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  • Author or Editor: R.D. Heins x
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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

The objective was to predict the distribution (mean and variance) of flower opening for an Easter lily (Lilium longiflorum Thunb.) population based on the variability in an earlier phenological stage and the expected average temperature from that state until flowering. The thermal time from the visible bud stage until anthesis was calculated using published data. `Nellie White' grade 8/9 Easter lilies were grown in five research and commercial greenhouse locations during 1995, 1996, and 1997 under a variety of temperature and bulb-cooling regimes. Distributions of visible bud and anthesis were normally distributed for a population growing in a greenhouse with spatially homogenous temperatures. The variance at anthesis was positively correlated with variance at visible bud. The mean and variance at visible bud could therefore be used to predict the distribution of the occurrence of anthesis in the crop. The relationship between bud elongation, harvest, and temperature was also incorporated into the model. After visible bud, flower bud length measurements from a random sample of plants could be used to predict the harvest distribution. A computer decision-support system was developed to package the model for grower use.

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A model was developed to quantify the response of Easter lily (`Nellie White') flower bud elongation to average air temperature. Plants were grown in greenhouses set at 15, 18, 21, 24, or 27C after they had reached the visible bud stage. An exponential model fit the data with an R 2 of 0.996. The number of days until open flowering could be predicted using the model because buds consistently opened when they were 16 cm long. The model was validated against data sets of plants grown under constant and varying greenhouse temperatures at three locations, and it was more accurate and mathematically simpler than a previous bud elongation model. Bud length can be used by lily growers to predict the average temperature required to achieve a target flowering date, or the flowering date at a given average temperature. The model can be implemented in a computer decision-support system or in a tool termed a bud development meter.

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Two fungicides registered for the control of Pythium spp. were evaluated for their effects on size and time to flowering of seed-propagated geraniums (Pelargonium × hortorum L.H. Bailey). Fungicide drenches of fenaminosulf and metalaxyl were applied to geraniums grown in soilless root medium: 1) at seeding (S); 2) at seeding and transplanting (ST); 3) at seeding, transplanting, and 1 week after transplanting (ST + 1); 4) at transplanting (T); and 5) 1 week after transplanting (T + 1). Metalaxyl drenching schedules did not significantly influence plant size or time to flowering. Fenaminosulf drenching schedules 3 and 4 significantly reduced plant size, and drenching schedule 3 significantly increased days to flowering in comparison to control plants. Although fenaminosulf is used infrequently because of limited availability, the detrimental effects of this fungicide on plant size and time to flowering warrant similar investigations with additional fungicides and crops. Chemical names used: sodium[4-(dimethylamino) phenyl]diazenesulfonate (fenaminosulf); N-(2,6-dimethylphenyl) -N-(methoxyacetyl) -dl-alanine methyl ester (metalaxyl).

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Our objective was to quantify the stem-elongation patterns of several Oriental and Asi-florum lily cultivars to develop graphical tracking charts where actual crop height can be compared visually against a target growth curve. Oriental lilies (`Mona Lisa' and `Stargazer') were grown in research greenhouses at Michigan State Univ. (MSU) during 1994 and 1995. Asi-florum lily cultivars (`Centurion', `LA-87', `Non-stop', `Salmon Queen', and `Salzburg') were grown at MSU in 1995. Plants received constant 20 °C from emergence to flower in 1995, and constant 15, 18, 21, 24, or 27 °C in 1994. Elongation of Oriental lily plants followed a sigmoid pattern. Oriental lily cultivars elongated rapidly after emergence until 60% of the relative time between dates of emergence and first open flower, at which time plants had achieved ≈82% (`Stargazer') or 85% (`Mona Lisa') of their final height; elongation then exhibited a plateau phase. In contrast to the Oriental lilies, Asi-florum cultivars consistently exhibited a more constant elongation rate throughout the growing period. Simplified graphical tracking curves were developed based on the patterns of elongation and were programmed into a computer decision—support system (`UNH FloraTrack'). The graphical tracking curves were tested by growing `Stargazer', `Mona Lisa', and four Asiflorum cultivars (`Donau', `Dream', `Moneymaker', `Spirit') at the Univ. of New Hampshire and MSU during 1997 to height specifications of 51 to 56 cm (including a pot height of 15 cm). Sumagic growth retardants were applied as a prebulb dip at 5 ppm and as a foliar spray at 3 ppm when plant height was above the target curve. Final height targets were achieved using this method. E-mail prf@hopper.unh.edu; phone, (603) 862-4525.

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Abstract

Night irradiation of stock plants and cuttings during the rooting period with red (R) or incandescent (INC) light resulted in statistical differences in rooting of cuttings of chrysanthemum (Chrysanthemum morifolium Ramat. cvs. Bright Golden Anne and Mrs. Roy) but differences were not large enough to be of commercial concern. Rooting was best when stock plants were irradiated with R light and cuttings were subsquently rooted under INC light and poorest when cuttings from INC irradiated stock plants were rooted under R light.

Open Access

Abstract

Plants of chrysanthemum (Dendranthema grandiflora Tzvelev.) were grown under one of 25 irradiance and temperature combinations from start of short days to flower. Four phases of development were defined as 1) the start of short days to the appearance of 4-mm terminal flower buds (phase I), 2) appearance of 4-mm terminal flower buds to removal of lateral flower buds when the terminal flower bud was 7 to 8 mm (phase II), 3) removal of lateral flower buds to flower buds showing first color (phase III), and 4) flower buds showing color to flowering (phase IV). Path analysis was used to study the influence of development time and relative dry weight gain during each of these four phases on development time and relative dry weight gain of subsequent phases. Relative dry matter accumulation during phases I, II, III, and IV significantly influenced cumulative relative dry weight gain, with phase I having the greatest influence. Increasing relative dry weight gain during phase I had a significant negative effect on relative dry weight gain in phase II. Time within each phase significantly affected total time to flower. Under the constant environmental conditions of this experiment, time in one phase did not influence the length of time in later phases.

Open Access

Abstract

Chrysanthemum morifolium Ramat. ‘Bright Golden Anne’ cuttings were grown in a controlled environment at 50, 325, or 600 µmol·s–1·m–2 for 5 weeks at a 10-hr photoperiod. Photosynthetic rates were determined on individual leaves with an open gas analysis system at a range of photosynthetic photon flux (PPF) levels. Plants grown at low PPF (50 µmol·s–1·m–2) had a maximum net photosynthetic rate (Pn) that was about 39% of that for plants grown at 325 µmol·s–1·m–2. Pn of plants grown at 325 or 600 µmol·s–1·m–2 did not differ significantly.

Open Access