Moving lamps increase leaf photosynthetic capacity but not the growth of potted gerbera

To investigate the responses of leaf photosynthesis and plant growth to a moving lighting system, potted gerberas (Gerbera jamesonii H. Bolus ex J.D. Hook “Festival”) were grown under supplemental lighting in a greenhouse with either a stationary or a moving lighting system positioned above the benches. The stationary system consisted of a fixed high pressure sodium (HPS) lighting system, while the moving lighting system consisted of a moving HPS fixture attached to a cable system to move the light fixture back and forth over the crop. In both cases, the supplemental lighting was applied from 6:00 to 24:00 h with the same supplemental daily light integral (4.9 mol m⁻² day⁻¹). Moving lamps significantly increased leaf photosynthetic capacity as represented by light saturated net CO₂ exchange rate (NCER) (A_sat), light- and CO₂-saturated rate of NCER (A_max), maximum rate of Rubisco carboxylation (V_cmax), maximum rate of electron transport (J_max) and rate of triose phosphate utilization. However, in situ leaf NCER and stomatal conductance, leaf chlorophyll content index, leaf area, leaf thickness, fresh weight of plants were significantly lower under moving lighting than under stationary lighting. It is suggested that the reduced growth of plants under moving lighting might be due to (1) the overall lower light use efficiency of leaves under moving lighting than those under stationary lighting; (2) the slower response time of the photosynthetic system compared to the rate of change in light intensity under moving lighting.     

Effects of intracanopy lighting on photosynthetic characteristics in cucumber

Plants of cucumber (Cucumis sativus L. cv. Euphorbia) were grown in a traditional high-wire cultivation system to investigate the effects of three lighting regimes on photosynthetic characteristics, leaf area and yield. The lighting regimes included overhead lighting (OH), where all the lamps were mounted above the canopy and overhead + intracanopy lighting (OH + IC) which comprised 65% of overhead lamps and 35% of lamps mounted vertically along the plant rows. All overhead lighting was provided for 20 h day⁻¹ and intracanopy lighting was provided for either 20 h or 24 h day⁻¹ lighting period. Intracanopy lighting improved the light distribution in the canopy. Gas exchange measurements showed that intracanopy lighting increased net photosynthesis (P_N) and photosynthetic capacity (P_max). Parameters calculated from CO₂ response (A/C_i) curves showed that in vivo estimate of the maximum rate of Rubisco carboxylation (Vc_max) and the maximum rate of electron transport (J_max) were affected by light regime. Intracanopy light increased yield by 11% compared to traditional overhead light.     

Effects of interlighting on yield and external fruit quality in year-round cultivated cucumber

The effects of interlighting and of the proportion of interlight on the yield and fruit quality of year-round cultivated cucumber (Cucumis sativus L. cv. Cumuli) were investigated for this study. Artificial lighting was provided by high pressure sodium (HPS) lamps and the lighting regimes included top lighting (TL), top + interlighting 24% (T + IL24) and top + interlighting 48% (T + IL48). In TL, all of the lamps were mounted above the canopy. In T + IL24 and T + IL48, top lamps covered 76 and 52% of the lighting, respectively, while 24 and 48% of the lighting came from interlighting lamps which were mounted vertically 1.3 m above the ground between the single plant rows. The outdoor daily light integral (DLI) varied greatly during the cultivation periods; the mean values were 36.8, 5.3 and 19.9 mol m⁻² day⁻¹ for the summer, autumn–winter and spring stands, respectively. Lighting regime affected both yield and external fruit quality. Interlighting increased first class yield and decreased unmarketable yield, both in weight and number. The increase in the annual first class yield in weight was 15% in the two T + IL regimes. Interlighting improved energy use efficiency in lighting, being for the whole year 120, 130 and 127 g total yield kW h⁻¹ in TL, T + IL24 and T + IL48, respectively. Interlighting increased the fruit skin chlorophyll concentration in all seasons, but had only a minor effect on the fruit dry matter concentration. The mean total chlorophyll concentration in fruit skin was 70.8, 76.7 and 82.2 μg cm⁻² in TL, T + IL24 and T + IL48, respectively. In addition, interlighting extended the post-harvest shelf life of cucumber fruits in spring. Besides interlighting per se, also the higher proportion of interlight tended to further improve the fruit quality. For example, the fruit skin chlorophyll concentration increased along with the higher proportion of interlighting. In general, the effects of lighting regime were more prominent in lower natural light conditions in winter and spring. It is concluded that interlighting is a recommendable lighting method in cucumber cultivation, especially in lower natural light conditions.     

