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Bruce W. Wood

understanding of floral initiation processes operating in pecan. This study assesses certain promising bioregulators for activity and/or influence on pecan flowering and examines how their interactions influence pistillate flower initiation. It reports that

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

Floral initiation in coffee has been shown to be stimulated by short days in young plants, but the inductive stimulus for mature plants is still not clear. Experiments were conducted to determine whether floral initiation in immature and mature plants is promoted by short photoperiods, and delayed by long photoperiods. In a growth chamber study, 18-month-old coffee (Coffea arabica L. cv. Guatemalan) plants exposed to 8 hr photoperiods developed flower buds after 4 weeks, whereas no floral initiation was observed on the plants exposed to 16 hr photoperiods for ten weeks. Trees growing in the field were illuminated with incandescent light from midnight to 3:00 a.m. from July to December 1989. The control plants received no artificial light during the same time period. Night light interruption delayed flower initiation until the end of December on branches that were fully exposed to the light. On control trees, flower buds started to emerge at the beginning of November. These results indicate that in immature and mature coffee plants floral initiation is stimulated by short days, and delayed by long days.

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P.R. Fisher, J.H. Lieth, and R.D. Heins

Stem elongation of commercially produced flowering poinsettia (Euphorbia pulcherrima L.) is often sigmoid. However, sigmoid mathematical functions traditionally used for representing plant growth fail to adequately describe poinsettia stem elongation when a shoot has a long vegetative growth period. A model was developed that explicitly described three phases of poinsettia stem elongation: 1) the initial lag phase, where stem length increases approximately exponentially; 2) a period when elongation is linear; and 3) a plateau phase, where elongation rate declines to zero and stem length reaches an asymptotic maximum length. The timing of the plateau phase was linked to flower initiation date. Fit of the resulting model to data from single stem `Freedom' poinsettia grown with different periods between transplant and flower initiation had an R2 of 0.99. Model parameters had clear biological meaning, and the poinsettia model has horticultural application for simulation and graphical tracking of crop height.

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Paul R. Fisher, Royal D. Heins, and J. Heinrich Lieth

Stem elongation of poinsettia (Euphorbia pulcherrima Klotz.) was quantified using an approach that explicitly modelled the three phases of a sigmoidal growth curve: 1) an initial lag phase characterized by an exponentially increasing stem length, 2) a phase in which elongation is nearly linear, and 3) a plateau phase in which elongation rate declines as stem length reaches an asymptotic maximum. For each growth phase, suitable mathematical functions were selected for smooth height and slope transitions between phases. The three growth phases were linked to developmental events, particularly flower initiation and the first observation of a visible flower bud. The model was fit to a data set of single-stemmed poinsettia grown with vegetative periods of 13, 26, or 54 days, resulting in excellent conformance (R 2 = 0.99). The model was validated against two independent data sets, and the elongation pattern was similar to that predicted by the model, particularly during the linear and plateau phases. The model was formulated to allow dynamic simulation or adaptation in a graphical control chart. Model parameters in the three-phase function have clear biological meaning. The function is particularly suited to situations in which identification of growth phases in relation to developmental and horticultural variables is an important objective. Further validation under a range of conditions is required before the model can be applied to horticultural situations.

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Christine Yung-Ting Yen, Terri W. Starman, Yin-Tung Wang, Andreas Holzenburg, and Genhua Niu

cultivar Pendragon Sikkim of a Cymbidium Sw. hybrid, nutrient application was suggested to be ended before flower initiation began for increased inflorescence/shoot ratio along with earlier flowering ( Arnold Bik and van den Berg, 1983 ). For

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Min Lin, Terri W. Starman, Yin-Tung Wang, and Genhua Niu

cooled in complete darkness to induce flower initiation. Additional research is needed to obtain more data to study if induction in darkness or under low PPF would negatively impact flower quality of the nobile dendrobium. The objective of this study

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Martin J. Bukovac, Paolo Sabbatini, Franco Zucconi, and Phillip G. Schwallier

development ( Jackson and Hamer, 1980 ) and the tendency was greater in spur- than nonspur-type trees ( Jonkers, 1979 ; Monselise and Goldschmidt, 1982 ). Early defoliation in “on” years, within 6 weeks after bloom, reduced flower initiation ( Aldrich and

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Michael Alden and James E. Faust

Poinsettia is a short-day plant that begins to initiate flowers around the time of the autumnal equinox (21 Sept.) when NLs become sufficiently long and thereby inductive ( Ecke et al., 2004 ). Flower initiation can be delayed by exposure to supra

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Michael J. Roll and Steven E. Newman

Rooting of cuttings from three cultivars of Euphorbia pulcherrima Willd. was evaluated after regulating the photoperiod during the stock plant stage. One group of stock plants was exposed to a night break (4 hours) and another group was exposed to natural daylength during September. Cuttings harvested in late September from `Freedom Red' and `Monet' stock plants grown under the 4-hour night break rooted more rapidly and had greater root mass than `Freedom Red' and `Monet' grown under natural daylength, whereas rooting of cuttings from `V-17 Angelika Marble' was not influenced by the photoperiods tested. Using a night break to prevent flower initiation of stock plants produced a higher-quality cutting when propagation took place after the critical daylength for flowering had passed.

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Mark P. Kaczperski and Royal D. Heins

Plug-grown Pelargonium × hortorum `Pinto Red' seedlings were grown under natural daylight (average of 4.7 mol/day) or with supplemental irradiance from high-pressure sodium lamps. Seedlings were grown under 8-, 16-, or 24-h photoperiods with supplemental irradiances of 2.5, 3.75, or 5.0 mol/day at each photoperiod. Supplemental irradiance was provided for 7, 14, 21, and 28 days beginning 7, 14, 21, 28, and 35 days after sowing. Seedlings were transplanted 63 days after sowing to 8-cm containers (121 plants/m2) and grown to flower. Leaf number at time of transplant was not affected by photoperiod, but increased as daily irradiance and weeks of supplemental irradiance increased. Seedlings were more responsive to supplemental irradiance applications beginning 28 and 35 days than at 7 to 21 days after sowing. Ninety-two percent of seedlings receiving 28 days of 5.0 mol/day supplemental irradiance under a 24-h photoperiod starting 35 days after sowing had initiated flower buds at time of transplant; 75% of those receiving 3.75 mol/day were initiated. Plants receiving less than 3 weeks of supplemental irradiance or with an irradiance period beginning less than 28 days after sowing had not initiated flowers at transplant.