Cut Chrysanthemum Research Articles

Temperature affects Chrysanthemum flower characteristics differently during three phases of the cultivation period

SummaryThe sensitivity to temperature of the number of flowers per plant including flower buds (NFPP), flower size, position and colour was investigated in cut chrysanthemum (Chrysanthemum morifolium cv. ‘Reagan Improved’). Plants were grown either in a glasshouse at constant 24 h mean temperatures throughout cultivation (17°C or 21°C), or in growth chambers at 32 different temperature combinations (from 15°C to 24°C). The latter temperature combinations were applied by dividing the cultivation period into three sequential phases: long-day period (phase I), start of short-day period to visible terminal flower bud (phase II), and end of phase II to harvest stage (phase III). All flower characteristics were affected significantly by temperature, except for flower position within the plant. Higher temperatures increased NFPP, mainly by increasing the number of flower buds, but decreased individual flower size. The temperature effect was also dependent on the phase of the cultivation period. In general, flower characteristics were less sensitive to temperature applied during the long-day period. NFPP was affected positively by temperature, mainly during phase III, whereas individual flower size increased with temperature during phase II, but decreased with temperature during phase III. Lower temperatures during phase III significantly enhanced flower colour intensity. Interest in using a more dynamic heating strategy is discussed.

超微小茎頂分裂組織培養法を用いたわが国のキクの新病原体キククロロティックモトルウイロイドの除去

The disease symptoms of chrysanthemum chlorotic mottle viroid (CChMVd) that had not been observed in chrysanthemum (Dendranthema grandiflorum) plants grown in Japan were found recently. In our first experimental test to examine whether the disease symptoms, such as chlorosis of newly expanded leaves in Japanese chrysanthemum, confirmed that the disease was induced by CChMVd. The viroid was detected in cultivars with the disease symptoms by polymerase chain reaction (PCR). The nucleotide sequence of CChMVd extracted from an infected ‘Piato’ plant, almost completely agreed with that of the non-symptomatic CChMVd strain that was reported previously. In the second experiment from cultivars randomly collected from various areas in Japan, namely, Fukuoka, Hiroshima, Osaka, Shiga, Kyoto and Aichi prefectures, CChMVd was detected in many of the collected cultivars. Moreover, CChMVd was detected in several samples at low concentrations from cut chrysanthemum flowers sold in Kyoto prefecture shipped from various areas in Japan and the Netherlands. Hence, we concluded that CChMVd had already spread in Japan. In the third experiment to develop a CChMVd-free plant through a newly established method, that is, leaf primordia-free shoot apical meristem (LP-free SAM) culture was utilized to eliminate CChMVd from infected cultivars. These excised LP-free SAMs derived from CChMVd-infected ‘Piato’ and ‘Sttetsuman’ plants were attached to the root tip of in vitro-sown cabbage (Brassica oleracea) ‘Harunami’ and regenerated. One out of 29 regenerated ‘Piato’ plants and two out of 6 regenerated ‘Sttetsuman’ plants were ascertained to be CChMVd-free by nested PCR.

Capillary Mats Alter the Water Content in Medium during Mist Propagation of Dendranthema

A capillary mat-mist system was developed to provide near constant media water contents at differing quantities of mist. Media water contents were reduced by increasing the capillary mat height above a constant water table maintained at bench level. Increased tensions from 0 to 10 cm above the water table reduced water content in Oasis, rockwool, and peat-perlite by 35.4%, 27.6%, and 17.4%, respectively. There was no difference in water content for each medium when the mist quantity ranged between 600 and 1800 mL·m-2·h-1, except when the capillary mat was at 9 cm above the water table and mist volume was 300 mL·m-2·h-1. Chrysanthemum cuttings rooted best when water content was highest regardless of media. Using the peat-perlite medium, water content had the greatest impact on rooting when the mist volume was low (600 mL·m-2·h-1). Relative water content of cuttings was lowest during the first 5 days of sticking and both reduced media water content and mist quantity resulted in the lowest internal water status for the cuttings.

