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A. N. Lakso and S. G. Carpenter

Abstract

Treatment of headed-back 1-year-old dormant shoots of ‘Monroe’, ‘McIntosh’ and ‘Wayne’ apple (Malus domestica Borkh.) with 1% naphthaleneacetic acid (NAA) in latex paint was relatively ineffective and gave inconsistent results; however, treatment of mechanically hedged shoots on established trees gave statistically significant reductions in regrowth, by reducing bud break of dormant buds on older wood. Regrowth in ‘Monroe’ trees was reduced with daminozide primarily by reducing shoot length.

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H.C. Wien and Yiping Zhang

A series of greenhouse experiments was conducted with `Shamrock' bell pepper (Capsicum annuum L.) to gain insight into the flower abscission mechanism and to investigate methods to reduce reproductive structure abscission due to low light intensity. Foliar sprays of STS reduced stress-induced abscission. Application of the synthetic auxin NAA to the ovary substituted for pollination to effect fruit set under nonstress conditions, but did not improve fruit set compared to pollinated controls under low-light stress. Ovary treatment with GA3 and BA either alone or combined with NAA had similar results to NAA treatment alone. Foliar sprays of NAA or CPA also did not improve fruit set under low-light stress conditions. Application of NAA in an aqueous paste to the abscission zone prevented abscission but inhibited fruit growth. Taken together, the results indicate that stress-induced abscission is not prevented by auxin application to the ovary or foliage. The interaction of ethylene and auxin in reproductive structure abscission under stress conditions requires further investigation. Chemical names used: 6-benzylaminopurine (BA), p-chlorophenoxy acetic acid (CPA), gibberellic acid (GA,), silver thiosulfate (STS).

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Kenneth W. Mudge

Abstract

Excised embryos and explants from 2-week-old and 4-month-old seedlings of Mugo pine (Pinus mugo Turra var. mugo) were cultured in vitro on nutrient media containing BA and NAA. Shoot development on intact embryos occurred primarily via adventitious bud formation that was greatest On a medium containing 44.4 μM BA and 0.05 μM NAA. Subsequent shoot elongation was improved by transferring buds to a growth regulator-free medium containing 1 g/liter activated charcoal (AC). After removal from culture, shoots rooted in response to treatment with 0.8% IBA. Chemical names used: N-(phenylmethyl)-1H-purin-6-amine (BA); 1-naphthaleneacetic acid (NAA); and 1H-indole-3-butanoic acid (IBA).

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Abraham H. Halevy and Anton M. Kofranek

Abstract

Pot roses (Rosa hyb. cvs. Pink and Orange Margo Koster and Red Garnette) were sprayed with naphthaleneacetic acid (NAA) or 6-(benzylamino)-9-(2-tetrahydropyranyl)-9H-purine (PBA) prior to simulated truck shipment which lasted 5 or 6 days to study the effect on flower bud and leaf abscision and on leaf senescence. “Shipment” under refrigerated conditions (1-3°C) prevented bud and leaf abscission. ‘Red Garnette’ and ‘Orange Margo Koster’ had little or no bud and leaf abscission even at a warm “shipping” temperature (20-22°C); however, ‘Pink Margo Koster’ was severely affected. Observations under “home conditions” for 10 days after this warm “shipping temperature” revealed that all 3 cultivars had severe leaf senescence. NAA spray (15 and 30 ppm) severely accelerated leaf abscission and senescence. NAA prevented bud drop, but the buds did not open. PBA (50 ppm) greatly reduced leaf abscission both during “shipment” and in “home conditions”. PBA also prevented bud drop and flowers subsequently opened normally.

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M. H. Deaton, J. W. Buxton, and T. R. Hamilton-Kemp

Abstract

Excised flower buds of Nicotiana affinis were grown to maturity in media in which growth regulators were added to evaluate their effects on growth and development. As the concentration of naphthaleneacetic acid (NAA) was increased from 10-7 to 10-4 m, the number of days required for the buds to open decreased, and the number of days required for the corolla tubes to turn brown increased. Indoleacetic acid (IAA) and indolebutyric acid (IBA) did not affect the rate of bud opening. As the concentration of IBA was increased, however, the days required for the corolla tubes to turn brown increased, but not as much as for buds in media with NAA. IAA had no effect on browning of corolla tubes. At high concentrations of NAA and kinetin the corolla tubes were shortened. Kinetin did not affect the rate of bud opening or days till the corolla tubes turned brown.

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Sheldon C. Furutani, Gaylen Shigenaga, and Mike A. Nagao

Abstract

Spray applications of NAA or NAA ethylester at 1000 ppm acid equivalent (A.E.) reduced axillary bud number by 30% and 21%, and weight by 73% and 52%, respectively, on pinched potted chrysanthemums, Chrysanthemum ×morifolium Ramat. ‘Mountain Snow’ and ‘Mountain Peak’. Diameter of floral sprays and vegetative heights also were reduced with increasing concentrations. Flower number was not affected by the treatments. NAA treatments caused leaf epinasty, but NAA ethylester treatments did not. Chemical names used: 1-naphthaleneacetic acid (NAA).

