Effect of electrical conductivity and transpiration on production of greenhouse tomato (Lycopersicon esculentum L.)

We investigated the hypothesis that manipulating water out-flow of a plant through the shoot environment (potential transpiration, ET₀) in a glasshouse could modulate the effect of salinity/osmotic potential in the root environment upon yield of tomatoes. Contrasting root-zone salinity treatments were combined with two climate treatments — a reference (high transpiration, HET₀) and a “depressed” transpiration (low transpiration, LET₀). The salinity treatments, characterised by their electrical conductivity (EC) were 6.5, 8 and 9.5 dS m⁻¹, were always coupled with a reference treatment of EC=2 dS m⁻¹. In another experiment, concentrated nutrients (Nutrients) and nutrients with sodium chloride (NaCl) at the same EC of 9 dS m⁻¹ were compared.Marketable fresh-yield production efficiency decreased by 5.1% for each dS m⁻¹ in excess of 2 dS m⁻¹. The number of harvested fruits was not affected; yield loss resulted from reduced fruit weight (3.8% per dS m⁻¹) and an increased fraction of unmarketable harvest. At the LET₀ treatments, yield loss was only 3.4% per dS m⁻¹ in accordance with the reduction in fruit weight. Low transpiration did increase fruit fresh yield by 8% in both NaCl and Nutrients treatments at an EC=9 dS m⁻¹. Neither EC nor ET₀ affected individual fruit dry weight. Accordingly, fruit dry matter content was significantly higher at high EC than in the reference (4% per each EC unit in excess of 2 dS m⁻¹) and responded to ET₀ to a minor extent. Control of the shoot environment in a greenhouse to manipulate the fresh weight of the product may mitigate the effects of poor quality irrigation water without affecting product quality.     

Analysis of the effect of EC and potential transpiration on vegetative growth of tomato

This paper analyses the response of vegetative growth of greenhouse tomato to both root-zone salinity and shoot-environment (potential transpiration), with the purpose of explaining the observed lack of effect on dry matter yield. A reference salinity (EC) of 2 dS m⁻¹ was compared in three experiments with, respectively, 6.5, 8 and 9.5 dS m⁻¹. Another experiment investigated specific effects of sodium chloride, by comparing two high-EC treatments (both 9 dS m⁻¹), one with a high concentration of nutrients and one with addition of sodium chloride to a normal nutrient solution. The shoot-environment was either a “normal” climate regime or the same regime but with depressed potential transpiration, mainly by adaptation of the humidity set point. There was no detectable effect of the potential transpiration treatment, neither of the sodium chloride. Salinity effects on vegetative growth only showed up at EC exceeding 6.5 dS m⁻¹. The most evident EC effect was a reduction of leaf expansion; individual leaf area was reduced by 8% per dS m⁻¹ exceeding 6.5. This was partly compensated by a slight increase (2% per unit EC) in the number of leaves, which explains why cumulative plant leaf area decreased by about 7% per unit EC in excess of 6.5 dS m⁻¹. Therefore, leaf area index (LAI) at the highest EC was reduced by some 20% compared to the LAI at an EC of 2 dS m⁻¹. It is estimated that this would cause a reduction of less than 8% in light interception, and thus in dry matter produced. Indeed, differences observed in dry weight between the EC treatments were never significant.     

Estimation of broad-leaved canopy growth in the urban forested area using multi-temporal airborne LiDAR datasets