Postharvest features of chrysanthemum cut flowers as affected by different chemicals

Cut flowers of Chrysanthemum morifolium RAM cv. Suny Reagan were treated with different concentrations of 8- hydroxyquinoline sulfate (8-HQS), silver thiosulfate (STS) and 1-methylcyclopropene (1-MCP) in order to improve the post production quality. 8-HQS was used at 200 and 400 ppm with or without sucrose at 50 O. STS was used at 0.2, and 0.4 mM with or without sucrose at 50 g/1 1-MCP was used at 0.3, 0.5 and 0.7 g/m3 for 6h.
 All the treatments of 8-HQS prolonged the vase life and minimized the percentage of weight loss of chrysanthemum cut flowers compared to the control. The vase life was larger when sucrose not combined with 8-HQS. The best treatment of 8-1-IQS was 400 ppm 8-HQS without sucrose. STS treatment led to prolong the vase life and minimized the percentage of weight loss comparing to the control. In addition, the effect was better when sucroseas was added to STS. The treatment of STS at 0.4 mM + 50 g/I sucrose was the best one. 1-MCP treatment increased the vase life and lowered the percentage of weight loss at any level comparing with untreated control. The best treatment in this concern was 1-MCP at 0.5 g/m3 for 6h. The chlorophyll content (chl.a and chl.b) of the leaves for the best treatment of each chemical was higher than that of the control. The treatment of 1-MCP at 0.5 g/m3 6h gave the best results in this respect.

Daily Temperature Integration: a Simulation Study to quantify Energy Consumption

A combined greenhouse climate and control model was used to study energy consumption in year-round cut chrysanthemum. Temperature was either controlled for energy saving with temperature integration within 24 h using the margin between heating and ventilation temperature b as control (TI) or the temperature integration regime was restricted within 24 h by a set point for negative temperature difference between average day and average night temperature T DIF to attain a temperature regime for stem length control (TI DIF). Energy consumption was reduced by both regimes compared to a standard regime according to commercial practice when heating in winter was shifted to nighttime using a screen. With increasing weather fluctuations in spring and autumn, weekly energy consumption could decrease by more than 60% for TI with ±6°C temperature bandwidth. With TI DIF in the same period, only 37 or 17% ( T DIF of −6 and −12°C, respectively) less energy was used than with a standard recommended climate regime (TP). In general, TI DIF reduced energy demand compared to TP, but energy saving was higher with TI. In deciding whether to apply either TI or TI DIF, the actual cultivation period is the most important criterion. Controlling stem length with a negative temperature difference in spring and autumn has the highest additional costs, control with almost no negative day to night temperature difference is possible in summer; during winter, both temperature control regimes result in an almost similar greenhouse climate.

Development of Planting Machine for Chrysanthemum Cuttings

Development of Planting Machine for Chrysanthemum Cuttings

Using the expolinear growth equation for modelling crop growth in year-round cut chrysanthemum.

The aim of this study was to predict crop growth of year-round cut chrysanthemum (Chrysanthemum morifolium Ramat.) based on an empirical model of potential crop growth rate as a function of daily incident photosynthetically active radiation (PAR, MJ m-2 d-1), using generalized estimated parameters of the expolinear growth equation. For development of the model, chrysanthemum crops were grown in four experiments at different plant densities (32, 48, 64 and 80 plants m-2), during different seasons (planting in January, May-June and September) and under different light regimes [natural light, shading to 66 and 43 % of natural light, and supplementary assimilation light (ASS, 40-48 micro mol m-2 s-1)]. The expolinear growth equation as a function of time (EXPOT) or as a function of incident PAR integral (EXPOPAR) effectively described periodically measured total dry mass of shoot (R2 > 0.98). However, growth parameter estimates for the fitted EXPOPAR were more suitable as they were not correlated to each other. Coefficients of EXPOPAR characterized the relative growth rate per incident PAR integral [rm,i (MJ m-2)-1] and light use efficiency (LUE, g MJ-1) at closed canopy. In all four experiments, no interaction effects between treatments on crop growth parameters were found. rm,i and LUE were not different between ASS and natural light treatments, but were increased significantly when light levels were reduced by shading in the summer experiments. There was no consistent effect of plant density on growth parameters. rm,i and LUE showed hyperbolic relationships to average daily incident PAR averaged over 10-d periods after planting (rm,i) or before final harvest (LUE). Based on those relationships, maximum relative growth rate (rm, g g-1 d-1) and maximum crop growth rate (cm, g m-2 d-1) were described successfully by rectangular hyperbolic relationships to daily incident PAR. In model validation, total dry mass of shoot (Wshoot, g m-2) simulated over time was in good agreement with measured ones in three independent experiments, using daily incident PAR and leaf area index as inputs. Based on these results, it is concluded that the expolinear growth equation is a useful tool for quantifying cut chrysanthemum growth parameters and comparing growth parameter values between different treatments, especially when light is the growth-limiting factor. Under controlled environmental conditions the regression model worked satisfactorily, hence the model may be applied as a simple tool for understanding crop growth behaviour under seasonal variation in daily light integral, and for planning cropping systems of year-round cut chrysanthemum. However, further research on leaf area development in cut chrysanthemum is required to advance chrysanthemum crop growth prediction.