Analysis and modeling of gas exchange processes in Scaevola aemula

Scaevola aemula is a popular ornamental crop cultivated as a bedding plant or for hanging baskets. We characterized gas exchange properties of S. aemula ‘New Wonder’ in response to photosynthetically active radiation (PAR), carbon dioxide concentration, and leaf temperature. Net CO₂ assimilation rate (A) was responsive to CO₂, exhibiting a saturation when intercellular CO₂ concentration (C_i) was greater than 600 μmol mol⁻¹. Net CO₂ assimilation rate and dark respiration rate (R_d) were 23.1 and 2.3 μmol m⁻² s⁻¹, respectively, at 25 °C and PAR = 1500 μmol m⁻² s⁻¹. Net CO₂ assimilation rates were similar at leaf temperatures between 20 and 30 °C but significantly reduced at 15 °C. These gas exchange results were used to test the extendibility of a coupled gas exchange model previously developed for cut-roses. Utilizing the gas exchange data measured at 25 °C leaf temperature, several model parameters were independently determined for S. aemula. Model predictions were then compared with observations at different leaf temperatures. The model predicted the rates of net CO₂ assimilation and transpiration of S. aemula reasonably well. Without additional calibration, the model was capable of predicting the temperature dependence of net CO₂ assimilation and transpiration rates. Applying the model to predict the effects of supplemental lighting and CO₂ enrichment on canopy photosynthesis and transpiration rates, we show that this model could be a useful tool for examining environmental control options for S. aemula production in the greenhouse.     

Cost-efficient light control for production of two campanula species

A cost-efficient light control system based on weather forecasts, electricity prices and daily photosynthesis integral (DPI) was evaluated for application in the commercial production of the long-day (LD) plant Campanula portenschlagiana ‘Blue Get Mee’ and C. cochlearifolia ‘Blue Wonder’. Experiments were conducted under both autumn and spring conditions and included four treatments. Three treatments were controlled by the software system DynaLight Desktop which automatically defined the most cost-efficient use of supplemental light, -based on a predefined set point of DPI, forecasted solar irradiance and the market price on electricity. The set points of DPI in the three treatments were 300, 450 and 600 mmol CO₂ m⁻² leaf d⁻¹ and the treatments were compared with a traditional LD 19-h treatment. The DPI-based light control strategy resulted in very irregular light patterns including daily periods of solar irradiance combined with supplemental light in low light periods and a night period interrupted by irregular light breaks (NB-lighting). Both campanula species flowered in the DPI-based treatments during spring, but the flowering percentage was low and non-uniform during autumn. This was caused by a combination of the irregular light, low natural light intensities and a decrease in daily light integral (DLI), and could be restored by maintaining a continuous 19 h photoperiod with incandescent lamps (<5 μmol m⁻² s⁻¹), illustrating that photoperiod was an important factor for flowering in LD species grown under low light intensities. Growth in terms of carbon gain was marginally affected by the irregular light and a 25% reduction in electricity costs was achieved without major reductions in plant quality in spring. Our results illustrate that plant production of LD species can be maintained in a cost-efficient light control system where the use of supplemental light is based on weather forecasts and electricity prices.     

An upper limit for elevated root zone dissolved oxygen concentration for tomato

It is well understood that insufficient oxygen within plant root zones can greatly diminish plant productivity. However, little is known about the effect of elevated root zone oxygen concentrations. Tomato (Lycopersicon lycopersicum Mill., cv. Trust) seedlings were grown in nutrient solutions containing dissolved oxygen (DO) concentration ranging from 5.3 to 40 mg L⁻¹ for 4 weeks. There were no visible symptoms observed on the leaves or stems in any of the treatments. Leaf chlorophyll content was higher in the 40 mg L⁻¹ treatment than with 20 and 30 mg L⁻¹ DO treatments. Two weeks from the start of the experiment, roots in the 40 mg L⁻¹ treatment exhibited stunted growth, became thicker, and had fewer side and fine roots compared to roots in the lower levels of DO treatment. Almost all the measured growth parameters (fresh and dry weights of root, stem, and leaf, leaf area, stem diameter) were significantly reduced in plants grown in the 40 mg L⁻¹ treatment compared to plants in the lower level of DO treatments, except that the plant height increased with the increasing DO concentration. Root respiration increased linearly with increasing DO concentration; however, there was no effect on leaf net CO₂ exchange rate. It is suggested that it was safe to enrich root zone DO to as high as 30 mg L⁻¹, although the growth benefit was minor by increasing DO from ambient air saturated level (∼8.5 mg L⁻¹) to 30 mg L⁻¹. Higher than 30 mg L⁻¹ could cause reduction in tomato plant growth.     