Inter-annual canopy growth is one of the key indicators for assessing forest conditions, but the measurements require laborious field surveys. Up-to-date LiDAR remote sensing provides sufficient three-dimensional morphological information of the ground to monitor canopy heights on a broad scale. Thus, we attempted to use multi-temporal airborne LiDAR datasets in the estimation of vertical canopy growth, across various types of broad-leaved trees in a large urban park.The growth of broad-leaved canopies in the EXPO '70 urban forest in Osaka, Japan was assessed with 19 plots at the stand level and 39 selected trees at the individual-tree level. Airborne LiDAR campaigns repeatedly observed the park in the summers of 2004, 2008, and 2010. We acquired canopy height models (CHMs) for each year from the height values of the uppermost laser returns at every 0.5 m grid. The annual canopy growth was calculated by the differences in CHMs and validated with the annual changes in field-measured basal areas and tree heights.LiDAR estimations revealed that the average annual canopy growth from 2004 to 2010 was 0.26 ± 0.11 m m⁻² yr⁻¹ at the plot level and 0.26 ± 0.10 m m⁻² yr⁻¹ at the individual-tree level. This result showed that growing trends were consistent at different scales through 2004 to 2010 despite uncertainty in estimating short-term growth for small crown areas at the individual-tree level. This LiDAR-estimated canopy growth shows a moderate relation to field-measured increase of basal areas and average heights. The estimation uncertainties seem to result from the complex canopy structure and irregular crown shape of broad-leaved trees. Challenges still remain on how to incorporate the growth of understory trees, growth in the lateral direction, and gap dynamics inside the canopy, particularly in applying multi-temporal LiDAR datasets to the large-scale growth assessment.     

Analysis of rhythmic growth in holly (Ilex × meserveae) grown in controlled conditions

The influence of 24 h mean air temperature (18.3, 20.6, 23.9 and 25.8 °C) and photosynthetic photon flux (PPF; 0.6, 2.1, 3.7 and 4.7 mol m⁻² d⁻¹) on the growth cycles of vegetative growth in Ilex × meserveae (‘Blue Princess’ S.Y. Hu) was investigated. Plants propagated from top cuttings were grown in greenhouse compartments. The number of unfolded leaves was recorded continuously throughout the experiment. A modified sine function was fitted to collected data and the values for the amplitude and frequency of the growth curves were analysed. The sine function was tested as a method to evaluate the influence of climate on periodically flushing species. Both amplitude and frequency were significantly influenced by air temperature and PPF. The highest frequency of flushing was found at 23.9 °C and 3.7 mol m⁻² d⁻¹. The function resulted generally in a good fit to collected data with R² values above 0.9. Growth curves of all individual plants were categorised with respect to their growth pattern as poor synchronisation within the treatments did not allow analysis of the mean values of the growth curves.     

The impact of photoperiod and irradiance on flowering of several herbaceous ornamentals

Forty-one herbaceous species were grown under short-days (8 h photoperiod, ambient irradiance averaged 12–13.2 and 6.4–8.3 mol m⁻² day⁻¹ for Experiments I and II, respectively) with or without supplemental high-pressure sodium lighting (+50, 100, or 150 μmol m⁻² s⁻¹); or under long-days delivered using natural day lengths and irradiance with night interruption lighting (2200–0200 h at 2 μmol m⁻² s⁻¹ from incandescent lamps) or under ambient daylight plus supplemental irradiance during the day and as a day extension to 18 h (0800–0200 h) with supplemental high pressure sodium lighting (+50, 100, or 150 μmol m⁻² s⁻¹) to identify the impact of photoperiod and irradiance on flowering of each species. Days to first open flower, leaf number below first flower, and mean dry weight gain per day (MDWG) were measured when the first flower opened. Twenty-seven species were photoperiodic with examples of five photoperiodic response groups represented: obligate short-day (2), facultative short-day (5), obligate long-day (16), facultative long-day (4); 13 were day neutral (no photoperiod response in flowering). One species, Salvia sclarea L., did not flower. A facultative irradiance response was observed with 10 species; 28 species were irradiance indifferent; 2 had delayed flowering as irradiance increased. Photoperiod affected MDWG of 30 species. Increasing irradiance affected MDWG with 14 species. Photoperiod interacted with irradiance to affect MDWG of 11 species. Cobaea scandens had the greatest MDWG (0.40 g day⁻¹) while Amaranthus hybridus had the least MDWG (0.01 g day⁻¹) across photoperiod and irradiance levels.     

