaluate the effect of preplant seed soaking in growth regulators on the growth control of floricultural (verbena, salvia, pansy, marigold, celosia) and agronomic (cucumber, dill) crops. Seeds were soaked in water solutions of growth regulators of different concentrations ranging according to the crop from 50 to 1000 mg·L-1 for paclobutrazol, 1 to 10 mg·L-1 for uniconazole, 10 to 200 mg·L-1 for ancymidol, 100 to 5000 mg·L-1 for chlormequate chloride and dried at 20 °C for 24 h prior to sowing into plugs. In the first experiment, seeds of verbena, salvia, pansy, and dill soaked for 5 minutes in 50 mg·L-1 paclobutrazol solutions produced seedlings that were up to 43, 18, 30, and 22% shorter than the controls, respectively. Increased paclobutrazol concentrations and soaking time generally corresponded to a greater reduction of plant height, as well as delays and reduction in seedling emergence of all crops, except cucumber. In the second experiment, growth of marigold plugs from seeds soaked in 5 mg·L-1 uniconazole or 60 mg·L-1 ancymidol solutions during 45 min was associated with 23% or 6% plant height reduction, respectively. Soaking of marigold seeds in the solutions of chlormequate chloride did not significantly affect seedling growth. Increasing time of seed soaking in growth regulator solutions did not influence emergence of marigold seedlings. The height of celosia seedlings was only slightly reduced by soaking seeds in the solutions of all studied growth regulators. Results indicate that seed treatments with growth regulators might be useful in growth control of selected bedding plants.

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Theophilus Asante* and Guochen Yang

The role of plant growth regulators in enhancing axillary shoot proliferation, callus production and root initiation of the American chestnut (Castanea dentata) was investigated. Micropropagated shoots were used as explant materials. Different concentrations of indoleburytic acid (IBA), kinetin, N-(2-chloro-4-pyridyl)-N'-pheylurea (CPPU), naphtha-leneacetic acid (NAA), thidiazuron (TDZ), zeatin, 2,4-dichlorophenoxyacetic acid (2,4-D), and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) were added to McCown woody plant medium (WPM) to evaluate their effects on in vitro shoot proliferation, callus production, and root initiation. Differences in the number of shoots (primordia), morphology of micropropagated shoots, and amount of callus were observed between the plant growth regulator treatments and concentrations. Explants cultured in media containing CPPU or TDZ produced more shoots (primordia). Callus production increased from NAA to IBA to 2,4-D to 2,4,5-T.

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Hyo-Geur. Park, Kyung-Young Choi and Do-Hyun Lee

Hot pepper is the most important vegetable in Korea in terms of both acreage and product value. Morphogenic response in tissue culture of hot pepper varied greatly with explant source and growth regulators. Somatic enbryogenesis, which we believe had not been reported yet, was only induced from 5-month-old callus derived from anther culture. Embryogenic callus was solely observed in the MS medium supplemented with 2 mg/l of NAA and 2 mg/l of BA. Better somatic embryogenesis and plant regeneration was observed on hormone free medium. Adventitious organogenesis was well induced from both hypocotyl and cotyledon. Polarity of explant for shoot regeneration was observed. Success rate of regeneration has been continuously improved mainly due to combinations of growth regulators. The best combination so far was 2 mg/l of zeatin and 1 mg/l of IAA, resulting in 92% of regeneration from cotyledon explant.

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Lurline Marsh, Rufus Jones and Mark Ellersieck

Growth and fruiting pattern of okra (Abelmoschus esculentus L. Moench) cv. Clemson Spineless as affected by the growth regulators Alar (N -dimethylaminosuccinamic acid) and ethephon (2-chloroethyl phosphoric acid) were evaluated in field studies. Eight treatments consisting of Alar at 600, 1200, 2400, and 3600 μl·liter-1 and ethephon at 200, 400, 600, and 800 μl·liter-1 and water control were applied as foliar sprays at the three- to four-true-leaf stage. Both growth regulators depressed shoot growth and leaf production. Ethephon reduced shoot length. Total fruit yield was not significantly affected by the treatments. However, ethephon-treated plants tended to produce fewer fruits and lagged behind Alar-treated plants and the control plants in Fruit production during the early harvests.

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Ursula K. Schuch, Leslie H. Fuchigami and Mike A. Nagao

Unsynchronized flowering and fruit ripening of coffee prohibits mechanical harvesting and results in high labor costs. Coffee (C.arabica c. Guatemalan) trees were sprayed at the beginning of the 1988 and 1989 flowering season with solutions of benzyladenine (BA), gibberellic acid GA3 (GA), and Promalin (PR) or were pruned in 1988 to determine effects on synchronizing flowering and ripening. Growth regulators affected the time to flowering and harvesting compared to the control, however, treatment effects were dependent on the time of growth regulator application. Application of PR and GA at 100 mg/l in Jan 1988 shortened the average days to flowering by 16 and 13 days, and the average days to harvest by 15 days compared to the control. Pruning of three apical nodes of primary lateral branches in Feb 1988 caused delays in flowering, reduced flower and fruit number per tree, and caused branch dieback.

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Susan S. Han

Yellowing of excised Easter lily leaves was significantly delayed by foliar application of gibberellic acids (GA3) ≥ 250 mg·1-1 or benzyladenine (BA) ≥ 50 mg·1-1. Rapid development of foliar chlorosis following cold storage was delayed significantly by applying 500 mg·1-1 of GA3 or BA before storage. Post-storage treatments were less effective. Development of chlorosis was associated with rapid loss of fresh weight and was not related to the aperture of the stomates. Respiration rate of leaves treated with growth regulators were significantly lower than that of the controls. Differences in the rate of carbohydrate depletion may explain the striking effects of growth regulators on the development of foliar chlorosis.

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Eddie B. Williams, William F. Hayslett and Sabrina L. Shaw

Growth regulators were applied on Iridon Chrysanthemums during the month of January, 1993 to determine their response. The growth regulators used were uniconizole, [(E)-(+)-(S)-I-(4-chlorophenyl)-4,4 dimethyl-2-(1,2,4-trazol-lyl)-1-pent-lene-3-01],daminozide [(butanedoic acid mono (2,2dimethyl hydraide)], ancymidol [a-cyclopropyl-a-(p-methoxy-phenyl)-5-pyridinemethanol] and chlormequat* (2-chloroethyl) trimethylammonium chloride (not labeled for mums). The daminozide treated plants received a second application 14 days after the initial treatment. Peters 20-20-20 NPK water soluble all purpose fertilizer were used for all treatments.

There were significant differences in plant height, total fresh weight, total dry weight, total number of flowers, and total number of buds due to treatment. Uniconizode had the greatest effect on plant height, and the other parameters observed. Although there were differences between the uniconizide and daminozide treated plants for number of flowers and number of buds, these differences were not significant.