Royal D. Heins

Stem elongation and flowering of the long-day plant Campanula isophylla Moretti in response to day and night temperature alternations and light quality

Abstract Stem elongation and plant height at flowering in Campanula isophylla Moretti were greater when plants were exposed to far red (FR) light or light from incandescent lamps which had a low red (R)/FR ratio (0.7). The difference in final stem length between FR- and R-light-treated plants was greatest when the light treatments were given during the entire night or as a 3 h end-of-day (EOD) lighting period. Only minor differences existed between R and FR light treatments when plants were given light in the middle of the night. However, FR light suppressed lateral branching compared with R light. The reduction in plant height as a result of a lower day temperature (DT) than night temperature (NT) was nullified by day-extension lighting with incandescent lamps. With fluorescent lamps (R/FR ratio 4.2), plant heightwas significantly less at 15/21°C (negative DT-NT (DIF)) than at 21/15°C DT/NT (positive DIF). Continuous lighting (CL) during the entire night or with 3 h night interrupttion (NI) treatments with R or FR light immediately after the middle of the night was equally effective at inducing flowering, and much more effective than EOD or end-of-night (EON) lighting. DIF had a slight influence on the rate of flower development, but negative DIF grown plants had 24% more flowers and flower buds, and 26% higher dry weight, than positive DIF plants. Practical applications of light quality and negative DIF treatments for the production of high-quality pot plants of C. isophylla are discussed.

Irradiance and temperature effects on time of development and flower size in chrysanthemum

Abstract The effects of day temperature (DT), night temperature (NT) and photosynthetic photon flux (PPF), on rate of development and flower size were studied in chrysanthemum ( Dendranthema grandiflora Tzvelev. cultivar ‘Bright Golden Anne’). DT and NT ranged from 10 to 30°C and PPF from 1.8 to 21.6 mol day −1 m −2 . Flower initiation did not occur after 100 short days (SD) at low PPF levels (1.8 mol day −1 m −2 ) in combination with high DT or NT (30°C). The number of days to flower varied from 58 to 140 days among plants grown under environmental conditions allowing flower initiation within 100 SD. The time to flower from start of SD decreased nonlinearly as PPF increased. Increasing PPF by 9.9 mol day −1 m −2 at 20°C accelerated flowering 20 days when the initial PPF was 1.8 mol day −1 m −2 , but only 10 days when the initial PPF was 11.7 mol day −1 m −2 . The DT and NT for most rapid flower development were estimated from a model predicting time to flower. Independent of PPF in the range from 2 to 20 mol day −1 m −2 , the optimum DT was 17°C and the optimum NT was 18°C. Total flower area per plant varied from 14 to 310 cm 2 . The flower size increased linearly as PPF increased from 1.8 to 21.6 mol day −1 m −2 at a constant temperature of 20°C. The optimum DT NT combination for largest flower size changed from 21 14° to 20 18° C as PPF increased from 5 to 20 mol day −1 m −2 .

Influence of ethanol on ethylene biosynthesis and flower senescence of cut carnation

Abstract Ethanol in the holding-solution inhibited climacteric ethylene (C 2 H 4 ) biosynthesis and decreased the respiration rate 60% during a 7-day period in cut carnation flowers. Conversion of 1-aminocyclopropane-1-carboxylic acid (ACC) to C 2 H 4 was inhibited by adding ethanol to the holding-solution. Simultaneously, ACC-induced senescence in carnation flowers was inhibited by ethanol. Ethanol was the most effective alcohol in delaying carnation flower senescence of the tested series methanol, ethanol, propanol, tert-butanol and n-butanol. Ovary development was also inhibited in carnation flowers by ethanol. The senescence of Easter lily flowers ( Lilium longiflorum ) and tulip flowers ( Tulipa gesneriana ) was not delayed by ethanol.