Use of a cyclic high-pressure sodium lamp to inhibit flowering of chrysanthemum and velvet sage

Photoperiod is commonly controlled in the commercial production of ornamental crops to induce or prevent flowering. Flower induction in short-day (SD) plants can be prevented or delayed when the natural daylength is short by providing low-intensity lighting during the dark period. A stationary high-pressure sodium (HPS) lamp with an oscillating aluminum parabolic reflector (cyclic HPS) has been developed to provide intermittent lighting to greenhouse crops. We determined the efficacy of a cyclic HPS lamp at preventing flowering in SD plants garden chrysanthemum [Chrysanthemum × grandiflorum (Ramat.) Kitam.] ‘Bianca’, pot chrysanthemum ‘Auburn’, and velvet sage (Salvia leucantha L.) relative to traditional night interruption (NI) lighting strategies. Plants were grown in a glass-glazed greenhouse at a mean daily temperature of 19.5–20.7 °C with natural SD photoperiods. NI lighting was delivered during the middle of the night (2230–0230 h) from a 600 W cyclic HPS lamp mounted at one gable end of the greenhouse or from incandescent (INC) lamps that were illuminated for the entire 4 h (CONT INC) or for 6 min every 30 min for 4 h. Plants under cyclic HPS were grown at lateral distances of 1, 4, 7, 10, or 13 m from under the lamp. Control plants were grown under an uninterrupted 15 h skotoperiod. As the distance from the cyclic HPS lamp increased from 1 to 13 m, the maximum irradiance measured during the NI decreased from 25.4 to 0.3 μmol m⁻² s⁻¹ and time to visible inflorescence (VI) and the number of nodes at VI decreased. All species had a VI within 54 d, but ≤10% of plants flowered when grown at a lateral distance of 1 or 4 m from the cyclic HPS lamp or under CONT INC. Plants grown without NI had a VI 2 to 15 d earlier and flowered 7 to 24 d earlier than plants grown at 10 or 13 m from the cyclic HPS. All garden chrysanthemums flowered under cyclic INC, whereas velvet sage and pot chrysanthemum had 15% and 35% flowering, respectively. These results indicate that a cyclic HPS lamp can be used effectively to delay flower induction and prevent flowering in these species when NI is delivered at ≥2.4 μmol m⁻² s⁻¹.     

Growth and photosynthetic characteristics of blueberry (Vaccinium corymbosum cv. Bluecrop) under various shade levels

Blueberry can readily be shaded as a bush type plant, maybe affecting its growth and photosynthesis. Growth and photosynthetic characteristics of ‘Bluecrop’ blueberry grown under various shade levels were investigated to understand acclimation under shade conditions and to determine the optimal light conditions for agricultural purpose. Shade decreased the number of shoots per shrub, but increased shoot length. However, shade did not affect the number of leaves on the main axis. With increasing shade level, leaf length, width and area increased, but leaf thickness decreased. However, there was no obvious tendency in leaf length/width ratio with increasing shade level. Shade leaves had less dense stomata than sun leaves, but stoma was bigger in shade leaves than in sun leaves. With increasing shade level, non-photochemical quenching in blueberry leaves increased and the values were higher at low photosynthetic photon flux densities (PPFDs) in shade leaves than in sun leaves, resulting in the decreases in quantum yield, electron transport rate and net CO₂ assimilation rate (A_n). The maximum A_n at 31, 60, 73 and 83% shade levels was 11.8, 11.0, 8.4 and 7.5 μmol m⁻² s⁻¹, respectively. Following the slight decrease up to 100 μmol m⁻² s⁻¹ PPFD, stomatal conductance (g_s) linearly increased up to 600 μmol m⁻² s⁻¹ PPFD and became saturated at all shade levels. The leaves of the shrubs grown under the 83% shade level had a significantly lower g_s as compared to the leaves of the shrubs grown under the 31, 60 and 73% shade levels. Transpiration rate (E) linearly increased up to 600 μmol m⁻² s⁻¹ PPFD and was saturated at the 73 and 83% shade levels. However, E increased linearly at both 31 and 60% shade levels with increasing PPFD. The reproductive growth characteristics such as number of flowers, fruit set rate per flower bud and fruit yield also significantly decreased with increasing shade level. For agricultural purpose, therefore, shade level above approximately 60% of full sunlight must be avoided for optimal photosynthesis and growth of the ‘Bluecrop’ blueberry.     

