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Meriam G. Karlsson and Janice T. Hanscom

The progression of flower initiation was documented in Dendranthema X grandiflorum (Ramat) Kitamura `Bright Golden Anne'. Rooted cuttings were planted and grown under 16 hours photoperiod (360 μmol·s-1m-2) and a constant 20C. After 7 days, the plants were pinched, the temperature reduced to 5, 10 or 15C and the day length shortened to 10 hours (13 mol·day-1m-2). Scanning electron microscopy was used to determine the transition from vegetative to reproductive meristem and to document the flower formation process. Shoot apices from three randomly selected plants were dissected weekly from each temperature until plants had developed floret primordia to completely cover the apical dome. Delayed floral development in the low temperature grown plants was a combination of a later flower initiation event and a slower progression of flower development. Required time for formation of 3-4 rows with floret primordia was about 21 days at 15C, 32 days at 10C and 70 days at 5C.

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Warner Orozco-Obando* and Hazel Y. Wetzstein

The general doctrine of flowering in Hydrangea is that floral induction occurs during the previous season on last year's growth and usually at the stem's terminal bud. However, Hydrangea cultivars widely differ in their relative abundance and duration of flower production. The objective of this study was to determine how developmental flowering patterns compare among different genotypes. Flowering was characterized in 18 H. macrophylla cultivars by assessing the extent of flower initiation and development in terminal and lateral buds of dormant shoots (i.e., after they have received floral inductive conditions.) Plants were managed under outdoor conditions. Dormant, 1-year-old stems were collected and characterized for caliper and length. All buds >2 mm were dissected and the vegetative or floral bud stage of development was categorized for each bud microscopically. Flower development occurred in 100% of the terminal buds for all the cultivars with the exception of `Ayesha' (33%). In contrast, lateral buds showed a wide variation in flower development. For example: `All Summer Beauty', `David Ramsey', `Kardinal', `Masja', and `Nightingale' showed high levels of floral induction (>92 % of lateral buds induced.) In contrast, `Ayesha', `Blushing Pink', `Freudenstein', and `Nigra' had 10% or fewer lateral buds with floral initials. Thus, the degree of floral induction in lateral buds varied tremendously among different cultivars. In addition, flower initiation and development were not related to the size (length and caliper) of individual buds. Thus, bud size does not appear to be a good indicator of flowering potential.

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Gretchen E. Mills and Allen V. Barker

For optimum plant growth in containers, adequate plant nutrition is essential. Objectives of this research were to determine the optimum fertilization of tomatoes (Lycopersicon esculentum Mill.) in a peatbased medium and to assess plant nutrition by plant and media analysis. Tomato seedlings ('Heinz 1437') were transplanted (one plant per pot) into 2-L pots filled with a peat-based medium. The medium was fertilized with a progressive array of soluble fertilizers to supply N at 0, 50, 100, 150, or 200 mg·L-1 of solution with concomitant proportional increases of other macronutrients with each increase in N (P at 0, 10, 20, 30, or 40; K at 0, 40, 80, 120, or 160; Ca at 0, 50, 100, 150, or 200; and Mg at 0, 12, 24, 36, or 48 mg·L-1). The plants were irrigated starting with 100 mL fertilizer solution per day and increasing to 200 mL per day as plant growth progressed. The tomatoes were harvested at three stages of growth (five-leaf stage, flower initiation, and fruit initiation) for analysis of growth and composition. Samples of media for nutrient analysis were taken at each growth stage. Plant biomass increased linearly as fertilizer level increased or as time progressed. Generally, concentrations of nutrients in the medium increased linearly with increases in nutrients in the solutions. With time, N concentrations in media rose, but P, K, Ca, and Mg in the media fell. Concentrations of N, P, or K in leaves increased as nutrition increased, but Mg or Ca in leaves had no significant changes with increased nutrient supply. The N, P, Ca, and Mg in tissues fell, but K rose with time. Assessment of plant nutrition was best at flower initiation, with assessments at the other stages of development being judged as untimely or excessively variable. For optimum growth, critical concentrations of nutrients in the media (mg·kg-1) at flower initiation were judged to be 30 NO3-N, 30 P, 300 K, 2600 Ca, and 800 Mg and in leaves (g·kg-1) to be 35 N, 10 P, 70 K, 35 Ca, and 20 Mg. Optimum fertilization to reach these critical concentrations was reached with the third level (the regime with 100 mg N/L) or higher levels of nutrition.

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Z. Wang, M.C. Acock, Q. Liu, and B. Acock

Flowering time, growth, and opium gum yield from five seed sources (T, L, B1, B2, B3) of opium poppy (Papaver somniferum L.) collected from different latitudes in three Southeast Asian countries were determined. Plants were grown in six growth chambers at a 11-, 12-, 13-, 14-, 15-, or 16-hour photoperiod with a 12-hour, 25/20 °C thermoperiod. Flower initiation was observed under a dissecting microscope (40×) to determine if time to floral initiation was identical for all accessions across a wide range of photoperiods. The main capsule was lanced for opium gum at 10, 13, and 16 days after flowering (DAF). Plants were harvested at 21 DAF for plant height, leaf area, and organ dry-weight determinations. In a 16-hour photoperiod, flower initiation was observed 10 days after emergence (DAE) for B1 vs. 8 DAE for the other four accessions. Flowering time was affected most by photoperiod in B1 and least in B2. Flowering times for B3, L, and T were similar across the range of photoperiods. B2, B3, and L had the highest gum yields per capsule; even though B1 had the greatest total plant biomass, it produced the lowest gum yield. There was no difference among accessions in the average ratio of gum: individual capsule volume. For the ratio of gum: capsule dry weight, only the difference between T and B1 was significant. Capsule size did affect these ratios slightly. T had a larger gum: volume ratio for larger capsules, and B3 had a smaller gum: dry-weight ratio for heavier capsules. Flowering time varied up to 40%, capsule dry weight up to 41%, and opium gum yield up to 71% for the five accessions across all treatments. No relationship was found between flowering time and the latitude where the seed sources were collected. Time to flower initiation could not be used to predict time to anthesis because floral development rates varied significantly among accessions and photoperiods. Capsule volume and dry weight were useful in estimating gum yield.