Computer-Vision-Based System for Plant Growth Analysis

A computer vision system with a CCD camera and an infrared lighting apparatus was developed to conduct noncontact, three-dimensional plant growth analyses. The infrared lighting apparatus was designed to obtain plant images in the dark by exposing plants to wavelengths of 800 nm and greater. Processing algorithms were developed to extract plant outlines, detect node positions, and produce thinned lines from images. The system was capable of resolving interimage differences of 5% of a pixel, or 0.025 mm.

Temperature driven leaf unfolding rate in Hibiscus rosa-sinensis

Leaf unfolding rate of Hibiscus rosa-sinensis cultivars ‘Brilliant Red’ and ‘Pink Versicolor’ was determined in the 5–35°C temperature range at intervals of 6°C. Plants of neither cultivar survived at 5°C, and growth was very slow at 11°C. The rate of leaf unfolding was similar for the two cultivars in the studied temperature range. Daily leaf unfolding rate for hibiscus was described by a cubic polynomial function of temperature (T) where leaves day−1 = 0.06289 − 0.02026 · T + 0.001750 · T2 − 0.00002983 · T3. Based on this function, predicted leaf unfolding varied from 0.012 leaves day−1 at 11°C to a maximum of 0.229 leaves day−1 at 32°C. A linear function (leaves day−1 = − 0.1130 + 0.01148·T) approximated the curvilinear relationship in the range from 10–30°C. A degree-day relationship was calculated to 0.0115 leaves per degree day using the linear function with a base temperature of 9.8°C. To unfold one leaf, 87 degree-days were required as determined by the developed linear model. A linear model was developed from the linear function where leaf unfolding was 0 at temperatures < 10°C and leaf unfolding was calculated at 30°C at temperatures ≥ 30°C. The cubic function and the linear model predicted a similar leaf unfolding rate based on hourly average temperatures recorded in a Florida commercial greenhouse during two times of the year. During a 78-day period from 25 February to 14 May, 9.95 and 9.98 leaves were predicted to unfold by the linear and cubic models respectively. During a 65-day period from 21 July to 24 September, 12.28 and 12.04 leaves were predicted to unfold by the linear and cubic models respectively. The predicted leaf unfolding rate was compared with actual leaf unfolding for the nine cultivars ‘Aloha Pink’, ‘Brilliant Red’, ‘Euterpe’, ‘Florida Sunset’, ‘Painted Lady’, ‘Pink Versicolor’, ‘Sundance’, ‘Tawny’, and ‘Vista’. Predicted leaf unfolding was within 0.9 leaves of observed leaf unfolding for all cultivars over a 7-week period after pinching. After about 7 weeks, the models progressively overpredicted leaf unfolding. Over-prediction was correlated with the appearance of flower buds.

LOW-TEMPERATURE STORAGE OF BEDDING-PLANT PLUGS

Ageratum, begonia, marigold, and salvia seedlings growing in individual cells were stored to determine the effects of temperature, irradiance, and storage time on growth and forcing time after transplanting. Photosynthetic photon flux densities of 0, 1, and 5 μmol·m−2·s−1 were combined with temperatures of 0.0, 2.5, 5.0, 7.5, 10.0, and 12.5C to create 18 unique storage environments. Sample plants were removed at 1-week intervals for a period of at least 6 weeks, and were forced into flower. In all four species, chilling injury increased as storage at 0.0 and 2.5C was extended, and surviving plants flowered late relative to controls. Ageratum was most sensitive to chilling injury, followed in order by salvia, marigold, and begonia. Plant deterioration and ultimately death occurred as dark storage duration increased at 10 and 12.5C. Greatest percent survival and highest quality of seedlings stored in the dark occurred at temperatures just above those that caused chilling injury. Exposure to 1 μmol·m−2·s−1 during storage greatly increased quality of plants held at warmer-than-optimal temperatures. No substantial differences were observed among plants stored with 1 versus 5 μmol·m−2·s−1. All four species could be stored for 6 weeks in the light, but their responses to storage temperatures and durations differed. Optimal temperatures were 5–7.5C for begonia, 5C for marigold, and 7.5C for salvia and ageratum.