CO2 and air circulation effects on photosynthesis and transpiration of tomato seedlings

In the daytime, a CO₂ depletion of 10–15% and air circulation of less than 0.5 m s⁻¹ often occur in a naturally ventilated greenhouse during a sunny day with high wind speed (3–5 m s⁻¹). We, therefore, investigated the effects of moderate increase of the CO₂ concentration above the atmospheric level (500–600 μmol mol⁻¹) and air circulation up to 1.0 m s⁻¹ in a growth chamber on the net photosynthetic and transpiration rates of tomato seedlings as the first step. The average net photosynthetic rates were 2.1, 1.8, and 1.6 times higher in the growth chambers with increased CO₂ concentration (500–600 μmol mol⁻¹) and air circulation (1.0 m s⁻¹), increased CO₂ concentration, and increased air circulation, respectively, compared with those in the control (no increase in CO₂ concentration (200–300 μmol mol⁻¹) or air circulation (0.3 m s⁻¹). The transpiration rate increased with increased air circulation, while it decreased with increased CO₂ concentration regardless of air circulation. From the results, we consider that increasing the CO₂ concentration and/or air circulation in ventilated greenhouses up to the outside concentration (350–450 μmol mol⁻¹) and 1.0 m s⁻¹, respectively, can significantly increase the net photosynthetic rate of greenhouse plants.     

Temperature and photoperiod control of morphology and flowering time in two greenhouse grown Hydrangea macrophylla cultivars

Knowledge of the factors involved, and tools to control morphology and flowering are important in intensive and cost-efficient greenhouse production. Hydrangea macrophylla is an important flowering pot plant in Norway and is produced year-around in greenhouses. Due to problems in scheduling, a study was conducted to compare floral transition and morphology of two commercially important cultivars of Hydrangea (‘Early Blue’ and ‘Schneeball’) under different flower initiating treatments in growth chambers. Plants were grown with high pressure sodium lamps (HPS) at moderate temperature (17 °C) (MT) and high (24 °C) temperature. At high temperature, the effect of (1) irradiance under long day conditions (16 h lighting with 70 or 200 μmol m⁻² s⁻¹), and (2) short day (8 h lighting) was investigated. The short day treatment had similar light integral as the low irradiance long day treatment (SD: 8 h × 140 μmol m⁻² s⁻¹ and LD: 16 h × 70 μmol m⁻² s⁻¹ = 4.0 mol m⁻² d⁻¹). The intention was to test the effect of irradiance and SD on flower transition and morphology under high temperatures. The results clearly showed that MT is the strongest signal for floral transition. MT resulted in a rapid floral transition of the terminal buds and lateral flower buds. A short forcing period was required and the plants became short and compact without any use of chemical growth retardants. At high temperatures only SD had a promotive effect on flower transition and the response was found to be stronger in ‘Schneeball’ than ‘Early Blue’. In general, all the treatments under high temperatures required a long forcing time and the plants tended to be very tall with a low number of lateral flower buds.     

