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Allan M. Armitage

Hamelia patens Jacq. (Texas firebush) is a long-day plant for flower initiation and flower development; however, flower development is more sensitive to photoperiod than is flower initiation. The critical photoperiod for flower development at 25C is between 12 and 16 hours. Flowering was delayed under low light conditions, and plant dry weight was heavier and flowering time was earlier for plants grown at a constant 25 or 30C than at 20C. A greenhouse environment with a 16-hour photoperiod and moderately high temperature (25C) would be appropriate for production of H. patens.

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Mike A. Nagao, Elodie B. Ho-a, and Judy M. Yoshimoto

Flowering of Macadamia integrifolia trees was monitored following application of 220 mg/liter gibberellic acid (GA3) at various times preceding the onset of the flowering season. In untreated trees, flowering extended over a 4-5 month period. When GA3 was applied at 2, 3 and 4 months before the onset of anthesis, raceme production during the entire flowering season was inhibited. A slight reduction in raceme production was observed when GA3 was applied at 1 month preceding anthesis. This application coincided with appearance of the earliest infloresceuces. GA3 application after the onset of anthesis did not alter the flowering pattern of trees during the remaining 4 months of the flowering season. Results suggest that GA3 inhibits flower initiation, but has no effect on raceme emergence after flower bud differentiation has occurred. The relationship between flower initiation and raceme emergence will be discussed.

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Mike A. Nagao, Elodie B. Ho-a, and Judy M. Yoshimoto

Flowering of Macadamia integrifolia trees was monitored following application of 220 mg/liter gibberellic acid (GA3) at various times preceding the onset of the flowering season. In untreated trees, flowering extended over a 4-5 month period. When GA3 was applied at 2, 3 and 4 months before the onset of anthesis, raceme production during the entire flowering season was inhibited. A slight reduction in raceme production was observed when GA3 was applied at 1 month preceding anthesis. This application coincided with appearance of the earliest infloresceuces. GA3 application after the onset of anthesis did not alter the flowering pattern of trees during the remaining 4 months of the flowering season. Results suggest that GA3 inhibits flower initiation, but has no effect on raceme emergence after flower bud differentiation has occurred. The relationship between flower initiation and raceme emergence will be discussed.

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Royal D. Heins

Environmental control computers allow regulation of greenhouse environments based on some model driven factor or factors other than fixed heating and cooling setpoints. A quantitative understanding of how environmental factors influence rate of plant development, flower initiation, and plant morphology is necessary to develop models for environmental control. The major limitation to the use of models for greenhouse climate and crop control is the lack of quantitative models. Examples of model development for environmental control will be discussed.

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Philip G. Schwallier, Paolo Sabbatini, and Martin J. Bukovac

The `Honeycrisp' apple has unique characteristics favored by consumers that has provided exceptional return to growers. This cultivar also has some traits that challenge plant management. There appears to be a strong inhibitory effect of crop load on flower initiation and thus annual cropping. We studied the relationship between fruit load, established by post-bloom hand and chemical thinning, and effect of ethephon and gibberellin (GA4+7) on flower initiation and thereby annual cropping. Initially, return bloom (RB) was related to previous season's crop load in three thinning studies on 3- and 9-year-old `Honeycrisp'/M 9, Pajam 1 trees. The RB density was rated 1–10 on trees (n=172), which produced 0-60 kg of fruit/tree. Return bloom ratings (RBR) on the 3-year-old trees ranged from 0–9. Percentage of trees with RBR >5 for previous season's yield of <5 kg, 5–10, 10–15, and 15–20 was 70, 9, 2.5, and 0, respectively. There was dramatic inhibition of flowering at a crop load of >5 kg/tree. In the second study (9-year-old trees), crop load ranged from 15–60 kg/tree (n=24). RBR for trees in the 30–40 kg/tree class ranged from 0–8 with high variability. Thirty-one percent of trees with crop load between 20–30 kg had RBR of 5–8, and 26% between 0–5. Twenty-one percent of trees in the 30–40 kg/tree class flowered and all but one had a RBR of 5 or less. Yields ranged from 22–81 kg/tree in the third study (n=60); crop load was normally distributed among trees. Flower initiation was almost completely inhibited. Fifty percent of the trees did not flower; the remainder had a RBR of <1, i.e. <10%. In the ethephon/GA study, RBR ranged 8–10 on trees producing <12 kg/tree, then decreased rapidly to <2 for yields of 25–50; greatest variation at 20–40 kg.

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Robert D. Berghage and Royal D. Heins

Elongation characteristics of each internode on a lateral shoot of poinsettia (Euphorbia pulcherrima Klotz) `Annette Hegg Dark Red' were determined from pinching through anthesis for plants grown with 36 day/night temperature (DT/NT) combinations between 16 and 30C. The Richards function was used to describe the elongation of each internode. The first internode developing on a lateral shoot was longer and matured faster than subsequent internodes. The length of the first internode was a function of the difference between day and night temperatures (DIF = DT - NT). Subsequent internodes elongated uniformly in the absence of flower initiation. In the absence of flower initiation, the length of an internode, after the first, was a function of DIF. Internodes were shorter as proximity to the inflorescence increased. Internode length after the start of short days was a function of DIF and the visible bud index where visible bud index = [(days from pinching to the day an internode began to elongate - days from pinching to the day of the start of flower initiation)/the number of days from pinching to visible bud]. A poinsettia lateral shoot elongation model was developed based on the derived functions for internode elongation. The model predicted lateral shoot length within one standard deviation of the mean for plants grown in a separate validation study with 16 combinations of DT/NT. The model allows the prediction of lateral shoot length on any day from pinching through anthesis based on temperature, the number of nodes on the lateral shoot, the time each internode on the lateral shoot began elongating, and the visible bud index at the start of elongation of each node.

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Margaret Pooler and P.W. Simon

Garlic (Allium sativum L.) is an obligate apomict which reproduces almost exclusively by means of division of underground cloves or by propagation of topsets. The occurrence of viable, sexually-derived garlic seeds is rare. In order to assess the factors that limit garlic seed production, variables that affect flower initiation and development were studied. The effects on flowering of daylength, growing temperature, bulb and plant cold storage conditions, and cultivar were examined by observing flower development in plants grown under controlled greenhouse conditions. Correlations between isozyme markers and flowering, fertility, and morphological markers will be presented for a diverse collection of garlic clones, including six sexually-derived garlic plants.

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Richard A. Criley and William S. Sakai

Seasonal flowering behavior of Heliconia wagneriana Petersen was found to be caused by short daylengths (SD) using artificial short days (8 to 9 hours) and long days as daylength extension or night break lighting with incandescent lamps. The natural time for flower initiation was estimated to be mid- to late October (11 hours 40 minutes to 11 hours 20 minutes) in Hawaii, and 120 to 150 days were required from the onset of inductive SD to inflorescence emergence. The results may be used to manipulate flower availability for flower markets.

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R.I. Wilkinson and B. Hanger

Miniature flowering potted Hydrangea macrophylla Thunb. cv. Merritt's Supreme plants (multistem, 15 to 20 cm tall) were grown in a modified hydroponic system. High-quality plants were produced by pulsing plants with paclobutrazol (0.2 mg·liter-1) for 4 weeks. Flower initiation was advanced in the terminal buds of treated plants by 12 days, and this earlier flower development was maintained through to flower maturity, without loss of inflorescence diameter. Chemical name used: β -[(4-chlorophenyl) methyl] -α-(1,1-dimethylethyl)-1 H -1,2,4-triazole-1-ethanol (paclobutrazol, ICI-PP333).

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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.