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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
Long photoperiods (either naturally long days or 4-hour night interruptions with low intensity incandescent light) inhibited lateral shoot development and induced early flowering in perpetual flowering carnation (Dianthus caryophyllus). Short photoperiods delayed flowering but enhanced lateral shoot development only when shoots were vegetative. Once a shoot was induced, short photo periods had no influence on time to terminal shoot flower or on subtending vegetative lateral shoot development. Vegetative lateral shoot development was inhibited by night interruption lighting regardless of light source. These data indicate that high flower production in Spring and summer is due to lateral vegetative shoots which begin elongation and growth during the non-flower inductive short days of winter. At higher latitudes low production of flowers may not entirely be due to low photo-synthetic light but to the low number of lateral shoots. This low number of potential flowering shoots is due to highly inductive long days of summer which have caused shoots to flower before subtending lateral shoots can begin growth for future flower production.
Abstract
The rate of leaf unfolding was determined for Easter lily (Lilium longiflorum Thunb.) ‘Nellie White’ grown at day and night temperatures ranging from 14° to 30°C. In this temperature range, rate of leaf unfolding was a linear function of average daily temperature; i.e., the effect on rate of leaf unfolding for day temperature was the same as for night temperature. The function determined was: leaves unfolded per day = −0.1052 + (0.0940 × average daily temperature). Isopleth plots were developed to describe day and night temperatures required for specific rates of leaf unfolding under 8-, 10-, and 12-hr day temperature periods.
Abstract
Alternanthra amoena Voss, Coleus × hybridus Voss., Hedra helix L., Pelargonium × hortorum Bailey, Peperomia obtusifolia L.,Pilea cadierei Gagnep. & Guillaum, Pilea ‘Moon Valley’ and Pilea involucrata ‘Panamegia’ Sims were grown under normal photoperiods (ND), short photoperiods (SD) and several night lighting regimes using red, incandescent, or far red light. Lateral branching and cutting production was promoted on P. ‘Moon Valley’ under SD while flowering was inhibited. P. ‘Moon Valley’ and P. involucrata flowered under long days. The remaining plant species produced more cuttings under ND or the night lighting treatments when compared to SD. Cycling P. ‘Moon Valley’ and P. involucrata between SD and day continuation red lighting treatments every 20 days significantly increased cutting production on plants compared to plants grown continuously under SD or ND.
Abstract
Placing lily plants in complete darkness, with or without 12 hr per day of low intensity incandescent (Inc) lighting for 5 days at 5 day intervals during the first 40 days of growth after emergence (E) had no influence on final flower bud number. Low intensity Inc lighting given as a 4 hr night interruption under natural daylight (ND) conditions for 10 days at various intervals during the first 40 days after E had no horticulturally significant influence on flower bud number. Final lily plant heights were controlled by photoperiod. Heights were reduced when plants were forced under 8 hr photoperiods (SD) when compared to ND forced plants. Heights of ‘Ace’ and ‘Nellie White’ plants were reduced by 29% and 45% when forced under SD from E to flower (F), by 19% and 42% when forced from 30 days after E to F, and by 20% and 20% when forced from visible bud to F. Repetitive light/dark cycles of 4, 6 or 12 hr had no effect on lily flower bud development rate from the time buds were 6–12 cm in length to anthesis.
Abstract
Time required to complete four developmental phases in chrysanthemum ‘Bright Golden Anne’ (Dendranthema grandiflora Tzvelev.) was determined under greenhouse conditions at constant temperature setpoints of 10, 15, 20, 25, 30, or 20 day/16C night. The four developmental phases were: I—start of short days to visible bud (2-mm-diameter terminal flower bud), II—visible bud to disbud (10-mm-diameter terminal flower bud), III—disbud to color (flower bud showing first color), and IV—color to flower. Plants either remained at the same temperature during all four phases or were moved to one other constant temperature regime after phase I, II, or III. Fastest development during all phases occurred at 20 day/16C night or constant 20C. Temperature of previous phases had less of an effect on future phases as plant development progressed. Low temperature (10C) during phase I delayed development in phase II, and high temperature (30C) during phase I and II delayed development during phase III. The length of each phase could be predicted based on the temperature preceding and during the phase. Optimum temperatures for fastest development during the four phases were calculated as 21.3, 20.3, 23.1, and 19.1C, respectively.
Tabletop Christmas tree growers whose greenhouse-grown conifers have undesirable shoot growth may alleviate this problem by applying plant growth retardants (PGRs). Some of the most common PGRs in the horticulture industry were evaluated to determine their effectiveness in controlling plant height: ancymidol at 100 μL·L-1 (ppm), daminozide at 5000 μL·L-1, paclobutrazol at 60 μL·L-1, chlormequat at 1500 μL·L-1, uniconazole at 15 μL·L-1, and ethephon at 500 μL·L-1 compared to a nontreated control. The following conifer species were used: colorado blue spruce (Picea pungens), black hills spruce (P. glauca var. densata), serbian spruce (P. omorika), noble fir (Abies procera), grand fir (A. grandis), fraser fir (A. fraseri), concolor fir (A. concolor), arborvitae (Thuja occidentalis), port orford cedar (Chamaecyparis lawsoniana), and douglas-fir (Pseudotsuga menziesii). Chlormequat was the only PGR that caused phytotoxicity and damage to the foliage was minimal. Noble fir, douglas-fir, colorado blue spruce, and arborvitae were unaffected by any PGR treatment. Daminozide reduced growth of port orford cedar and concolor fir; uniconazole reduced growth of black hills spruce and serbian spruce; paclobutrazol reduced growth of fraser fir; and ethephon reduced growth of grand fir.
Commercial production of Easter lily (Lilium longiflorum Thunb.) requires precise temperature control to ensure that the crop flowers in time for Easter sales. The objective of this project was to develop and validate a greenhouse decision-support system (DSS) for producing Easter lily to predetermined height and flower date specifications. Existing developmental models were integrated with a knowledge-based system in a DSS to provide temperature recommendations optimized for Easter lily scheduling and height control. Climate data are automatically recorded in real time by linking the DSS to a greenhouse climate control computer. Set point recommendations from the DSS can be manually set or automatically implemented in real time. Potential benefits of the project include improved crop quality and the transfer, validation, and integration of research-based models. The DSS was implemented at several research and commercial locations during the 1994 Easter lily season. DSS recommendations were compared with the strategies of experienced growers. The system design, implementation, production results, quality of recommendations, and potential are discussed.