Process-based humidity control regime for greenhouse crops

Modern greenhouses in The Netherlands are designed for efficient use of energy. Climate control traditionally aims at optimal crop performance. However, energy saving is a major issue for the development of new temperature regimes. Temperature integration (TI) results in fluctuating and often high relative humidity (RH) levels in modern, highly insulated greenhouses. At high temperature, water vapour pressure deficit (VPD) is usually high and RH consequently low and vice versa. Relatively low fixed set points (80–85% RH) for air humidity as is common practice, may strongly influence the efficiency of TI, because heating and/or ventilation actions are required to control humidity rather than temperature. This requires much energy. Fluctuating RH may affect crop performance in several ways. Too low VPD may reduce growth due to low transpiration and associated physiological disorders. Water vapour pressure above the dew point leads to condensation on the relative cooler plant tissue and this may give rise to diseases. High VPD, on the other hand, may induce high stomatal resistance and plant water stress (PWS). The aim of the present research was the design of a process-based humidity control concept for a reference cut chrysanthemum crop cultivated with TI. RH control set points were generated as function of underlying processes. Greenhouse performance with this humidity regime and different temperature regimes were simulated with respect to greenhouse climate, energy consumption and photosynthesis. Compared with a fixed 80% RH set point, annual energy consumption of a year-round cut chrysanthemum cultivation could be reduced by 18% for TI with ±2 °C temperature bandwidth as well as for regular temperature control. For separate 12 week cultivations with planting date 1 March, energy saving could increase up to 27 or 23% for TI and regular temperature control, respectively.

Ácido giberélico (GA3) no crisântemo (Dedranthema grandiflora Tzvelev.) de corte 'viking': cultivo verão/outono

Este trabalho tem como objetivo avaliar a ação do ácido giberélico (AG3) em plantas crisântemo de corte 'Viking' quanto a parâmetros fenométricos, melhor época e concentração da aplicação para obter-se hastes de melhor qualidade no cultivo de verão/outono. Avaliou-se o efeito de cinco épocas de aplicação (sem aplicação, aplicação na segunda, quarta, oitava e décima semana após o plantio) e quatro concentrações (0, 100, 200 e 300 mg.L-1 de GA3). Verificou-se que as maiores alturas foram obtidas com as aplicações na segunda e quarta semanas de cultivo e nas concentrações entre 200 a 300 mg.L-1. O maior diâmetro de haste e pedúnculo floral foram obtidos com a aplicação de 100 a 200 mg.L-1 GA3 na quarta semana. A concentração de 200 mg.L-1 de GA3, independente da época de aplicação proporcionou a antecipação do florescimento em cinco dias, todas as concentrações aplicadas a partir da oitava semana provocaram o clareamento do disco floral.

Effect of the different timing of AMF inoculation on plant growth and flower quality of chrysanthemum

Plant growth and flower quality of an ornamental plant ( Chrysanthemum morifolium Ramat) var. Baekgwang in response to the different timing of arbuscular mycorrhizal fungi (AMF) inoculation were examined. To evaluate the effects of AMF inoculation timing on growth of chrysanthemum cuttings, AMF was directly inoculated to cutting (AMFD), or inoculated at transplanting stage (AMFA). Control plants did not receive AMF inoculation (CON). A significant difference in plant growth was observed in AMF treatment compared to non-inoculated treatment at transplanting stage. Rooting rate in AMF treatment was 99% whereas it was 76% in non-mycorrhizal inoculation. The colonization rate was 3.9% in AMF treatment, while it was 0% in non-AMF treatment. Tap root length and number of lateral roots in AMF treatment were twice than those of non-AMF treatment. Inoculation of AMF significantly increased shoot and root growth at transplanting stage. At 7 weeks after transplanting, chrysanthemum plants in AMFD and AMFA treatments had 46.42 and 34.24% colonization rate, respectively. Low colonization rate (6.08%) was observed in CON, possibly due to contamination. Plant height, leaf area, root length, and fresh and dry weight of shoots, stems and roots in AMF inoculation treatments (AMFD and AMFA) were significantly higher than control plants. AMF inoculation significantly shortened flowering time compared to non-AMF plants. Chrysanthemum in AMFD, AMFA and CON treatments flowered at 98, 104 and 112 days after transplanting, respectively. Fresh weight, width and height of flowers in AMFD and AMFA treatments were generally higher than those in CON. However, a significant increase in fresh weight, width and height of flowers was found in AMFD treatment. A significant increase of macronutrient uptake in leaves was observed for AMFD treatment, compared with CON. Mn uptake in AMFD and AMFA was more than double than that in CON. In roots, macro and micronutrient concentrations were generally higher in AMFD.