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Robert E. Rouse

Tre-Hold, a commercially available sprout inhibitor containing ethylnaphthaleneacetate (NAA) for newly planted citrus trees in orchards was effective to prevent axillary bud growth on rootstock seedlings in the nursery. Tre-Hold applied at formulated concentration (1×), three-fourths (3/4×), and one-half (1/2×) to field-grown and container-grown greenhouse seedlings prevented sprouting. It was possible to control dormancy of individual buds without affecting adjacent buds. When applied to green citrus tissue, no phytotoxicity occurred. Full concentration of Tre-Hold was found to prevent scion bud healing of container-grown trees when the seedling was treated before budding. Application a few days before unwrapping and after the scion bud had healed did not affect bud healing or budling growth.

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Richard P. Marini, Ross E. Byers, Donald L. Sowers, and Rodney W. Young

Five apple (Malus domestica Borkh.) cultivars were treated with dicamba at concentrations of 0 to 200 mg·liter-1 during 3 years. Although the response varied with cultivar, dose, and year, dicamba always delayed fruit abscission. At similar concentrations, dicamba usually reduced fruit drop more than NAA, but less than fenoprop. Dicamba at 10 mg·liter-1 effectively delayed drop of `Delicious', whereas 20 to 30 mg·liter-1 was required for `Red Yorking', `Rome', `Winesap', and `Stayman'. Dicamba did not influence flesh firmness, soluble solids content, water core, or starch content at harvest or after storage. Chemical names used: naphthaleneacetic acid (NAA); 2-(2,4,5-trichlorophenoxy)propionic acid (fenoprop); 3,6dichloro-2-methoxybenzoic acid (dicamba).

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J. Thomas Raese

Abstract

Growth regulators were applied in early autumn to evaluate their effects on induction of cold hardiness in 2-year-old apple shoots, as determined by the conductivity test. Mid-October applications of 500 ppm (2-chloroethyl)phosphonic acid (ethephon), followed 11 days later by 100 ppm of naphthaleneacetic acid (NAA), increased cold hardiness up to 5°C by early November in 1974 and to a lesser extent in 1976. Two annual sprays of succinic acid-2,2-dimethylhydrazide (daminozide, SADH) in June increased cold hardiness slightly (2 to 3°C) in late fall of 1974, 1975, and 1976. However, in 1974 treated trees were no hardier than the controls later in the winter and fruit set on ethephon-treated trees was severely reduced. In most cases, the combined content of fructose, glucose, sucrose, and sorbitol in the 2-year-old wood was slightly higher in treatments that induced cold hardiness in November or December, 1974 than in the controls. Techniques are described for screening growth regulators for induction of cold hardiness and estimating relative cold protection.

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Luping Qu, James Polashock, and Nicholi Vorsa

A very efficient adventitious regeneration (shoot organogenesis) system for cranberry (Vaccinium macrocarpon Ait.) leaves was developed. A basal medium consisting of Anderson's rhododendron salts and Murashige and Skoog's (MS) organics, supplemented with 10.0 μm thidiazuron (TDZ) and 5.0 μm 2ip, was effective for adventitious regeneration from leaves for the five cranberry cultivars tested: `Early Black', `Pilgrim', `Stevens', `Ben Lear', and `No. 35'. Parameters examined included: 1) varying combinations of three plant growth regulators (TDZ, 2ip, and NAA); 2) explant orientation (adaxial vs. abaxial side in contact with the medium); and 3) leaf position relative to the apical meristem from the source plant. Cultivars varied in regeneration frequency, but cultivar × growth regulator interaction was nonsignificant. With optimal treatment conditions, regeneration occurred on more than 95% of the explants, with `Early Black' and `Pilgrim' producing as many as 100 shoot meristems per explant. At all concentrations tested, NAA (as low as 0.1 μm) increased callus formation and significantly reduced regeneration. Emerging adventitious shoots were always observed on the adaxial side of the leaves regardless of explant orientation on the medium. Regeneration was much greater when the abaxial side was in contact with the medium, and was not related to leaf position on the source plants. Elongation of adventitious shoots began ≈2 weeks after transfer to the basal medium without growth regulators. Cuttings of elongated shoots rooted 100% both in vitro in the basal medium and ex vitro in shredded sphagnum moss. The high regeneration efficiency achieved by using this system will be very useful in the application of techniques, such as Agrobacterium- and particle bombardment-mediated transformation. Chemical names used: 1-phenyl-3-(1,2,3-thiadiazol-5-yl) urea (thidiazuron, TDZ); N6-(γ-γ-dimethyallylamino) purine (2ip); α-naphthaleneacetic acid (NAA).