Predicting dry matter production of cauliflower (Brassica oleracea L. botrytis) under unstressed conditions: I. Photosynthetic parameters of cauliflower leaves and their implications for calculations of dry matter production

Measurements of CO₂ exchange of cauliflower leaves were carried out in a field experiment which included two nitrogen fertilisation rates. Irradiance and CO₂ concentration were varied at the leaf level within a leaf cuvette and additionally a temperature treatment was applied to field grown plants moved into climate chambers. These measurements were used to estimate parameter values of a rectangular hyperbola describing cauliflower leaf CO₂ exchange as a function of irradiance and CO₂ concentration. The obtained parameter estimates were used to derive empirical regression equations with temperature and nitrogen content of the leaves as independent variables. The resulting relationships were applied within a simple photosynthesis–respiration based dry matter production model in order to derive functional relationships between light use efficiency and irradiance, leaf area index and temperature.The rectangular hyperbola was able to describe the gas exchange data as varied by irradiance and CO₂ concentration on the single leaf level with sufficient accuracy, but estimates of initial light use efficiency (about 25 μg J⁻¹) were too high because of the bias emanating from the limited flexibility of this model. Light saturated photosynthesis rate (P_max) showed an optimum response to temperature and an increase with increasing nitrogen content of leaves. The initial slope α of the rectangular hyperbola showed no consistent responses to ambient temperature and nitrogen content of leaves. The respiration per unit leaf area β increased exponentially with increasing temperature, resulting in a Q₁₀ value of 1.86. Because only a limited number of plants was evaluated in this study, additional work is needed to further substantiate the results of the gas exchange measurements.The model analysis demonstrated that LUE is independent of the light integral over a range 5–10 MJ m⁻² per day photosynthetically active radiation if one assumes an adaptation of P_max within the canopy and over time according to the incident irradiance. Acclimatisation within the canopy and higher leaf area indices, LAI, reduce the decrease of LUE with irradiance but a substantial decline remains even for LAI values of 4.     

The effects of NaCl pre-treatments on salt tolerance of melons grown under long-term salinity

The response of melon (Cucumis melo) plants to long-term salinity was investigated to determine the availability of the NaCl pre-treatments (seed priming + seedling conditioning) as an interesting strategy for increasing the salt tolerance. Seeds of melon cultivars “Hasanbey” and “Kirkagac” were primed with 18 dS m⁻¹ NaCl solution for 3 days at 20 °C. During emergence and seedling growth, non-primed seeds were irrigated with local irrigation water (EC: 0.3 dS m⁻¹) whereas primed groups were treated with 9.0 dS m⁻¹ saline solution for 35 days. Seedlings derived from pre-treated (P) and non-pre-treated (NP) groups were transplanted to 8 l pots. After transplanting, salinity treatments were started with the first irrigation. The salinity treatments consisted of five levels (control, 4.5, 9.0, 13.5 and 18.0 dS m⁻¹) of irrigation solution for a period of 90 days. NaCl pre-treatments diminished the inhibiting effect of salinity on growth of melon plants. However, competence for salt adaptation varied with cultivar and the level of salinity. The physiological response of the P plants was also maintained in the long-term. Stomatal conductance and relative chlorophyll content of P plants tended to be higher than those of the NP ones. In addition, NaCl pre-treatments enhanced K and Ca concentrations of leaves and stems, and prevented toxic effects of salinity because less Na accumulated in stems. These results suggest that the use of NaCl pre-treatments could be a useful strategy to increase the salt tolerance of melon plants in the long-term and also to permit the establishment of melon crop by direct sowing in a saline medium.     

Comparison of growth,leaf water relations and gas exchange of Cistus albidus and C. monspeliensis plants irrigated with water of different NaCl salinity levels

Four-month-old potted Cistus albidus and Cistus monspeliensis plants growing in a greenhouse were submitted to saline stress from 9 August to 2 December, using irrigation water containing 0, 70, and 140 mM NaCl. C. monspeliensis plants are more tolerant to saline irrigation water than C. albidus plants, mainly due to their capacity to resist stress with a lower plant biomass and canopy area; furthermore, they showed no leaf necrosis symptoms. Under saline stress conditions the main growth limiting factor in both species was photosynthesis. Both Cistus species responded to saline stress by developing avoidance and tolerance mechanisms. The avoidance mechanisms took place at a morphological and physiological level. Morphologically, the reduction in the canopy area can be considered a mechanisms for regulating water loss via transpiration. Treated C. monspeliensis plants showed a greater capacity to absorb water and were able to conserve it more efficiently than C. albidus plants. Tolerance mechanisms included Na⁺ and Cl⁻ inclusion and osmotic adjustment. However, the reaction of each species to osmotic adjustment was different, because in C. monspeliensis plants the osmotic adjustment was unable to prevent a decrease in leaf turgor. The curvilinear relationship between P_n and g_l observed in C. monspeliensis plants indicated stomatal limitation of photosynthesis below a leaf conductance of about 160 mmol m⁻² s⁻¹. In C. albidus plants, a linear relationship between photosynthesis and leaf conductance rather a curvilinear model was significant, indicating limitation of the photosynthetic capacity.     