Ethylene-induced Leaf Yellowing in Cut Chrysanthemums (Dendranthema grandiflora Kitamura)

Twelve cultivars of cut flowering chrysanthemums (Dendranthema grandiflora Kitamura) were exposed continuously to air with or without 1 ppm ethylene and their leaf color was measured with a chromameter. When leaves of six cultivars, including 'Syuho-no-chikara' and 'Seiko-no-makoto', were exposed to ethylene, they turned yellow, but others did not respond to ethylene. Similar varietal sensitivity to ethylene and consequent leaf yellowing were observed in resetted and elongating vegetative shoots. Pulsing with 0.2 mM anionic silver thiosulfate complex (STS) completely inhibited leaf yellowing in the ethylene-containing atmosphere. These results indicate that yellowing of the leaves of some chrysanthemum cultivars is induced by ethylene.

Temperature integration and DIF in cut chrysanthemum

SummaryTo reduce energy consumption in greenhouses, temperature integration can be used. However, the temperature integration principle considers only average temperatures and does not comply with the DIF concept (DIFference between mean day temperature and mean night temperature). With DIF, stem elongation, one of the major quality aspects of many crops, can be controlled. Short compact plants can be achieved by a negative DIF (average night temperature > average day temperature). In spring, summer and autumn temperature integration usually results in positive DIF and therefore longer stems. The aim of this study was to investigate whether temperature integration and DIF could be applied simultaneously. Greenhouse temperature fluctuates with temperature integration. During spring or autumn it is difficult to obtain short compact plants by a negative DIF with regular temperature integration. In this research, temperature integration was therefore modified by applying two independent integration regimes, one for daytime and one for nighttime while a zero DIF was set. Simulations and experiments with standard temperature control, regular and modified temperature integration showed that temperature integration and DIF could be applied simultaneously, while energy consumption and stem elongation were reduced.

Morphological Observation on Viable and Nonviable Axillary Bud Formation in Non-branching Chrysanthemum 'Iwanohakusen'

Young, non- induced to flowering cuttings of the non-branching chrysanthemum [Dendranthema × grandiflorum (Ramat.) Kitamura) 'Iwanohakusen' were exposed to 30/20°C (day/night) to test whether the treatment inhibited differentiation of axillary buds from the shoot meristem. For comparison, comparable cuttings were grown at 20/15°C (control). Axillary bud initiation on plants, grown at 30/20°C, occurred, and the initials developed to a shell zone and a small mound of meristematic tissue in the leaf axils. However, they did not progress to the prophyll and leaf primordial stages as did the axillary buds of the control plants. Thus, the elevated temperature treatment did not affect the initiation of axillary buds, but it inhibited the meristem to differentiate further. Therefore, we consider that exposure to high temperature prevents differentiation of the prophyll and leaf primordium.

Effect of assimilate availability on flower characteristics and plant height of cut chrysanthemum: an integrated study

SummaryThe influence of assimilate availability on the number of flowers per plant, individual flower size and plant height of chrysanthemum was investigated in different seasons, integrating the results from eight greenhouse experiments. Increased assimilate availability was obtained by higher light intensity, higher CO2 concentration, lower plant density or longer duration of the long-day (LD) period. Within each experiment, conditions that were expected to increase assimilate availability indeed resulted in higher total dry mass of the plant, excluding roots (TDMp). In contrast, flower mass ratio was hardly affected, except for the increased duration of the LD period that signi®cantly reduced the partitioning towards the flowers. Consequently, an increase in total flower dry mass with assimilate availability was observed and this was mainly a result of higher numbers of flowers per plant, including flower buds (NoF). Individual flower size was only influenced by assimilate availability when average daily incident PAR during short-day period was lower than 7.5 mol m–2 d–1, resulting in lighter and smaller flowers. Excluding the positive linear effect of the duration of the LD period, assimilate availability hardly influenced plant height (<10% increase). It is concluded that within a wide range of growth conditions chrysanthemum invests additional assimilates, diverted to the generative organs, in increasing NoF rather than in increasing flower size. Irrespective of the growth conditions and season a positive linear relationship (r2 = 0.90) between NoF and TDMp was observed. This relationship was cultivar-specific. The generic nature of the results is discussed.