Light quality of continuous illuminating at night to induce floral initiation of Fragaria chiloensis L. CHI-24-1

A wild strawberry strain, Fragaria chiloensis CHI-24-1, produced inflorescences from both parent and asexually propagated daughter plants linked with runners when grown at 23 °C/20 °C (day/night) under a 24 h day-length (DL) of daylight plus nightly lighting by an incandescent lamp, but not under 8 or 16 h DLs. In the present study, the effect of light quality for continuous illuminating at night on floral initiation of CHI-24-1 plants grown under a 24 h DL was examined. The CHI-24-1 plants were grown under a 24 h DL consisting of natural daylight and continuous lighting at night by an incandescent, a blue fluorescent, a red fluorescent or a far-red fluorescent lamp for 40 days in summer and autumn. Also, the CHI-24-1 plants were grown for 40 days in a growth chamber at 25 °C/20 °C (day/night) with natural daylight and continuous lighting at night by red- and four types of far-red light-emitting-diodes (LEDs with peak wavelengths of 660, 700, 735, 780 and 830 nm). In both experiments, floral initiation of the parent and daughter plants was observed under a stereomicroscope. Although more than 50% of the parent and daughter plants initiated flower buds under the incandescent and far-red fluorescent lamps, about 15% and 0% of those initiated flower buds under blue and red fluorescent lamps, respectively. Floral initiation of the parent and daughter plants occurred under the far-red LED light source whose peak wavelength was 735 nm, but not under the red or the other far-red LEDs. From these results, it can be concluded that the effective light wavelength range of nightly continuous illuminating for floral induction in the CHI-24-1 plants is 735 nm in the far-red light region. Hence, the induction of floral initiation by nightly continuous far-red light (735 nm) appeared to be a response mediated by phytochrome.     

Nursery inoculation of tomato with arbuscular mycorrhizal fungi and subsequent performance under irrigation with saline water

Protected horticultural crops as well as those planted in open fields particularly in the Mediterranean region have to cope with increasing salinization of irrigation water. High salinity of the supply water has detrimental effects on soil fertility and plant nutrition and reduces crop growth and yield. This study was conducted to determine if pre-inoculation of transplants with arbuscular mycorrhizal (AM) fungi alleviates salt effects on growth and yield of tomato (Lycopersicon esculentum Mill. Cv. Marriha) when irrigated with saline water. Tomato seeds were sown in polystyrene trays with 20 cm³ cells and treated with AM fungi (AM) or without (nonAM) Glomus mosseae. Once the seedlings were reached appropriate size, they were transplanted into nonsterile soil in concrete blocks (1.6 m × 3 m × 0.75 m) under greenhouse conditions. The soil electrical conductivity (EC_e) was 1.4 dS m⁻¹. Plants were irrigated with nonsaline water (EC_w = 0.5 dS m⁻¹) or saline water (EC_w = 2.4 dS m⁻¹) until harvest. These treatments resulted with soil EC at harvest 1.7 and 4.4 dS m⁻¹ for nonsaline and saline water treatments, respectively. Root colonization with AM fungi at flowering was lower under saline than nonsaline conditions. Pre-inoculated tomato plants with AM fungi irrigated with both saline and nonsaline water had greater shoot and root dry matter (DM) yield and fruit fresh yield than nonAM plants. The enhancement in fruit fresh yield due to AM fungi inoculation was 29% under nonsaline and 60% under saline water conditions. Shoot contents of P, K, Zn, Cu, and Fe were higher in AM compared with nonAM plants grown under nonsaline and saline water conditions. Shoot Na concentrations were lower in AM than nonAM plants grown under saline water conditions. Results indicate that pre-inoculation of tomato transplants with AM fungi improved yield and can help alleviate deleterious effects of salt stress on crop yield.     

Modeling plant morphology and development of petunia in response to temperature and photosynthetic daily light integral

The effects of mean daily temperature (MDT) and mean photosynthetic daily light integral (MDLI) on flowering during the finish stage of two petunia (Petunia × hybrida) cultivars were quantified. Petunia ‘Easy Wave Coral Reef’ and ‘Wave Purple’ were grown in glass-glazed greenhouses at 14–23 °C or 14–26 °C and under 4–19 mol m⁻² d⁻¹ with a 16-h photoperiod. The flower developmental rate was predicted using a model that included a linear MDT function with a base temperature multiplied by an exponential MDLI saturation function. The flower developmental rate increased and time to flower decreased as MDT increased within the temperature range studied. For example, under a MDLI of 12 mol m⁻² d⁻¹, as MDT increased from 14 to 23 °C, time to flower of ‘Easy Wave Coral Reef’ and ‘Wave Purple’ decreased from 51 to 22 d and 62 to 30 d, respectively. Flower developmental rate increased as MDLI increased until saturation at 14.1–14.4 mol m⁻² d⁻¹. Nonlinear models were generated for effects of MDT and MDLI on flower bud number and plant height at flowering. The number of flower buds at flowering increased as MDT decreased and MDLI increased. For example, at an MDT of 14 °C with 18 mol m⁻² d⁻¹, plants had 2.5–2.9 times more flower buds than those grown at 23 °C and 4 mol m⁻² d⁻¹. Models were validated with an independent data set, and the predicted time to flower, flower bud number, and plant height were within ±7 d, ±20 flowers, and ±4 cm, respectively, for 96–100%, 62–87%, and 93–100% of the observations, respectively. The models could be used during greenhouse crop production to improve scheduling and predict plant quality of these petunia cultivars.     