A decision-support system for real-time management of Easter lily (Lilium longiflorum Thunb.) scheduling and height—I. System description

Abstract A decision-support system was developed for recommending night and day temperature settings to control the timing and height of Easter lily ( Lilium longiflorum Thunb.). Existing biological models and qualitative rules were combined into an overall model of the response of plant development rate to temperature. A process control algorithm was used to determine appropriate height control actions based on a graphical control chart of plant height over time. A knowledge-based system checked the feasibility of output from the development and height control models and generated a text report. This model was implemented on a personal computer in a program called “The Greenhouse CARE System” and has been linked directly with an environmental computer to control greenhouse temperatures. A companion article describes validation of this model.

A decision-support system for real-time management of Easter lily (Lilium longiflorum Thunb.) scheduling and height--II. Validation

Abstract Computer decision-support systems (DSS) are interactive programs that provide model recommendations in a problem area. An experiment was conducted to validate a DSS for scheduling and height control of Easter lily ( Lilium longiflorum Thunb.) called The Greenhouse CARE System . The DSS was used to recommend temperature settings in three locations (Michigan, California and Denmark) with the goal of producing Easter lilies to predefined flowering and visible bud dates, and to plant height targets. Day and night temperature settings recommended by the DSS were the sole method used to control timing and, secondarily, plant height. Flowering of 50% of plants occurred on the specific target date in two locations and was one day early in the third location. The DSS was less able to achieve a target visible bud date, and information from commercial crops grown with the DSS indicated changes needed to implement a leaf unfolding rate model. Plant height was consistently taller than desired, indicating that growth retardants need to be included in future model recommendations. DSS temperature recommendations were similar to those made by experienced Easter lily producers.

The influence of diurnal temperatures on the postharvest susceptibility of poinsettia to Botrytis cinerea

The influence of day/night (DT/NT) temperatures of 16/16, 19/19, 22/22, 16/19, 19/22, 16/22, 19/16, 22/19, and 22/16°C during poinsettia production on postharvest bract and foliage susceptibility to Botrytis cinerea was investigated. Plants were inoculated with 2.7 x 10 5 B. cinerea conidia per ml of water following a 3- or 6-week temperature treatment and incubated at 20°C. Area under the disease progress curve (AUDPC) data indicated that the postharvest susceptibility of poinsettia bracts and foliage to B. cinerea, measured by the proportion of bracts and foliage infected and the proportion with sporulating B. cinerea, was not influenced by the difference in DT and NT but increased as DT or NT during production increased. As plants matured, as indicated by thermal time, AUDPC values increased (P = 0.001) more for the proportion of bracts infected (R 2 = 0.73) than for the proportion of bracts with sporulating B. cinerea (R 2 = 0.86) and the proportion of foliage with sporulating B. cinerea (R 2 = 0.74). Results suggested that commercial growers using higher NT than DT to limit poinsettia height are not increasing the postharvest susceptibility of their crop to B. cinerea. However, the increased susceptibility of maturing poinsettias suggests disease management strategies should be intensified during crop finishing and Dostharvest handling.

Controlled Flowering of Herbaceous Perennial Plants

We have determined the juvenility, cold (vernalization), photoperiod, and cultural requirements necessary to flower many herbaceous perennials on specific dates and at specified sizes. We identified the long-day (LD) requirement by conducting critical photoperiod experiments in which critical photoperiod is defined as the photoperiod that elicits a complete, rapid, uniform flowering response in a population. The LD requirement for all herbaceous perennials tested can be met by either a continual photoperiod of 16 hours or more, or by four hours of light as an interruption in the middle of the night. Nightinterruption lighting for two hours is adequate for rapid, uniform flowering in some species. Incandescent, cool-white fluorescent, metal halide, and high-pressure sodium lamps effectively promote an LD response; differences among the irradiance levels required for flower induction are horticulturally insignificant. To maintain vegetative growth on quantitative and qualitative LD species, photoperiods should be 10 hours or fewer.