Simulation of leaf area development based on dry matter partitioning and specific leaf area for cut chrysanthemum.

This work aims to predict time courses of leaf area index (LAI) based on dry matter partitioning into the leaves and on specific leaf area of newly formed leaf biomass (SLA(n)) for year-round cut chrysanthemum crops. In five glasshouse experiments, each consisting of several plant densities and planted throughout the year, periodic destructive measurements were conducted to develop empirical models for partitioning and for SLA(n). Dry matter partitioning into leaves, calculated as incremental leaf dry mass divided by incremental shoot dry mass between two destructive harvests, could be described accurately (R(2 )= 0.93) by a Gompertz function of relative time, R(t). R(t) is 0 at planting date, 1 at the start of short-days, and 2 at final harvest. SLA(n), calculated as the slope of a linear regression between periodic measurements of leaf dry mass (LDM) and LAI, showed a significant linear increase with the inverse of the daily incident photosynthetically active radiation (incident PAR, MJ m(-2 )d(-1)), averaged over the whole growing period, the average glasshouse temperature and plant density (R(2 )= 0.74). The models were validated by two independent experiments and with data from three commercial growers, each with four planting dates. Measured shoot dry mass increase, initial LAI and LDM, plant density, daily temperature and incident PAR were input into the model. Dynamics of LDM and LAI were predicted accurately by the model, although in the last part of the cultivation LAI was often overestimated. The slope of the linear regression of simulated against measured LDM varied between 0.95 and 1.09. For LAI this slope varied between 1.01 and 1.12. The models presented in this study are important for the development of a photosynthesis-driven crop growth model for cut chrysanthemum crops.

EFFECT OF LIGHT INTENSITY, PLANT DENSITY, AND FLOWER BUD REMOVAL ON THE FLOWER SIZE AND NUMBER IN CUT CHRYSANTHEMUM

Flower size and number of flowers per plant are important external quality aspects in cut chrysanthemum. The present work is conducted in a glasshouse and aims at investigating how these quality aspects can be predicted. To evaluate individual flower size, different levels of supplementary lighting (control and assimilation light), plant density (32, 48 and 64 plants m-2) and lateral flower bud removal (leaving 1 flower, 4 flowers and control) were applied. To analyse the effect of assimilate supply on number of flowers per plant, three light intensities (no shade control, 65␕ight, and 45␕ight) where combined with three plant densities (32, 64, and 80 plants m-2). Individual flower size was negatively influenced by competition for assimilates in the treatments with a fixed number of flowers per plant (1 or 4 flowers). In such treatments, plants grown under no supplementary assimilation light, higher plant density, or with higher number of flowers per plant resulted in significantly lower individual flower dry mass and area. However, when no lateral flower buds were removed (control), higher assimilate supply resulted in more flowers rather than in larger flowers. Number of flowers per plant (including flower buds) showed a positive linear increase with total dry mass per plant. The combination of 32 plants m-2 and no shade resulted in the highest number of flowers per plant (33 flowers) in contrast with 80 plants m-2 and 45␕ight intensity (only 9 flowers).

A SIMULATION STUDY ON THE INTERACTIVE EFFECTS OF RADIATION AND PLANT DENSITY ON GROWTH OF CUT CHRYSANTHEMUM

In the present study, we used a photosynthesis-driven crop growth model to determine acceptable plant densities for cut chrysanthemum throughout the year at different intensities of supplementary light. Dry matter partitioning between leaves, stems, and flowers was simulated as a function of crop developmental stage. Leaf area index was simulated as leaf dry mass multiplied by specific leaf area, the latter being a function of season. Climatic data (hourly global radiation, greenhouse temperature, and CO2 concentration) and initial organ dry mass were model inputs. Assimilation lights were switched on and off based on time and ambient global radiation intensity. Simulated plant fresh mass with supplementary light (49 µmol m-2 s-1) for 52 cultivations (weekly plantings, reference plant densities, and length of the long and short day period) was used as reference plant fresh mass. For four other supplementary light intensities (31, 67, 85, and 104 µmol m-2 s-1), dry matter production was simulated with the reference plant density and length of the long and short day period for each planting week and plant fresh mass was calculated. The acceptable plant density was then calculated as the ratio between plant fresh mass and reference plant fresh mass multiplied by the reference density. Under low natural light intensities, plant density could be increased substantially (>30%) at increased supplementary light intensities, while maintaining the desired plant mass. Simulated light use efficiency (g additional dry mass ? MJ-1 additional supplementary light) was higher in winter (4.7) than in summer (3.5), whereas it hardly differed between the supplementary light intensities. This type of simulations can be used to support decisions on the acceptable level of plant density at different intensities of supplementary lighting or lighting strategies and on optimum supplementary light intensities.

