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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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Li-Chun Huang and Ellen T. Paparozzi

previous studies indicate that there is a significant relationship between the levels of nitrogen and sulfur applied and the growth of floricultural crops. Poinsettia and roses grew well in experiments involving hydroponic solutions that contained reduced nitrogen and some sulfur.

Cuttings of Dendranthema grandiflora cv Dark Yellow Fuji Mefo, were grown in hydroponics with either 64, 127, or 254 ppm N in combination with either 0, 1, 2, 4, 8, 16, 32, 64 ppm S. Plants were grown unpinched and short day treatment started at the end of week 3. Data recorded included symptoms of S deficiency, date of flower initiation, stem length, flower diameter and visual observation of root growth. Color difference of leaves was measured with a chromameter. New leaves and flower heads were taken for sulfur analysis; mature leaves were used for N analysis.

Plants receiving no S showed depressed initiation and development of branch roots, delayed flower initiation, reddened lower leaves and reduced plant growth. Plants receiving some S in combination with any level of N showed good color and acceptable flower diameter and stem length.

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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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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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Caroline J. Poole, Audrey I. Gerber, and Gerard Jacobs

Brunia albiflora (Pillans) is harvested commercially in South Africa as a cut flower for export to European markets. To compete with European cut flowers high quality and continuity of product during the marketing period are essential. Optimizing the cut-flower potential of B. albiflora requires an understanding of the flowering process and selection of clonal material. We present a series of scanning electron micrographs which show three-dimensional images of the developmental stages of the shoot apex during the transition from the vegetative to the reproductive state. In B. albiflora the inflorescence consists of more than 15 individual rotund inflorescences arising from lateral positions on the terminal portion of the shoot. Development of the apical meristem of axillary shoots was studied to determine the time and sequence of inflorescence initiation and development. These observations identified that flower initiation occurs in October, followed by flower development through summer, with anthesis being reached from February to March.

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Theo J. Blom and Brian D. Piott

Four freesia cultivars were exposed to 24 hour·day-1 high-pressure sodium (HPS) lighting during various stages of their development. Upon emergence, freesia plants were exposed to the following four lighting treatments: 1) ambient; 2) ambient until shoot length was 5 to 8 cm followed by HPS lighting until flowering; 3) HPS lighting until shoot length was 5 to 8 cm followed by ambient lighting; and 4) continuous HPS lighting. Supplemental HPS lighting was provided at 37 μmol·m-2·s-1 at plant level in a glasshouse. Continuous lighting or lighting during flower development hastened flowering but reduced the number of flowering stems per corm, as well as stem length and weight. Lighting during the vegetative and flower initiation periods produced minor effects. The main benefit of supplemental lighting was found in total corm weight.

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Abraham H. Halevy, Eitan Shlomo, and Ofra Ziv

Experiments aiming to adapt the perennial balloon flower (Platycodon grandiflorus) as a commercial cut flower crop were conducted for 4 years under various growing conditions: four controlled-temperature rooms at two photoperiods in a phytotron, heated and unheated greenhouses, and a saran net-house (15% shade). Best flower yield was obtained following crown cooling for 12 weeks at 2 to 4 °C. Platycodon is a day-neutral plant, but produce more flowering stems under long days. Flower initiation and development is enhanced with increased growing temperature from 17/12 °C (day/night) to 27/22 °C. At very high temperatures (32/24 °C), however, only a few flowers are formed. Best quality stems were produced at 12 to 14 °C night temperature. At higher night temperatures, flowering stems were thin and weak. Gibberellin treatments to the crowns and the plants did not affect flowering time. Chemical name used: gibberellin (GA3).