The effects of foliar applied CaCl2·2H2O,Ca(OH)2 and K2CO3 combined with the surfactants Glucopon and Plantacare on gas exchange of 1 year old apple (Malus domestica BORKH.) and broad bean (Vicia faba L.) leaves

Calcium chloride, calcium hydroxide, potassium carbonate and the alkylpolyglycoside surfactants Glucopon 215 CSUP and Plantacare 12 UP are salts applied to leaves as foliar nutrients and fungicides. These chemicals were sprayed on apple (Malus domestica BORKH.) and broad bean (Vicia faba L.) leaves. Stomatal conductance and rates of net photosynthesis were measured continuously in the light and in the dark using a Portable Photosynthesis System CIRAS-1. All compounds with the exception of Ca(OH)₂ affected stomatal conductance and net photosynthesis, albeit to different degrees. In light, Plantacare either alone (0.2 g l⁻¹) or in combination with CaCl₂·2H₂O (5 g l⁻¹) or K₂CO₃ (5 g l⁻¹) caused a rapid initial increase in stomatal conductance during the first 1–3 h after spraying on the leaves, maximum conductances were observed about 6 h after application. A rather high stomatal conductance was observed during the dark period when Glucopon (0.2 g l⁻¹) was applied either alone or in combination with Ca(OH)₂. The combination CaCl₂·2H₂O + Glucopon did not cause this elevated stomatal conductance during the dark. CaCl₂·2H₂O reduced stomatal conductance in combination with both Glucopon and Plantacare. The surfactant Plantacare reduced net photosynthesis during the first light period (12 h), if applied alone or in combination with CaCl₂·2H₂O. Treatment of broad bean leaves with K₂CO₃ + Plantacare resulted in a rapid decrease in net photosynthesis during the first hour, and then the rates of net photosynthesis increased rapidly and approached to those of the water control. The effects of surfactants and salts on net photosynthesis had nearly disappeared by the beginning of the second light period. Non-specific glycosidases presumably cleaved the glycosidic bond between the alkyl and the sugar moieties during the preceding night. Our data showed that foliar applications of CaCl₂·2H₂O and K₂CO₃ together with alkyl polyglycoside surfactants can affect gas exchange. However, the effects of the chemicals at the concentrations used in our study were not very large and were transient. They practically vanished within 24 h and a detrimental effect on growth and development of crops was not likely.     

The effect of organic supplementation of solarized soil on the quality of tomato fruit

Soil solarization, used to control weeds and soil-borne pathogens in hot climates, has not yet been widely adapted as a commercial practice because of its lack of efficacy. Experiments were carried out in southern Italy over two growing seasons to study the effect of three levels (0, 0.35 and 0.7 kg m⁻²) of organic supplementation of the soil prior to solarization on soil mineral availability and fruit quality attributes. Soil temperature and chemical properties were monitored, together with changes in the physical characteristics and chemical composition of tomato fruits grown under commercial greenhouse conditions. Organic supplementation increased the soil temperature achieved through solarization by 3.9 to 5.5 °C. Organic supplementation increased (P ≤ 0.05) the soil concentration of NO₃⁻-N, exchangeable K₂O, Ca²⁺, Na⁺ and Mg²⁺ and the level of electrical conductivity in the soil extract. Physical characteristics of tomato fruits were improved by supplementation, with fresh and dry weight enhanced up to 11 and 21%, respectively, mesocarp thickness up to 19%, firmness up to 36% and skin redness (a^*/b^* ratio) up to 24%. As the supplementation rate was raised from 0 to 0.7 kg m⁻², the fruit content of reducing sugars increased (P ≤ 0.01) from 1.75 to 2.14 g per 100 g f.w., ash from 0.49 to 0.62%, soluble solid from 5.12 to 6.18 °Brix, titratable acidity from 0.16 to 0.19%, and ascorbic acid from 25.1 to 32.5 mg 100 mL⁻¹. We concluded that organic supplementation appears to be a valuable and environmentally friendly way to improve the mineral availability in the soil and improve fruit quality of tomato.     