Net CO2 exchange rate of in vitro plum cultures during growth evolution at different photosynthetic photon flux density

CO₂ concentration was monitored during three 15-day subculturing cycles in vessels containing actively proliferating plum cultures of Prunus cerasifera, clone Mr.S. 2/5. The effects of two photosynthetic photon flux density regimes: 50 ± 5 μmol m⁻² s⁻¹ and 210 ± 5 μmol m⁻² s⁻¹ were compared. Three distinct phases in the CO₂ trend were distinguished during each culturing cycle of both light treatments. In the first, occurring at the beginning of the culture cycle, the amount of CO₂ emitted by the cultures during dark periods was greater than that assimilated during the light periods. In the second phase, the opposite trend was detected, while in the third, the range of CO₂ day–night fluctuations increased or remained stable according to the number of explants per vessel. The treatment with 210 ± 5 μmol m⁻² s⁻¹ did not modify the CO₂ phase trend but induced more pronounced fluctuations in day–night CO₂ concentration. Under this light treatment, cultures reached CO₂ compensation point for a period as long as 48% of the total number of light hours, while under 50 ± 5 μmol m⁻² s⁻¹, it was only 8%. The different range in CO₂ day–night fluctuations monitored throughout a subculturing cycle, appeared to be mainly induced by changes in culture growth dynamics.     

Growth,gas exchange,and nutrient status in pepper (Capsicum annuum L.) grown in recirculating nutrient solution as affected by salinity imposed to half of the root system

Pepper plants grown in recirculating nutrient solution were exposed to NaCl-salinity (60 mM NaCl, 8 dS m⁻¹) imposed either to the entire or to half of the root system and compared to plants supplied with a standard nutrient solution (1.9 dS m⁻¹). The saline solution was obtained by adding NaCl to the standard nutrient solution. In the split-root treatment, the root compartment not exposed to salinity was supplied with raw water (0.38 dS m⁻¹). Both the stem and the root dry weights were markedly restricted by salinity, irrespective of salinizing half or the entire root system. In the split-root treatment, the dry weight of the root compartment receiving raw water did not differ significantly from that exposed to salinity. The net photosynthesis and the leaf chlorophyll content were restricted by both salinity treatments, but the decrease was more marked when the entire root system was exposed to salinity. In contrast, the stomatal conductance and the transpiration rate were equally reduced, regardless of salinizing the entire or part of the root system. The leaf Na and Cl concentrations were raised by the NaCl-salinity, but only in one sampling date the increase was significantly higher when the entire root zone was exposed to salinity, as compared with salinization of half of the root system. Salinity reduced significantly the leaf K, Ca, and Mg uptake but not to levels that could cause nutrient deficiencies. These results indicate that pepper is susceptible to high salinity, predominantly due to reduced stomatal conductance. However, after long-term exposure to salinity the growth may be suppressed due also to inhibition of photosynthesis at chloroplast level. The adverse effects of high NaCl-salinity are hardly mitigated when only a part of the root system is salinized, which indicates that the response is governed by root exposure to high NaCl concentrations and not by inefficiency of the roots to take up water.     