Effect of day and night temperature on internode and stem length in chrysanthemum: is everything explained by DIF?

In many plant species, including chrysanthemum, a strong positive correlation between internode length and DIF [difference between day (DT) and night (NT) temperature] has been observed. However, Langton and Cockshull (1997. Scientia Horticulturae 69: 229-237) reported no such relationship and showed that absolute DT and NT explained internode length rather than DIF. To investigate these conflicting results and to clarify the validity of the DIF concept, cut chrysanthemums (Chrysanthemum 'Reagan Improved') were grown in growth chambers at all 16 combinations of four DT and four NT (16, 20, 24 and 28 degrees C) with a 12 h day length. Length of internode 10, number of internodes and stem length were measured on days 5, 10, 17, 22 and 27 after starting the temperature treatments. Internode length on day 10 showed a positive linear relationship with DIF (R2 = 0.64). However, when internodes had reached their final length in all treatments (day 27), a much stronger positive linear relation was observed (R2 = 0.81). A model to predict final internode length was developed based on the absolute DT and NT responses: both responses were optimum curves and no significant interaction between DT and NT occurred [final internode length (mm) = -32.23 + 3.56DT + 1.08NT - 0.0687DT2 - 0.0371NT2; R2 = 0.91, where TD is day temperature and TN is night temperature]. It is shown that DIF can predict final internode length only within a temperature range where effects of DT and NT are equal in magnitude and opposite in sign (18-24 degrees C). Internode appearance rate, as well as stem length formed during the experiment, showed an optimum response to DT.

Wounding-induced xylem occlusion in stems of cut chrysanthemum flowers: roles of peroxidase and cathechol oxidase

A wounding-induced xylem occlusion, resulting in severe leaf wilting, occurs in stems of cut chrysanthemum flowers (Dendranthema grandiflora), cv. Vyking. The blockage develops after about 1 h in flowers held in air at 20 °C. It is initially located in the lowermost 2 cm of the stem and upon prolonged exposure to air it is also found above 2 cm. We tested the possible role of peroxidase (EC 1.11.1.7) and phenoloxidases in the blockage. Some peroxidase inhibitors (copper ions and 3-amino-1,2,4-triazole) delayed the occlusion, and treatment with compounds that inhibit peroxidase but stimulate phenoloxidase (catechol, hydroquinone, p-phenylene diamine) had the same effect. Some inhibitors of phenoloxidase (p-nitrophenol, p-chlorophenol, p-nitrocatechol, and sodium metabisulfite) also delayed the occlusion. Phenoloxidase activity in plants comprises catechol oxidase (EC 1.10.3.1) and laccase (EC 1.10.3.2). The blockage was considerably delayed by catechol oxidase inhibitors (tropolone and 4-hexylresorcinol), even more so than with general phenoloxidase inhibitors. The results indicate that the occlusion is mainly due to a physiological (oxidative) process, requiring both peroxidase and catechol oxidase activity.

LIGHT ON CUT CHRYSANTHEMUM: MEASUREMENT AND SIMULATION OF CROP GROWTH AND YIELD

The effects of plant density and light intensity on crop growth and yield of cut chrysanthemum were investigated experimentally and simulated with a generic explanatory crop growth model (HORTISIM). In winter, supplementary light (HPS; 48 μmol m-2 s-1 PAR) increased total incident PAR with 24°whereas total dry matter production per m2 was increased with 45EThe effect of supplementary light on plant dry and fresh mass, and number of flowers per plant at different plant densities (32, 48 or 64 m-2), was larger at lower densities. In summer, a linear relationship between cumulative dry mass production and cumulative intercepted PAR was observed in each of three shading treatments. However, the slope of this line (light use efficiency) decreased with increasing light level being 4.1 g MJ-1, 3.4 g MJ-1 and 2.7 g MJ-1 for 43°66 nd 100␕ight, respectively. HORTISIM could accurately predict crop growth and yield at most light conditions, with measured climatic data, initial plant mass and time course of leaf area index being model inputs. However, in summer at 100␕ight the model strongly overestimated dry mass production.