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  • Author or Editor: R.D. Heins x
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A graphical control chart was developed to monitor leaf count of Easter lily (Lilium longiflorum Thunb.) and make temperature recommendations based on predictions of a leaf unfolding rate (LUR) model. The graph allows observed and target leaf count to be compared visually over time. Timing of the visible bud stage, when flower buds are visible externally on the plant, is important to time flowering for the Easter sales period. The optimum LUR and average daily temperature required to achieve a target visible bud date can be read directly from the chart. The approach provides an intuitive method for transferring quantitative models to growers.

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A methodology based on process-control approaches used in industrial production is introduced to control the height of poinsettia (Euphorbia pulcherrima L.). Graphical control charts of actual vs. target process data are intuitive and easy to use, rapidly identify trends, and provide a guideline to growers. Target reference values in the poinsettia height control chart accommodate the biological and industrial constraints of a stemelongation model and market specifications, respectively. A control algorithm (proportional-derivative control) provides a link between the control chart and a knowledge-based or expert computer system. A knowledge-based system can be used to encapsulate research information and production expertise and provide management recommendations to growers.

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Abstract

In the paper, Influence of Photoperiod and Light Quality on Stolon Formation and Flowering of Chlorophytum comosum (Thunb.) Jacques by R. D. Heins and H. F. Wilkins (J. Amer. Soc. Hort. Sci. 103(5):687-689. 1978), the authors names were inadvertently omitted from the table of contents.

Open Access

A stem elongation model is being developed for pinched poinsettia crops as part of a decision support computer program, the `Greenhouse CARE System'. Internode elongation is modelled as a function of DIF (day minus night temperature), plant density, and growth retardant applications. Average daily temperature and flower initiation date are used to determine internode number. Dose response curves are being developed to describe internode response to growth retardant applications, as affected by chemical type, concentration, time of application, and application method. The impact of plant density on growth and development is being modelled, and a spectroradiometer is being used to measure the effect of neighbouring plants on the light quality and quantity surrounding an individual plant. The model takes into account cultivar differences in their response to growth retardants and plant density. Output from the model is used to predict the short-term change in plant height under commercial greenhouse conditions. An interactive graphical interface to the model allows the comparison of alternative height control strategies.

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Impatient hawkeri Bull. cv `Mimas' rooted cuttings were planted in 15.2 cm plastic pots and were placed in glasshouses maintained at 15, 20, 25, or 30C. Plants were rotated among glasshouses at 0800 and 1700hr each day (9 hr photoperiod) to yield 16 different day/night temperature (DT/NT) regimes. Data were collected on time of first flower, internode length, stem calibre, flower diameter, leaves per node, individual leaf area, and the dry weight of the leaves, stem, and flowers on a representative shoot from each plant. Morphology data were collected after 80 days. Plants grown at 15C required 27 more days to flower than plants grown at 30C. Internode length increased as the difference (DIF) between DT and NT (DT-NT) increased and as temperatures approached 25C. Stem calibre was unaffected by temperature. Flower diameter had an optimal temperature of 20C. Leaves per node and leaf area had optimal temperatures of 25C. Stem dry weight increased as DIF increased. Flower dry weight was greatest when plants were grown at constant 20C. Shoot and leaf dry weight were greatest in the 25 DT/15C NT regime.

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Abstract

Differences in cyathia abscission of poinsettias (Euphorbia pulcherrima Willd.) ‘Annette Hegg Dark Red’ (Dark Red), ‘Annette Hegg Lady’ (Lady), ‘Annette Hegg Brilliant Diamond’ (Brilliant), ‘Gutbier V-14 Glory’ (V-14), and ‘Mikkel Triumph’ were evaluated chronologically based both on the number of days after the start of short days and on the number of days after anthesis. Seventy days after the start of short days, ‘V-14’ had the least abscission of the tested cultivars in the greenhouse or postharvest environment, while ‘Lady’ had the greatest abscission. In contrast, 7 days after anthesis, ‘V-14’ had the greatest abscission in the postharvest environment while ‘Brilliant’ and ‘Dark Red’ had the least abscission. The difference in ‘V-14’ ranking between evaluation method was due to ‘V-14’ reaching anthesis 7-10 days later than the other cultivars. Abscission was greater in the postharvest environment than in the greenhouse, probably due to the reduced photosynthetic photon flux (PPF) levels in the postharvest environment (5.1 mol·d−1·m−2 PPF in the greenhouse compared to 0.29 mol·d−1·m−2 PPF in the postharvest environment).

Open Access

Abstract

Low irradiance levels, high temperatures, and water stress all promoted premature cyathia abscission in poinsettia ‘Annette Hegg Dark Red’ (Euphorbia pulcherrima Willd.). Abscission was greater in plants placed under 75% shade at 16°C night temperature (NT) than on plants placed under normal daylight (ND) at 16° or 21° NT. Water stress (0.6 MPa) promoted abscission on plants grown at an 18° NT and ND but did not promote abscission on plants grown at 16° NT and ND or on under 75% shade (13° to 21° NT). As plant density increased, transmission of photosynthetically active radiation (PAR) through the bracts to the leaf canopy decreased while cyathia abscission increased concomitantly. More than 90% of the PAR above the bracts was absorbed or reflected 5 cm below the bracts on 20 cm tall plants spaced at 65 or more plants m-2. Reducing natural irradiation 75% by shading leaves of poinsettia promoted cyathia abscission, whereas removing immature bracts decreased abscission. Leaf removal on plants with intact bracts promoted abscission to a degree that 100% of the cyathia abscised prior to anthesis, whereas bract removal on plants with intact leaves resulted in only 23% abscission of the cyathia 25 days after first anthesis. Measurements of nonsoluble carbohydrate showed a significant increase in leaf carbohydrate on plants with bracts removed while carbohydrate decreased in leaves of plants with bracts intact. Carbohydrate depletion appears to be the primary factor responsible for premature cyathia abscission in poinsettia.

Open Access
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Abstract

Chrysanthemum morifolium Ramat. ‘Bright Golden Anne’ plants were grown under 15 combinations of photosynthetic photon flux (PPF), day temperature, and night temperature in a central composite design. Time to flower was a function of both irradiance and the interaction between day and night temperature. The surface response to temperature was bowl shaped with delayed development as temperatures were either increased or decreased from the optimum combinations. High temperature delay was compensated for in part by increased PPF. Shoot length increased linearly as day temperature increased; final shoot length first decreased, then increased with increasing night temperature. The response surface appeared as a rising valley with the longest shoot lengths at high day temperatures. Total flower area per plant increased as PPF increased or as night temperature decreased. For any PPF and night temperature, maximum flower area occurred near 20°C. At a constant PPF, the response surface appeared as a rising ridge with maximum flower area at low night temperature.

Open Access
Authors: and

Abstract

Plants of Chrysanthemum morifolium Ramat. cv. Bright Golden Anne irradiated as a day continuation or night interruption with light from cool white fluorescent tubes wrapped with red cellophane (red) produced more cuttings than plants irradiated with incandescent light. There were no significant differences in cutting production when plants were irradiated just prior to dawn. Increased cutting production from plants irradiated with red light was attributed to increased axillary bud activity, especially at the middle nodal position. When shoots were pruned to 4 or 8 nodes, the apical axillary bud produced the maximum number of cuttings and the basal produced the minimum, irrespective of light quality or time span of irradiation.

Open Access