Seasonal changes in CO2 assimilation in leaves of five major Greek olive cultivars

Leaf CO₂ assimilation rate, stomatal conductance (g_s), internal CO₂ concentration (C_i), chlorophyll (a + b) content, specific leaf weight (SLW) and stomatal density were measured during the season, under field conditions, for five major Greek olive cultivars, ‘Koroneiki’, ‘Megaritiki’, ‘Konservolia’, ‘Lianolia Kerkiras’, and ‘Kalamon’, with different morphological and agronomic characteristics and diverse genetic background. Measurements were taken from current-season and 1-year-old leaves, and from fruiting and vegetative shoots, throughout the season, from March to November in years 2001 and 2002. CO₂ assimilation rates showed a substantial seasonal variation, similar in all cultivars, with higher values during spring and autumn and lower values during summer and late autumn. Stomatal conductance (g_s) followed similar trends to leaf CO₂ assimilation rates, increasing from March to July, following by a decrease during August and increasing again in autumn. ‘Koroneiki’ had the highest leaf CO₂ assimilation rate and g_s values (21 μmol m⁻² s⁻¹ and 0.45 mol m⁻² s⁻¹, respectively) while ‘Lianolia Kerkiras’ and ‘Kalamon’ showed the lowest leaf CO₂ assimilation rate and g_s values (13–14 μmol m⁻² s⁻¹ and 0.22 mol m⁻² s⁻¹, respectively). One-year-old leaves had significantly higher leaf CO₂ assimilation rate than current-season leaves from April to June, for all cultivars. From August and then, leaf CO₂ assimilation rate in current-season leaves was higher than in 1-year-old leaves. There were no significant differences in leaf CO₂ assimilation rate between fruiting and vegetative shoots. Total chlorophyll (a + b) content increased with leaf age in current-season leaves. In 1-year-old leaves chlorophyll content increased in spring, then started to decrease and increased slightly again late in the season. Chlorophyll content was higher in 1-year-old leaves than in current-season leaves throughout the season. Total specific leaf weight (SLW) increased throughout the season for all cultivars. Stomatal density in lower leaf surface was lowest for ‘Koroneiki’ (399 mm⁻²) and highest for ‘Megaritiki’ (550 mm⁻²). Our results showed differences in leaf CO₂ assimilation rate among the five different olive cultivars, with a diverse genetic background, ranging from 12 to 21 μmol m⁻² s⁻¹. From the five cultivars examined, ‘Koroneiki’, a drought resistant cultivar, performed better and was able to maintain higher leaf CO₂ assimilation rate, even under high air vapor pressure deficit. All cultivars had a pronounced seasonal variation in leaf CO₂ assimilation rate, affected by date of the year, depending on ambient conditions. The high temperatures and high air vapor pressure deficit occurring during summer caused a reduction in leaf CO₂ assimilation rate in all cultivars. Leaf CO₂ assimilation rate was also affected by leaf age for all cultivars, with old leaves having significantly higher leaf CO₂ assimilation rate than young leaves early in the season.     

Daylength and photon flux density influence the growth regulator effects on morphogenesis in epicotyl segments of Troyer citrange

The optimal growth regulator addenda for adventitious shoot regeneration in epicotyl cuttings of Troyer citrange (Citrus sinensis×Poncirus trifoliata) varied with the conditions of illumination. The response to illumination and to growth regulators differed for the direct and the indirect (through callusing) pathways of regeneration. Shoot formation through the direct organogenic pathway decreased as the concentration of benzyladenine (BA) in the medium was increased in the range 2.2–22 μM, when the explants were incubated in the dark or under an 8 h daylength. For explants incubated under a 16 h daylength, the number of shoots formed increased with BA concentration. Optimal conditions of incubation for shoot formation through the direct pathway were either an 8 h daylength with a photon flux density of 74 μmol m⁻² s⁻¹ in the presence of 2.2 μM BA, or a 16 h daylength with a photon flux density of 37 μmol m⁻² s⁻¹ in the presence of 22 μM BA. Irrespective of the conditions of incubation, shoot formation through the indirect organogenic pathway was suppressed by the addition of 22 μM BA to the medium. Optimal conditions for shoot formation through this pathway were incubation under an 8 h daylength at a photon flux density of 74 μmol m⁻² s⁻¹ in the presence of 2.2 μM BA. At the optimal conditions indicated, the addition of the synthetic auxin naphtaleneacetic acid (0.54 μM) reduced shoot formation. Irrespective of the pathway of regeneration, the number of shoots formed decreased markedly with the distance of the cutting from the cotyledonary node.     

