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Zhi-Liang Zheng, Zhenbiao Yang, Jyan-Chyan Jang, and James D. Metzger

Height control is a major consideration during commercial production of chrysanthemum [Dendranthema×grandiflora Kitam. (syn. Chrysanthemum×morifolium Ramat.)]. We have addressed this problem by a biotechnological approach. Plants of `Iridon' chrysanthemum were genetically engineered to ectopically express a tobacco (Nicotiana tabacum L.) phytochrome B1 gene under the control of the CaMV 35S promoter. The transgenic plants were shorter in stature and had larger branch angles than wild type (WT) plants. Reduction in growth caused by the ectopic expression of the tobacco phytochrome B1 gene was similar to that caused using a commercial growth retardant at the recommended rate. Another morphological effect observed in the leaves of the transgenic plants was more intense green color that was related to higher levels of chlorophyll. The transgenic plants appeared very similar to WT plants grown under a filter that selectively attenuated far red wavelengths. Furthermore, when plants were treated either with gibberellin A3 (which promoted growth) or 2-chlorocholine chloride, an inhibitor of gibberellin biosynthesis (which inhibited growth) the difference in the average internode length between the transgenic plants and WT plants was the same in absolute terms. This suggests that reduction of growth by the expressed PHY-B1 transgene did not directly involve gibberellin biosynthesis. The commercial application of this biotechnology could provide an economic alternative to the use of chemical growth regulators, thereby reducing production costs.

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Victor Gaba, Chassia Elman, Abed A. Watad, and Dennis J. Gray

Cotyledonary explants of melon (Cucumis melo L. cv. Galia) regenerate primordia and buds in vitro induced by benzyladenine. The anti-gibberellin ancymidol can stimulate the rate of regeneration on melon explants in the presence of benzyladenine. Concentrations of benzyladenine plus ancymidol that are individually ineffective can act synergistically to stimulate regeneration. Gibberellic acid reduces the rate of regeneration induced by benzyladenine or benzyladenine plus ancymidol. Chemical names used: N-(phenylmethyl)-1H-purine-6-amine (benzyladenine); alpha-cyclopropyl-alpha-(4-methoxy-phenyl)-5-pyrimidine methanol (ancymidol).

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Frank G. Dennis Jr. and John C. Neilsen

The evidence for several hypotheses regarding the mechanism(s) controlling biennial bearing in apple (Malus×domestica Borkh.) are reviewed, citing relevant evidence from work with citrus (Citrus sp.) species and pear (Pyrus communis L.). The view that flowering is inhibited by withdrawal of nutrients, primarily carbohydrates, by apple fruit is questionable, given the effects of seed development in inhibiting flowering in facultatively parthenocarpic (normally seedless) apple cultivars. The hypothesis that seeds inhibit flowering by exporting hormones, chiefly gibberellins (GAs), is an attractive one, given a) the effects of application of GAs in inhibiting flowering and b) the high concentrations of GAs in seeds. However, an alternative hypothesis, namely that seeds compete with apices for hormones that are required for flowering, is equally tenable.

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Ria T. Leonard and Terril A. Nell

Several pulse solutions were tested for their effectiveness in preventing leaf senescence on four cut oriental lily cultivars (Lilium sp. `Acapulco', `Kissproof', `Noblesse' and `Star Gazer'). Stems were pulsed 24 hours after harvest for 1 hour, stored in boxes in the dark for 5 days at 3 °C (37.4 °F) then evaluated in postharvest conditions. A new commercial product called Chrysal BVB, a proprietary mixture manufactured by Pokon & Chrysal (Miami) containing cytokinine and gibberellic acids, was the most effective product tested. Chrysal BVB [1 mL·L–1 (0.1%)] prevented leaf chlorosis and abscission on `Acapulco' and `Noblesse' and significantly reduced it by 82% on `Star Gazer' and by 69% on `Kissproof'. Stems pulsed in Fascination, a commercial mixture containing 1.8% gibberellins (GA4+7) and 1.8% benzyladenine [5.4 mg·L–1 (ppm) each], virtually prevented leaf chlorosis on `Noblesse', reduced it by 50% or more on `Acapulco' and `Star Gazer', and significantly delayed it 8 days on `Kissproof'. A 10 μm (2 ppm) pulse in thidiazuron, a substituted phenylurea with cytokinin-like properties, delayed leaf chlorosis on `Star Gazer' but to a lesser extent compared to BVB and Fascination. Chrysal SVB, a propri-etary mixture manufactured by Pokon & Chrysal containing gibberellic acid, had no effect on reducing leaf chlorosis on `Star Gazer'. None of the pulse solutions had adverse effects on bud opening, flower quality or vase life. Maintaining stems in a bulb flower preservative significantly reduced leaf chlorosis and abscission in all cultivars when stems were not pretreated with a pulse solution or when a pulse solution was ineffective.