Effects of leaf aging and light duration on photosynthetic characteristics in a cucumber canopy

Photosynthetic characteristics, chlorophyll index and leaf area were examined in selected leaves of cucumber (Cucumis sativus L. cv. Euphorbia). In the first experiment, plants of cucumber were grown horizontally at a lighting period of 20 h day⁻¹. Photosynthetic measurements in horizontally growing cucumbers showed that there was no decline in photosynthetic capacity when cucumber leaves are developing under good light conditions. In a second experiment, plants were grown in a traditional high-wire cultivation system under 20 h day⁻¹ lighting period until they reached final height and then exposed to different lighting periods (20 and 24 h day⁻¹) for 3 weeks. In stands of cucumber plants photosynthetic measurements showed that the lower leaves have a significant reduction in photosynthetic capacity due to reduced light conditions. Three weeks exposure to 24 h day⁻¹ lighting period reduced leaf area by 20%. Plant grown under continuous light had also lower chlorophyll index compared to plants grown under 20 h day⁻¹ lighting period.     

In vitro multiplication of statice plantlets using sugar-free media

Clumps of statice (Limonium latifolium) plantlets grown photomixotrophically were used as explants and cultured for 25 days on a sugar-free modified Murashige and Skoog (MS) medium in Magenta-type vessels with the number of air exchanges of the vessel (NAE) being 3.8 h⁻¹, at a photosynthetic photon flux (PPF) of 100 μmol m⁻² s⁻¹ and a CO₂ concentration of 1500 μmol mol⁻¹ in the culture room. A factorial experiment was conducted with three levels of 6-benzylaminopurine (BA) concentration, namely 0, 0.25 and 0.5 mg L⁻¹, and two types of supporting material, agar and Florialite (a porous material). The control treatment was a photomixotrophic culture using a sugar- and BA (0.25 mg L⁻¹) containing agar medium in the vessel with NAE of 0.2 h⁻¹, at a PPF of 50 μmol m⁻² s⁻¹ and a CO₂ concentration of 400 μmol mol⁻¹ in the culture room. Leaf area, chlorophyll concentration and net photosynthetic rate were greater in the sugar-free medium treatment with a BA concentration of 0.25 mg L⁻¹ and Florialite than those in the control treatment. The number of shoots and dry weight per clump in the sugar-free medium treatment were comparable to those in the control treatment. Among the sugar-free medium treatments, the number of shoots increased with increasing BA concentration, however, the leaf area, dry weight, chlorophyll concentration and net photosynthetic rate decreased with increasing BA concentration. The use of Florialite significantly enhanced the growth and root induction as well as net photosynthetic rate, compared with the treatments that use agar. These results indicated that sugar-free medium micropropagation could be commercially applied to the multiplication of statice plantlets.     

Plant regeneration of Carica papaya L. through somatic embryogenesis in response to light quality,gelling agent and phloridzin

Difficulties to develop an easy and reproducible protocol to get healthy and well formed plants from somatic embryos of papaya (Carica papaya L.) had included low germination, callus production at the base of the embryo radicle and the occurrence of hyperhydric plantlets among others, and by consequence unsuccessful transfer to the field. With the aim of improving a propagation method, the effects of light quality, gelling agent and phloridzin concentration on the germination of somatic embryos of hermaphrodite C. papaya L. var. Maradol were studied. Somatic embryos were grown on half strength MS medium, with the addition of Chen vitamins [Chen, M.H., Wang, P.J., Maeda, E., 1987. Somatic embryogenesis and plant regeneration in Carica papaya L. tissue culture derived from root explants. Plant Cell Rep. 6, 348–351], solidified with three distinct gelling agents: Sigma^® Agar–Agar, Difco^® Bacto agar and Phytagel^®; supplemented with phloridzin and exposed to different light qualities: blue (54 μmol m⁻² s⁻¹), red (65 μmol m⁻² s⁻¹), gro-lux (68 μmol m⁻² s⁻¹), red + blue, white (32 μmol m⁻² s⁻¹) and wide spectrum (49 μmol m⁻² s⁻¹) during a period of 4 weeks. Results show that light quality and gelling agent had important effects on germination and plant growth, while 3.0 mg L⁻¹ phloridzin had an important role on germination as well as in root development. Somatic embryos exposed to white light, culture medium solidified with 3.0 mg L⁻¹ phytagel and 3.0 mg L⁻¹ phloridzin showed longer roots. Meanwhile, germination and plant length were promoted on an improved culture medium solidified with 7.5 g L⁻¹ Difco^® Bacto agar, 3.0 mg L⁻¹ phloridzin and exposed to gro-lux lamps. Under these conditions, 70% of somatic embryos germinated and developed normal roots without hyperhydricity. The regenerated plantlets with well developed roots and shoots were successfully transferred to a greenhouse with a survival rate of 95%.     