Rose productivity and physiological responses to different substrates for soil-less culture

Cultivation of roses in various soil-less media was studied with the aim to identify the optimum soil condition for rose production. Madelon roses grafted on rootstock of Rosa indica var. major were transplanted to polyethylene bags containing zeolite and perlite (at ratios of 25z:75p, 50z:50p, 75z:25p and 100z:0p, v/v) in a climate-controlled greenhouse. Net photosynthesis (A_net), stomatal conductance (g_s) and water use efficiency (WUE) of roses were followed for 5 months. Flower production and quality were recorded in three flowering flushes during a 5-month period. Analysis of variance of repeated measurements showed that even though the overall A_net did not differ among treatments (average 18.7 μmol m⁻² s⁻¹), trends in A_net seasonality for roses in 25z:75p substrate differed significantly from those in 50z:50p, 75z:25p or 100z:0p. Stomatal conductance did not show any significant seasonality or trends in response to substrate mixtures, averaging 0.89 mol m⁻² s⁻¹. Water use efficiency was significantly lower for roses in 25z:75p than in 100z:0p mixtures (1.8 ± 0.15 and 2.0 ± 0.13 μmol m⁻² s⁻¹ CO₂/mmol m⁻² s⁻¹ H₂O, respectively). Cumulative production of rose plants did not differ among substrate mixtures. Productivity significantly differed among flower stem classes. Stem class I (>70 cm) and class V (≤30 cm) exhibited the least production, contributing to only 7.6 and 3.7% of the total production, respectively. The highest productivity was observed in classes III (51–60 cm) and IV (31–50 cm), contributing to the bulk of productivity (68.4%). Class II contributed a 20.3% of the production. Results showed that zeolite and perlite acted as inert materials. Zeolite did not exert any positive effect on productivity, in contrast to what has been reported in literature recently. Use of perlite resulted in a little improvement in photosynthesis, however this improvement was not reflected by a significant increase in production.     

Comparison of non-destructive LAI determination methods and optimization of sampling schemes in an open Populus euphratica ecosystem

Populus euphratica (P. euphratica) grows in the water-limited Tarim River Basin in spatially heterogeneous open ecosystems; thus, efforts to quantify the leaf area index (LAI) with optical instruments developed for homogeneous closed canopies have a high probability of failure. In this study, we explored methods for designing an acceptable sampling scheme to quantify the tree LAI for open P. euphratica canopies in arid areas. Field data were collected from three 30 m × 30 m plots and one 100 m × 100 m plot. We compared three indirect methods, i.e. i) allometry, ii) LAI-2000 canopy analyser, iii) Tracing Radiation and Architecture of Canopies (TRAC), and a new semi-direct method combining leaf density and crown volume (SDDV) method for quantifying the isolated tree and canopy LAI of a P. euphratica forest. We also analysed the effects of random and grid sampling designs on the accuracy of the LAI estimates obtained with the LAI-2000. The results showed that the allometric method is applicable to isolated trees with regular shapes; however, because the LAI of P. euphratica was calculated from an allometric equation based on the basal area (at 1.3 m), the allometric equation is prone to failure if the basal area is beyond a specific range. Because there are no significant differences in the plot size between the allometric and the SDDV method predictions, the proposed SDDV method can be used as an alternative for field measurements. The combination of LAI-2000 and TRAC is found to be more reliable than TRAC only, and the field view of the LAI-2000 sensor and the clumping index are important factors for sparse vegetation LAI retrieval. The results from sampling optimization showed that for the LAI-2000 instrument, the best sampling method is grid sampling, and the sampling interval should not be less than 20 m. For random sampling scheme, the number of sampling points in a 100 m × 100 m plot should be greater than 86 with a coefficients of variation of 15% and an allowable error (AE) of 0.15 m² m⁻², respectively.     

Varying evapotranspiration and salinity level of irrigation water influence soil quality and performance of perennial ryegrass (Lolium perenne L.)