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Teryl R. Roper and Marianna Hagidimitriou

Carbohydrate concentration may be important for flower initiation and fruit set in cranberry (Vaccinium macrocarpon Ait.). Fruit set has been shown to be a major limiting factor in yield component analysis. The objective of this research was to identify carbohydrate concentrations in cranberry tissues at various stages of development under field conditions. Samples of two cranberry cultivars, `Stevens' and `Searles' were collected during the 1989 season using a 13 cm diameter probe. Samples were divided into fruit, uprights, woody stems and roots. Carbohydrates were quantified by HPLC. Nonstructural carbohydrates were primarily sucrose, glucose, fructose and starch. Soluble carbohydrate concentration was stable throughout the season in tissues analyzed, while starch content was high early in the season then decreased during blossom and fruit set. This work shows that starch reserves in leaves and stems apparently are remobilized to support fruit set in cranberry.

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Jens J. Brondum and Royal D. Heins

Dahlia “Royal Dahlietta Yellow” plants were grown in controlled temperature chambers under 25 different day and night temperature environments ranging from 10°C to 30°C. The day length was 12 hours with an average PPF level of 300 micromolm-2 s-1 at canopy level. Leaf unfolding rate, shoot elongation and flower development rate were determined and models developed. Leaf unfolding rate increased as temperature increased up to 25°C. Stem elongation increased as the difference between day and night temperature increased. Flower initiation was delayed at high (30°C) temperature and flower development rate increased as temperature increased from 10°C to 25°C. Plants are currently being grown under greenhouse conditions to provide data for validating the models.

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D. Zhang, A.M. Armitage, J.M. Affolter, and M.A. Dirr

Dense-flowered loosestrife is a quantitative long-day (LD) plant. Plants given a LD photoperiod (16 hours) flowered 21 and 34 days earlier than plants given 12- and 8-hour photoperiods, respectively. Plants under LDs produced significantly more flowers than those under 8- and 12-hour photoperiods. Only 1 week of LD was needed for 100% flowering; however, optimum flower count and size were produced with 3 weeks of LD. Plant dry weight did not differ significantly among treatments; however, LDs produced fewer but larger leaves, particularly those subtending the inflorescence. Total plant growth increased as temperature increased, but lower temperature (10C) decreased flower initiation and prevented flower development. High temperature (26C) reduced the persistence of open flowers. The optimum temperature for dense-flowered loosestrife growth was ≈20C. Flowering was accelerated and dry weight production increased as irradiance levels increased from 100 to 300 μmol·m–2·s–1.

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L-Y. Li, J.H. Lieth, R.H. Merritt, and H.C. Kohl

A heat-unit model was established for tracking the development of geranium, based on experimental data collected at UC Davis and Rutgers Univ. The temperature thresholds for initiating development and heat-unit benchmarks needed to accomplish each phenostage are parameters in this model. The methods of estimating these parameters were proposed and tested with the observed data. The model worked well during either vegetative or reproductive stages, but failed to predict the initiation of flowers, suggesting that factors other than only temperature drive the flower initiation process. With this model crop development characterized by a series of specific morphological events can be tracked and predicted under various temperature regimes, so that crop timing can be more precise.

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Michael J. Roll and Steven E. Newman

The rooting efficiency of cuttings from three poinsettia cultivars were evaluated after regulating the photoperiod during the stock plant stage. `Freedom Red', `Monet', and `V-17 Angelika Marble' stock plants were exposed to an extended photoperiod and to natural day length during September 1995. `Freedom Red' cuttings rooted more quickly under an extended photoperiod compared to those under natural day length. Furthermore, root dry weight from these cuttings was greater than cuttings from stock plants grown under natural day length. `Monet' cuttings also rooted more quickly when the stock plants were under an extended photoperiod, and showed similar differences in root weight as `Freedom Red'. Cuttings from `V-17 Angelika Marble' were not influenced by photoperiod. Lighting stock plants to block flower initiation produces a higher quality cutting when propagation takes place after the critical day length for flowering has passed.

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A. Belakbir, J.M. Ruiz, and L. Romero

To test the effectiveness of different bioregulators in enhancing bell pepper (Capsicum annuum L.) yield and fruit quality, the commercial bioregulators CCC, NAA, GA3, and Biozyme® were sprayed on plants at flower initiation, followed by two additional applications at 30-day intervals. Biozyme produced a significant increase in total yield but ≈40% of the fruit were not marketable. Treatment with NAA produced the highest yield of marketable fruit. Treatments did not affect fruit firmness compared to the control. Gibberellic acid increased fruit ascorbic acid and citric acid concentrations and Biozyme, GA3, and CCC increased fruit soluble solids content. Biozyme treatment increased fruit fructose, sucrose, carotenoid, and lycopene concentration. Treatments had no effect on fruit calcium concentration or pH. Chemical names used: chlormequat chloride (CCC); naphthaleneacetic acid (NAA), gibberellic acid (GA3); GA3 + IAA (indoIe-3-acetic acid) + zeatine + micronutrients (Biozyme®).