Closed cycle subirrigation with low concentration nutrient solution can be used for soilless tomato production in saline conditions

Closed cycle soilless techniques can be adopted to minimize water and fertilizer losses in greenhouse cultivation. There is a general lack of information regarding the soilless cultivation of vegetables with closed cycle subirrigation techniques, specifically when using saline water. In this study, a trough bench subirrigation system (SUB), with two fertilizer concentrations (“100%”, containing 9.8 mol m⁻³ N-NO₃, 1.6 mol m⁻³ P-H₂PO₄, 8.7 mol m⁻³ K⁺, 2.8 mol m⁻³ Ca⁺, 1.8 mol m⁻³ Mg⁺, 4 mol m⁻³ S-SO₄, and “70%”, containing 70% of the macronutrient concentration) in the nutrient solution (NS), was compared with open cycle drip-irrigation (DRIP with “100%” NS). For all the three treatments, NS was prepared using rain water (0.05 dS m⁻¹) and adding NaCl (1 g L⁻¹), in order to simulate moderate saline irrigation water. The effect of the treatments on tomato (Solanum lycopersicum L.) plant growth, yield, fruit quality, water use efficiency (WUE) and fertilizer consumption was evaluated. Substrate and recirculating NS composition were also studied. Subirrigation, regardless of NS concentration, reduced plant height (by 30 cm), leaf area (by 1411 cm²), total fresh and dry weight (by 429 and 48.5 g plant⁻¹, respectively) but not dry matter percentage of the whole plant, with respect to DRIP. Yield was reduced when plants were subirrigated with the higher concentrated NS, but no differences with open cycle DRIP were recorded when the lower NS concentration was used in SUB. Fruit quality was not affected by irrigation system or NS concentration. The higher WUE was obtained with subirrigation. NaCl accumulated similarly over the crop cycle in recirculating NS of both SUB treatments and in growing substrates of all the three treatments. Higher salt concentration was found in subirrigated substrates, in particular in the upper part of the substrate profile. Fertilizers accumulated in the subirrigated substrates when the higher NS concentration was used, but not when the NS concentration was reduced by 30%. The results of this study indicate that tomato can be grown successfully in a closed cycle subirrigation system, using saline water, by reducing the fertilizer NS concentration normally used with traditional open cycle systems.     

High frequency early flowering from in vitro seedlings of Dendrobium nobile

Dendrobium nobile Lindl. is a popular temperate Chinese orchid commonly marketed as a traditional medicinal plant. Seedlings of Dendrobium nobile Lindl. produced floral buds (33.3–34.8%) precociously on a defined basal medium (1/2 MS) containing paclobutrazol (PP₃₃₃) at 0.5 mg L⁻¹ or thidiazuron (TDZ) at 0.1 mg L⁻¹ within 4 months of culturing. The frequency of floral buds formation can be further increased to 95.6% by growing seedlings in a PN (PP₃₃₃ 0.3 mg L⁻¹ + NAA 0.5 mg L⁻¹)-containing medium followed by transfer onto 1/2 MS medium with PP₃₃₃ and TDZ (PP₃₃₃ + TDZ). However, flower developed was deformed under 25 °C but it developed fully when grown in a lower temperature regime (23 °C/18 °C, light/dark) for 45 days. Under optimal condition, in vitro flowering was observed about 6 months after seed sowing.