Increasing use of recycled water that is often high in salinity warrants further examination of irrigation practices for turfgrass health and salinity management. A study was conducted during 2011–2012 in Riverside, CA to evaluate the response of perennial ryegrass (Lolium perenne L.) ‘SR 4550’ turf to varying quality and quantity of irrigation water. A modified line-source sprinkler irrigation system provided a salinity gradient (EC_w ∼0.6–4.2 dS m⁻¹) in between lines. Irrigation was scheduled in four separate irrigation zones perpendicular to the irrigation lines according to 80, 100, 120, and 140% ET_o. Changes in turf quality (R² = 0.30***), were primarily driven by the number of days that the area had been irrigated with saline water. When data were separated by irrigation amount, both time and water quality accounted for 54% and 46% of the variability (P < 0.001) in quality and cover, respectively at 80% ET_o. A model was created to quantify decline in turf quality in relationship to %ET_o replacement and salinity accumulation in the rootzone (R² = 0.57). Our results suggest that perennial ryegrass requires irrigation scheduling at 140% ET_o, irrigation water quality below EC_w ∼1.7 dS m⁻¹, and EC_e below 3.8 dS m⁻¹ to maintain acceptable quality for 442 d in Riverside, CA.     

Fruit development and ripening in Barbados cherry,Malpighia emarginata DC.

Barbados cherry fruit shows a biphasic pattern of growth whether monitored on a diameter or weight basis. Each growth phase was of about 2 weeks duration with weight gains of equal magnitude but with most of the size increase occurring in the first phase. Pyrene growth paralleled that of the whole fruit. Cell division was limited to the first week of fruit development and horticultural maturity was reached when fruit showed colour break (18 days post-anthesis). Barbados cherry is climacteric with a very high peak respiratory rate (900 ml CO₂ kg⁻¹ h⁻¹) but a low rate of peak ethylene production (3 μl C₂H₄ kg⁻¹ h⁻¹), the former consistent with its high perishability.     

In vitro induction of tetraploid ginger (Zingiber officinale Roscoe) and its pollen fertility and germinability

In vitro induction of tetraploid ginger (Zingiber officinale Roscoe) and its pollen fertility and germinability were investigated. The growth of shoot tip cultures on agar MS medium containing 2.0 mg l⁻¹ BA was greater than that of similar cultures in liquid MS medium with the same BA concentration. In liquid medium, the combinations of 0.5, 1.0, or 2.0 mg l⁻¹ BA with 0.05 mg l⁻¹ NAA tended to enhance the growth of the cultures. The efficiency of tetraploid induction was assessed by treating shoot tip explants on agar or in liquid MS medium containing 2.0 mg l⁻¹ BA, 0.05 mg l⁻¹ NAA, and 0.2% (w/v) colchicine for 4, 8, 12, and 14 days. The total number of tetraploids induced on solid medium was 18, but only five in liquid medium. On both media, the colchicine treatment for 8 days gave the maximum level of tetraploid induction. Therefore, it was found that the treatment of shoot tip explants on agar medium containing 2.0 mg l⁻¹ BA, 0.05 mg l⁻¹ NAA, and 0.2% (w/v) colchicine for 8 days was the most efficient way of inducing tetraploid ginger. Induced tetraploid strains, ‘4× Kintoki’, ‘4× Sanshu’, and ‘4× Philippine cebu 1’, had higher pollen fertility and germinability than the diploid counterparts, i.e., in the diploid strains, pollen fertility ranged from 0.3 to 6.2% and the germination rate from 0.0 to 0.1%, while in the tetraploid strains, pollen fertility ranged from 27.4 to 74.2% and the germination rate from 4.8 to 12.9%.     

Effect of phytohormones on in vitro shoot multiplication and rooting of lime Citrus aurantifolia (Christm.) Swing