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M.E. Kane, G.L. Davis, T.D. Hoffner, and R.J. Henny

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B.Z. Escalante and Alan R. Langille

`Katahdin' potato plants were grown under conditions that did not induce tuberization (noninducing conditions) and the foliage was sprayed with either a growth retardant (BAS-111) at 1000 mg·L-1 or distilled water. Other plants, grown under tuber-inducing conditions, received a foliar spray of gibberellic acid (GA3) at 100 mg·L-1 or distilled water. After 1 week, treatments were repeated. Two-node stem segments were excised from the apical, subapical, medial, and basal sections of each plant 72 hours after the second foliar treatment, disinfested, and inserted into flasks containing 50 mL of Murashige and Skoog medium (2% sucrose). After 3 weeks in a darkened incubator adjusted to 24 °C, tuberization response was evaluated. Orthogonal contrasts revealed significant differences between induced and noninduced controls for tuber number, diameter, and fresh mass. BAS-111 reduced rhizome length and increased tuber number, diameter, and fresh mass. GA3 increased rhizome length, but reduced tuber number, diameter, and fresh mass. Node location influenced tuber development, as basal explants produced significantly more and larger tubers, as well as longer rhizomes, than did apical explants, and subapical segments produced more and larger tubers than did apical segments. There were no significant differences between medial and basal nodal segments with respect to tuber number or tuber/rhizome size. Chemical names used: 1-phenoxy-5,5-dimethyl-3-(1,2,4-triazol-1-yl)-hexan-5-ol (BAS-111); 2,4a,7-trihydroxy-1-methyl-8-methylenegibb-3-ene-1,10-carboxylic acid 1->4 lactone (GA3).

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Steven McArtney and John D. Obermiller

technique for stimulating lateral branch development in young sweet cherry trees ( Elfving and Visser, 2009 ; Elfving et al., 2011 ). Elfving and Visser (2007) reported that combining notching with a proprietary formulation of 6-BA plus gibberellin A 4

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Steven J. McArtney and Shao-Hua Li

`Braeburn' apple trees were treated with GA3 or GA7 at either 100, 200, or 400 mg·L-1, 2 years after being grafted onto 4-year-old `Royal Gala'/MM.106 trees in order to evaluate their effects on flower bud formation. Inhibition of flowering was observed on 1-year wood only and not on spurs in response to GA treatments applied later than 6 weeks after bloom. GA7 was a more potent inhibitor of flowering than GA3. These results indicate that GA treatments may provide a useful technology for the selective removal of flowers from 1-year wood in apple and may also provide a useful tool for overcoming biennial bearing in apple by inhibiting flower bud formation when applied in the light-cropping year of the biennial cycle.

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J.W. White, H. Chen, and D.J. Beattie

Aquilegia ×hybrida `Bluebird' and `Robin', grown as greenhouse pot plants, initiated flower buds before cold exposure (4.5C) under supplemental high-pressure sodium lamps in mid-December, 5.5 months from sowing. Low temperature was the primary environmental factor that affected floral development in `Bluebird'. As the length of the cold exposure increased, the time between appearance of visible buds, anthesis, and petal shattering decreased, as did inflorescence number and total flower number per plant. Gibberellic acid (GA3) at 100 or 200 mg·liter-1 accelerated the appearance of visible buds during forcing in treatments without cold exposure. Soil drench applications of GA3 2 weeks before cold treatment accelerated floral development more than GA3 applied after cold exposure. Inflorescence number and total flower number per plant were reduced by 4 or 8 weeks but not by 2 weeks of exposure to cold. The developmental rate of “Robin', i.e., appearance of visible buds and anthesis, was quicker in plants with 18 to 20 leaves than in those with 12 to 14 leaves.

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J.M. Al-Khayri, F.H. Huang, T.E. Morelock, and T.A. Busharar