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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.
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).
Stem elongation of poinsettia (Euphorbia pulcherrima Klotz.) was quantified using an approach that explicitly modelled the three phases of a sigmoidal growth curve: 1) an initial lag phase characterized by an exponentially increasing stem length, 2) a phase in which elongation is nearly linear, and 3) a plateau phase in which elongation rate declines as stem length reaches an asymptotic maximum. For each growth phase, suitable mathematical functions were selected for smooth height and slope transitions between phases. The three growth phases were linked to developmental events, particularly flower initiation and the first observation of a visible flower bud. The model was fit to a data set of single-stemmed poinsettia grown with vegetative periods of 13, 26, or 54 days, resulting in excellent conformance (R 2 = 0.99). The model was validated against two independent data sets, and the elongation pattern was similar to that predicted by the model, particularly during the linear and plateau phases. The model was formulated to allow dynamic simulation or adaptation in a graphical control chart. Model parameters in the three-phase function have clear biological meaning. The function is particularly suited to situations in which identification of growth phases in relation to developmental and horticultural variables is an important objective. Further validation under a range of conditions is required before the model can be applied to horticultural situations.
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.
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).
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.
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.
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.
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.
Abstract
Alstroemeria ‘Regina’ plants produced more vegetative shoots when the soil temperature alternated between 15°C (40 days) and 21° (20 days) as compared to a constant 15° soil temperature. However, a higher percentage of the shoots flowered from plants grown at the constant 15° soil temperature. Short days (8 hours light) inhibited flowering irrespective of soil temperature. Plants given a long-day treatment by exposing them to a night break with incandescent light flowered 6 weeks earlier than plants grown under normal day photoperiods during winter and spring and produced 30% more flowering stems. Treatments favoring flower development produced shorter flowering stems with fewer leaves. Maximum flower production resulted from plants grown at a constant 15° soil temperature and irradiated with incandescent lights as a night interruption.