Multiple shoots were produced from node explants of lime (Citrus aurantifolia (Christm.) Swing) on MS medium supplemented with 6-benzylaminopurine (BAP), 6-furfurylaminopurine (kinetin) and α-naphthaleneacetic acid (NAA). The highest number of shoots, nine shoots per node, were produced on a medium containing 2 mg l⁻¹ BAP (8.8 μM), 1 mg l⁻¹ kinetin (4.6 μM) and 1 mg l⁻¹ NAA (5.4 μM). Depending on the concentration of BAP and kinetin, NAA either inhibited, stimulated or did not affect shoot multiplication, which also depended on the cytokinin level. Maximum shoot length was obtained from treatments containing 0.5 mg l⁻¹ BAP (2.2 μM) combined with 1 mg l⁻¹ kinetin (4.6 μM) and 0.5 mg l⁻¹ NAA (2.7 μM). The largest leaves of resultant shoots were produced on a medium containing 0.5 mg l⁻¹ each of kinetin (2.3 μM) and NAA (2.7 μM). Transferring in vitro shoots to rooting media containing indole-3-butyric acid (IBA) and NAA produced complete plantlets. The highest rooting percentage was obtained on a medium containing either 1 mg l⁻¹ NAA (5.4 μM) alone or 0.5 mg l⁻¹ NAA (2.7 μM) combined with 2 mg l⁻¹ IBA (9.6 μM), whereas the highest number of roots were produced on a treatment containing both 2 mg l⁻¹ NAA (10.8 μM) and 2 mg l⁻¹ IBA (9.6 μM). Roots elongated most on treatments containing 0.5 mg l⁻¹ of either NAA (2.7 μM) or IBA (2.4 μM). Shoot growth associated with the rooting phase was the highest in response to 2 mg l⁻¹ IBA (9.6 μM) or 0.5 mg l⁻¹ NAA (2.7 μM). Plantlets that survived acclimatization, 82%, exhibited normal growth in soil under greenhouse conditions.     

Seasonal variations in leaf gas exchange of plantain cv. Hartón (Musa AAB) under different soil water conditions in a humid tropical region

The seasonal effect of soil water availability on leaf gas exchange of plantain plants cv. Hartón growing on two different texture soils (loamy and clayey) were evaluated. Soil water deficits corresponded to 48, 24 and 4 days without precipitation. Daily measurements of leaf gas exchange and microclimatic conditions were carried out at 2 h intervals in a humid tropical environment south of Maracaibo Lake, Venezuela. The results show that cv. Hartón is sensitive to conditions of low water deficit on loamy and to a much greater degree on clayey soils. A marked reduction in leaf conductance (g_s) was observed under severe as well as moderate deficit (below 50 mmol m⁻² s⁻¹) on clayey soils. Under low deficit g_s increases to values between 60 and 100 mmol m⁻² s⁻¹. The same trend was observed in plants on loamy soils but higher g_s for all conditions were obtained compared with plants on clayey soil. Stomatal closure produced a reduction of 85 and 55% of total assimilation (A_tot) for severe and moderate deficit in plants on clayey soils, respectively. While plants on loamy soil exhibited a 65 and 35% reduction, respectively. Water use efficiency (WUE) consistently decreased as available soil water decreased on both soil types. Independently of soil water conditions, higher WUE were always obtained for loamy soils. This suggests that cv. Hartón does not have the ability to adjust the CO₂ assimilation to transpiration ratio in order to optimize gas exchange. This evidences the importance of maintaining high conditions of available soil water in order to avoid lower assimilation rates that probably influence negatively on yield and fruit quality.     

Optimising the organic components of topsoil mixtures for urban grassland

In order to optimise the organic components of topsoil mixtures for urban grassland, we conducted two pot experiments, each with seven topsoil mixtures and perennial ryegrass (Lolium perenne) as the experimental crop. The mineral base material of the topsoil mixtures was a blend of crushed bedrock (0–2 mm), sand and agricultural topsoil. The organic components comprised three types of organic waste-based products (WBP), namely sewage sludge (SS), water sludge (WS) and garden-park compost (GPC), which were added in varying ratios to a total amount of 0.3 m³ WBP m^?3. In both experiments, mineral nitrogen (N) availability was the key limiting factor for plant growth. Plant growth increased with increasing amounts of the N-rich SS, whereas WS and/or GPC alone resulted in sparse biomass production. Topsoil mixtures with 0.1 m³ m^?3 each of SS, WS, GPC or with 0.1 m³ SS m^?3 and 0.2 m³ WS m^?3 resulted in favourable growth patterns and acceptable soil chemical properties. Topsoil mixtures containing ≤0.1 m³ SS m^?3 can therefore be recommended for the establishment of urban grassland. With >0.1 m³ SS m^?3, N and phosphorus (P) were applied in excess, causing intensive plant growth and strongly increased readily available phosphorus (P-AL) content in topsoil. We therefore suggest revision of the current Norwegian regulations, which permit inclusion of 0.3 m³ SS m^?3 in topsoil mixtures for urban greening.